Intrinsically Stretchable OLEDs with a Designed Morphology-Sustainable Layer and Stretchable Metal Cathode

Intrinsically Stretchable OLEDs with a Designed Morphology-Sustainable Layer and Stretchable Metal Cathode | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Article Intrinsically Stretchable OLEDs with a Designed Morphology-Sustainable Layer and Stretchable Metal Cathode Jin-Woo Park, Je-Heon Oh, Kun-Hoo Jeon This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-4215709/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 26 Jul, 2024 Read the published version in npj Flexible Electronics → Version 1 posted 11 You are reading this latest preprint version Abstract Recently, the growing desire to conformally integrate electronics with the human body in the form of wearable devices has spurred the need for additional form factors, skin-like softness, and stretchability of organic light-emitting diodes (OLEDs). Traditional intrinsically stretchable OLED ( is- OLED) approaches have focused on improving the luminance and stretchability through methods such as blending materials to endow the component layers with stretchability and complex lamination processes. However, the designed microstructure of the blended layer cannot be maintained due to the different orthogonality between the solvents of subsequently coated layers. In addition, the lamination method often leads to degradation of the performance due to delamination induced by formed defects. To overcome these challenges, we developed a sequentially coated is- OLED and confirmed the maintenance of the designed morphologies of each layer and a highly stretchable metallic is- cathode. Our is- OLEDs achieved a maximum total luminance of 3,151 cd m -2 and a total current efficiency of 5.4 cd A -1 (on both the anode and cathode sides). Furthermore, our is- OLEDs exhibited a higher static stretchability of up to 70% than previous work and a notable cyclic stretchability, maintaining 80% of the luminance at 0% strain after 300 stretching cycles under 40% strain. This breakthrough in the fabrication process, coupled with the use of novel stretchable materials, represents a significant step forward in the field of is- OLED technology, potentially leading to a new era of highly durable and efficient soft electronic devices. Physical sciences/Materials science Physical sciences/Optics and photonics Figures Figure 1 Figure 2 Figure 3 Figure 4 INTRODUCTION Organic light-emitting diodes (OLEDs) are pivotal in current display technology because they offer advantages such as high energy efficiency and vibrant color reproduction. 1–3 The recent shift from rigid devices toward soft electronics has sparked interest in intrinsically stretchable OLEDs ( is- OLEDs) that mimic skin-like properties. 4–16 While significant progress has been made in enhancing the luminance and stretchability of is- OLEDs, challenges persist in the manufacturing processes and intrinsically stretchable material design. Previous is- OLED studies have focused on improving the stretchability of inherently rigid organic layers by blending various materials, such as Triton X-100 (TX) and poly(ethylene glycol)-block-poly(propylene glycol)-block-poly(ethylene glycol) (PEO-PPG-PEO) additives and polyurethane (PU) and polystyrene-block-polybutadiene-block-polystyrene (SBS) elastomers, which change the microstructure from rigid to stretchable. 12–18 To fabricate is- OLEDs with organic layers, solution coating, such as spin-coating, is usually performed. However, in many cases, the lack of solvent orthogonality between layers destroys the designed microstructure of the underlying layer, which significantly reduces the stretchability. 19,20 Hence, in previous works by others, lamination was used to build up the layers in is- OLEDs. In Zhang et al., emissive layer (EML) and electron transport layer (ETL) surfaces were joined, and in Liu et al., the ETL and cathode surfaces were laminated. In many cases, a lack of solvent orthogonality occurred between the EML, ETL, and cathode layer. The lamination process includes alignment, interfacing, and hot pressing. 12–15 During this process, misalignment and pressure-induced defects and voids induce insufficient layer contact, leading to delamination, dark spots, reduced fabrication yield, and decreased performance, especially under repeated stretching. 11 In conventional OLEDs, a metallic cathode is used due to the high density of free electrons and high charge carrier mobility. However, due to the inherent rigidity of metals, these cathodes were not considered as stretchable electrodes for use in is- OLEDs. In previous works on is- OLEDs, silver nanowires (AgNWs), graphene, and poly(2,3-dihydrothieno-1,4-dioxin)-poly(styrenesulfonate) (PEDOT:PSS) were used as stretchable cathodes, which are very limited candidates. AgNWs were embedded in an elastomer matrix to impart stretchability. Hence, they had to be fabricated on a separate substrate, followed by a physical lamination process onto the precoated organic layers. 13,15 Graphene cannot be directly synthesized on ETL surfaces; hence, its integration also involves a complex transfer process onto cathode surfaces, necessitating a subsequent lamination process. 13 While the PEDOT:PSS cathode can be directly spin-coated on organic surfaces, this approach risks damaging the underlayer due to the effect of the polar solvent on the ETL and the post-patterning process. As a result, PEDOT:PSS cathodes were also fabricated by a lamination process after the separate fabrication of is- cathodes. 12 In summary, in addition to their inferior conductivity compared to that of conventional metallic cathodes, these materials inevitably require a manual lamination process during the fabrication of is- OLEDs. In this study, we developed a hybrid fabrication process employing sequential solution coating and thermal evaporation, eliminating the need for a lamination process. We developed a newly designed morphology-sustainable is- ETL and a highly stretchable metallic is- cathode. The is- ETL not only ensures a uniform surface but also sustains the designed morphology of the is- EML, thereby enhancing the electrical and mechanical properties of is- OLEDs. Furthermore, by adjusting the deposition conditions and controlling the thickness of the conventional brittle Ag metal film, we successfully fabricated a stretchable Ag electrode with high electrical conductivity. As a result, our device achieved a maximum total luminance of 3,151 cd m -2 and a current efficiency of 5.4 cd A -1 , maintaining approximately 50% performance at 70% strain and 80% performance after 300 cycles of stretching tests. This work explores new stretchable materials and fabrication processes and discusses potential challenges and advancements in mechanical and electrical properties, paving the way for the promising future of is- OLED technology. Figure 1 Design of is- OLEDs and characterization of the is- ETL and is- cathode. a Schematic of an is- OLED structure from the is- anode to the upper ETL. b is- OLED fabrication process with sequential coating. c Device structure and components of an is- OLED. d Schematics of the is- EML morphology change after ETL solvent coating. Based on the various analysis results, by adding Triton X into the ETL solvent, the SY chains maintain an extended morphology after the is- ETL coating process, resulting in high stretchability. e Schematics of the is- cathode morphology and electron conducting mechanism under stretching conditions. RESULTS AND DISCUSSION Designs of intrinsically stretchable OLED Figure 1a shows a schematic image of the is- OLEDs fabricated in this work. Figure 1b summarizes our sequential coating processes from the is- anode to the upper ETL. As shown in Fig. 1c, for the is- OLEDs, an intrinsically stretchable hole transport layer ( is- HTL) is formulated from PEDOT:PSS and the nonionic surfactant TX, and an intrinsically stretchable EML ( is- EML) is composed of a commercial EML, Super Yellow (SY) and TX. 16 TX affects the conformation and microstructure of PEDOT:PSS and SY, resulting in highly stretchable is- HTL and is- EML. 16 As illustrated in Fig. 1c, an intrinsically stretchable ETL ( is- ETL) is spin-coated on the is- EML. Prior research has employed materials such as polyethylenimine (PEI) and polyethyleneimine ethoxylated (PEIE) for is- OLED ETLs due to their inherent stretchability and work function alignment properties, often in combination with electron-injecting materials such as ZnO, Cs 2 CO 3 , and poly(9,9-bis(3’-(N,N-dimethyl)-N-ethylammoinium-propyl-2,7-fluorene)-alt-2,7-(9,9-dioctylfluorene))dibromide (PFN-Br). 12–16 Among them, PFN-Br stands out due to its superior electron injection and hole blocking capabilities, as well as its ability to facilitate a uniform surface. Nonetheless, the binary ETL composed of PFN-Br and PEIE has been found to offer limited stretchability and to adversely affect the underlying is- EML during the solution coating process, highlighting the necessity for advanced material design. Most solvents dissolve most nonionic surfactants, potentially altering the morphology of the organic layers including a nonionic surfactant during sequential coating. Furthermore, the mechanical and electrical properties of is- EMLs are strongly affected by the morphology of the conjugated polymers. 12,16 Our study mitigated this by incorporating TX across all coating layers from the is- HTL to is- ETL, ensuring the presence of TX on the underlayer surface to sustain the designed morphology of conjugated polymers, as shown in Fig. 1d. The incorporation of TX into the PFN-Br and PEIE matrix has been shown to enhance both the mechanical and electrical properties of the is- OLED, leading to improved overall device performance. Following the is- ETL coating process, an is- metal cathode is developed using evaporation, as shown in Fig. 1e. Previous is- OLED research employed stretchable electrode materials such as AgNWs, PEDOT:PSS, and graphene as cathodes. 12–16 However, these stretchable electrodes often exhibit significant roughness, inferior electrical characteristics, or chemical instability. Furthermore, they require either a solution process or a complicated transfer process, which damages the underlying organic layers and complicates patterning. 11,21,22 Hence, the development of new stretchable electrode materials is imperative. For high-performance is- OLEDs, electrode materials such as stretchable Al or Ag films are expected to be most effective because of their inherently high charge carrier density and mobility. 3 Such materials can be deposited by thermal evaporation, minimizing damage to the underlying organic layers, and are easily patterned. However, metal films inherently lack stretchability. 23–25 To address this, modifying the interaction with the underlayer and adjusting the deposition conditions are crucial. We successfully fabricated a stretchable Ag electrode with high electrical conductivity by fine-tuning the deposition conditions and optimizing the thickness of the traditionally brittle silver metal film. The precisely adjusted evaporation conditions for the stretchable metal cathode resulted in only microcracks on the surface under stretching conditions, enabling efficient electron movement between the microcracks (Fig. 1e). Figure 2 Design and characterization of is- ETLs for highly stretchable is- functional layers. a UV‒vis absorption spectra of is- EMLs with various TX blending ratios, and solvent coating effect on the is- EMLs. b UV-vis absorption spectra of is-EMLs before and after TX-blended solvent coating (TX1 = 1 mg ml − 1 , TX2 = 2 mg ml − 2 , TX4 = 4 mg ml − 1 ). c Photoluminescence spectra of is- EMLs before and after TX-blended solvent coating. d COS of is- EMLs before and after TX-blended solvent coating. e COS of is- ETLs with various component ratios when coated on PDMS or is- EMLs. f UPS intensity of is- ETL and Ag films with various TX ratios. g Current density of electron-only devices with various ETL component ratios. h Energy-level alignment diagram for the conventional OLED device with an is- ETL. i V - L curve, j J - V curve, and k ε c - L curve of the conventional OLED device with an is- ETL on a glass substrate. Designed morphology sustainable electron transport layer PFN-Br, distinguished by its high lowest unoccupied molecular orbital (LUMO) level of 2.7 eV and low highest occupied molecular orbital (HOMO) level of 5.6 eV, was selected as the is- ETL (Fig. 1c). It offers significant advantages for electron injection and hole blocking in OLED structures. 12,26 Furthermore, the addition of PEIE contributes to a notable increase in the stretchability of the material, reaching approximately 70% strain (Supplementary Fig. 1). However, the stretchability of PFN-Br:PEIE is lower than the 80% crack onset strain (COS) of the is- EML. Additionally, when PEIE or PFN-Br:PEIE solution is coated on the is- EML, a significant reduction in the COS to 40% occurs (Supplementary Fig. 2). This reduction suggests that the impact on stretchability is due not only to the intrinsic properties of the ETL but also to changes in the underlying is- EML layer. For the is- EML, TX mixed with SY-conjugated polymers (Fig. 1c) alters the morphology of the polymers from coiled to extended, resulting in high stretchability and electrical properties. 16 This morphological change is evident through the redshifted absorbance (Abs), blueshifted photoluminescence (PL), and changes in the atomic force microscopy (AFM) surface phase (Fig. 2a, Supplementary Figs. 3 and 4). Here, we coated various solvents on is- EMLs to investigate the effect of dissolution of is- EMLs in the solvent on the changes in the conformation and morphology of the is- EMLs (Fig. 2a). Regardless of the TX concentration in the SY and ETL materials, applying a solvent coating on the is- EML to coat the is- ETL reverts the Abs, PL, and phase changes to those of pristine SY (Supplementary Figs. 2, 3, and 4). Since TX, a nonionic surfactant, is soluble in most organic solvents, we can anticipate that the characteristics of the EML may change when the TX present on the SY surface is washed away. Therefore, to maintain the morphology of the is- EML, TX was also incorporated into the ETL. This addition ensures that the designed morphology from the HTL to the ETL is maintained during the continuous coating process. Figures 2b and 2c confirm that mixing TX with the solvent sustains the redshifted Abs and blueshifted PL peaks after coating, akin to the behavior of the is- EML. Moreover, increasing the TX concentration better sustain the is- EML Abs and PL peaks up to 4 mg ml − 1 . Figure 2d shows the effect of TX on the COS of the is- EML (Supplementary Fig. 2, Supplementary Fig. 9). Mixing SY with TX increases the COS. Applying the solvent coating alone decreases the COS to 40%, whereas the solvent containing TX yields a COS of 60% at 1 mg ml − 1 , 80% at 2 mg ml − 1 , and 90% at 4 mg ml − 1 . These findings suggest that the TX-blended solvent maintains the is- EML morphology, ensuring high stretchability. Therefore, coating of an ETL solution with TX is crucial for preserving the extended morphology of the is- EML. Figure 2e shows the mechanical characteristics of the ternary blends of PFN-Br, PEIE, and TX. TX increases the COS of the is- ETL by increasing the free volume within the material and decreasing the crystallinity of the conjugated polymer (Supplementary Fig. 1). 16,26 Hence, the ternary blend of the is- ETL with a ratio of 2:2:2 inherently exhibits high stretchability and is capable of withstanding up to 100% COS. When this is- ETL is applied over the is- EML, the COS increases as the ratio of TX increases, matching the COS of the is- EML itself. The introduction of TX into the PFN-Br:PEIE ETL has dual effects: providing high stretchability of the is- ETL and sustaining the designed morphology of the is- EML. This stretchability alignment between the is- ETL and is- EML is a significant achievement, ensuring that the overall device can maintain its structural integrity and functional performance even under considerable mechanical strain. Furthermore, the ternary blended is- ETL shows a uniform surface morphology, as shown in Supplementary Fig. 10. Figure 2f shows the electrical properties of the is- ETLs. Ultraviolet photoelectron spectroscopy (UPS) measurements, based on the TX blending ratio, reveal that the work function of 4.8 eV for the pristine Ag film decreases to 3.3 eV following coating with a PFN-Br:PEIE (2:2) solution. Additional blending of the ETL with TX results in work functions of 3.25 eV for a 2:2:1 ratio and 3.35 eV for a 2:2:2 ratio, indicating similar electron injection characteristics (Supplementary Fig. 12, Supplementary Table 1). Triton X is an electrical insulator, but we estimate that the dipole of the nonionic surfactant TX lowers the work functions of PEIE and PFN-Br. As shown in Fig. 2g, we fabricated electron-only devices using the is- ETLs, the detailed structure of which is presented in Supplementary Fig. 13. Compared to PFN-Br, the PFN-Br:PEIE ETL exhibits a higher current density. Furthermore, as the TX blending ratio increases, the electron current density correspondingly increases. This finding implies that the TX-blended is- ETL improves the electron transport properties by maintaining the extended morphology of the is- EML. Then, we fabricated devices with a conventional OLED structure using the is- ETLs (Fig. 2h). Figure 2i demonstrates the improved performance obtained with the TX-blended is- ETLs compared to that obtained with the 2:2 ratio, and the increase in the efficiency is shown in Fig. 2k. Hence, the TX-blended is- ETLs not only exhibit inherently high mechanical and electrical properties but also help sustain the designed morphology of the is- EML, thereby enhancing its mechanical and electrical characteristics. Although the 2:2:1 ratio results in a slightly better performance, we chose a 2:2:2 ratio of the is- ETL for the is- OLED fabrication to enhance the is- EML stretchability. Fig. 3 Fabrication and characterization of is- OLEDs. a Schematics of the is- cathode surface morphologies from a thin Ag to thick Ag film. b Sheet resistance, stretchability of the is- cathode, and luminance of the is- OLED at various is- cathode thicknesses. c Optimal Ag evaporation conditions for the is- cathode. d Resistance change in Ag cathode films with various thicknesses ranging from 30 nm to 70 nm during static stretching tests. e Resistance change in the 60 nm is- cathode during cyclic stretching tests at 20% and 40% strain. f TEM cross-sectional image of the is- OLED. g SEM image of the is- cathode surface at 0% and 40% strain. h SEM image of the is- cathode surface when stretched to 60% strain and released to 0% strain from 40% strain. Intrinsically stretchable Ag metal cathode To render the Ag film stretchable, we optimized the deposition parameters (evaporation rate and thickness) and the substrate. The structure and properties of the film largely depend on the substrate. Since our cathodes are positioned on top of the devices rather than directly above the elastomer substrate, options for the deposition surface are more constrained than those in previously reported stretchable metal studies. 27–30 The deposition surface must have ( 1 ) a smooth surface, ( 2 ) high compatibility (adhesion) with Ag atoms, and ( 3 ) appropriate energy levels for electron injection. PFN-Br:PEIE:TX meets all these requirements because of its low surface roughness and adequate energy level (Supplementary Fig. 10 and Fig. 2f ). Additionally, the amine groups in PEIE are compatible with Ag atoms through coordination bonds, functioning as seed layers for ultrathin Ag films. 23 The evaporation rate and thickness were optimized to achieve both good optoelectrical properties and stretchability. Ag films deposited on the elastomer substrate form three-dimensional islands according to the Volmer–Weber growth mechanism and eventually connect to form a continuous film with increasing thickness (Fig. 3 a). 31 A greater thickness ensures high bulk conductivity but can also make the film brittle. A high evaporation rate leads to continuous films by suppressing Volmer–Weber growth, while a lower rate enhances stretchability due to the interlocking interface between the metal and substrate and the optimal grain size. 29,32 Therefore, we aimed to scale down the deposition thickness and rate until superior optoelectrical properties could be maintained (Figs. 3 b, c, and d). We selected Ag films with a thickness of 60 nm deposited at a rate of 1 Å s − 1 as our stretchable cathode. To determine the optimal deposition parameters, we fabricated our stretchable cathode on the is -OLEDs (Fig. 1a), We then characterized its optoelectrical properties, focusing on maximum luminance (Fig. 3 b, c) and cathode conductivity under static and cyclic stretching conditions (Fig. 3 d, e). The conductivity rapidly decreases below 40 nm in thickness due to the poor connectivity between Ag grains (Figs. 3 b, d and Supplementary Fig. 14). Ag films thicker than 60 nm have high conductivity and show a superior luminance of over 3,200 cd m − 2 when used as a cathode in is- OLEDs but cannot endure strains above 60% due to the brittle nature of the dense, continuous Ag grains (Figs. 3 b, d, Supplementary Fig. 14, and Supplementary Fig. 16). A 60 nm stretchable cathode exhibits a low sheet resistance of 6 Ω sq − 1 and a maximum luminance of more than 2,300 cd m − 2 and maintains a resistance change of R R 0 − 1 < 10 under 70% strain, simultaneously ensuring high electrical conductivity and mechanical stretchability (Figs. 3 b, c, d, and Supplementary Fig. 16). Additionally, the material maintains its conductivity during 200 cycles of 40% strain stretching (Fig. 3 e). We investigated the relationship between the microstructures and electrical properties of Ag films via scanning electron microscopy (SEM), transmission electron microscopy (TEM), and time-of-flight secondary ion mass spectrometry (TOF-SIMS). Partially connected morphologies of Ag grains are observed, as shown in Figs. 3 f and g. The actual grain size of the deposited film is approximately 35 nm (note that we describe the deposition thickness values measured by a quartz crystal sensor during thermal evaporation). Due to the slow deposition process, an intermixed region of Ag and organic layers is observed in the TOF-SIMS and TEM cross-section images (Fig. 3 f and Supplementary Figs. 17–19). No observable channel cracks appear on the film in the optical microscopy (OM) images until 60% strain (Supplementary Fig. 20). Instead, microcracks develop throughout the film during the stretching process. Under stretching, strain is released by widening of preexisting cracks while conducting paths are preserved through connected grains (Figs. 3 d, g, and h). The cracks reversibly close after strain release; thus, the Ag cathode also shows high electrical and mechanical stability under cyclic stretching (Figs. 3 e, h and Supplementary Fig. 23). Our stretchability of the Ag cathode seems to be based on two unique structural features of is- OLEDs. First, the multilayers under the cathode (from the is- HTL to is- ETL) provide a gradient in the Young’s modulus between the soft elastomer substrate and the stiff metal cathodes. This enhances the stretchability of the cathode compared to structures without multilayer configurations (Supplementary Fig. 24). Second, the partially interconnected Ag morphologies allow additional layers to be overcoated on the cathodes. We overcoated cesium carbonate-doped PEIE (d-PEIE) on a Ag cathode, which possesses superior electron injection properties. 33 If d-PEIE is placed between our is- ETL and is- cathode, it could hinder electron transport due to its electrically insulating nature and disrupt the intended Ag nucleation and growth processes by altering the surface properties. However, by applying it as an overcoating layer above the cathode, it primarily influences the lowering of the energy barrier for electron injection through channels within Ag films. Therefore, the d-PEIE overcoating layer was considered to contribute to the high luminance and improved stretchability of the is- OLEDs (Supplementary Fig. 25). Figure 4 Device performance of is- OLEDs and deformable displays. a Schematics of the is- OLED structure and thickness. b Energy-level alignment diagram of the is- OLED. c J - V - L curve of the is- OLEDs. d Relative L change ( L ∙ L 0 − 1 ) of the is- OLEDs during static stretching tests when operated at 8 V. e L ∙ L 0 − 1 changes of the is- OLEDs during 40% strain cyclic stretching tests. f Radar plot comparing the electroluminescence (EL) performance, stretchability, and fabrication complexity of is- OLEDs produced using the sequential coating or lamination method. The fabrication complexity corresponds to the number of transfer and lamination processes during the is- OLED fabrication process. g Optical images of the is- OLEDs with an original emission area of 3.0 × 3.0 mm 2 operated under various strains. h Optical photographs of 3X2 is- OLED array devices operated under various strains and deformations. Fully intrinsically stretchable OLED After detailed characterization of the is- ETL and is- cathode, is- OLEDs were fabricated. The fabrication involved sequential coating of the is- ETL, is- cathode, and an upper ETL over the is- EML and is- HTL based on AgNW-embedded polydimethylsiloxane (PDMS). The structural design and energy-level alignment of these devices are illustrated in Figs. 4a and 4b. Figure 4c shows the characteristic current density–voltage–luminance ( J - V - L ) curves for the is- OLEDs. These devices display a turn-on voltage of 6 V, achieving a maximum brightness of approximately 2,340 cd m − 2 at 9 V, for a measurement taken from the AgNW side. The maximum current efficiency recorded for this side is approximately 4.2 cd A − 1 . On the opposite side, where a semitransparent Ag cathode film is used, the performance is approximately 40% of that observed on the AgNW side. This side shows a luminance of 811 cd m − 2 and a current efficiency of 1.2 cd A − 1 . The diminished performance on this Ag side is primarily due to its lower transmittance and reflectance compared to those on the AgNW side. When considering the total performance of the device, combining both the anode and cathode sides, the overall luminance reaches an impressive 3,151 cd m − 2 , with a corresponding current efficiency of 5.4 cd A − 1 . This indicates the high overall performance of the is- OLEDs, demonstrating the effectiveness of the sequential coating process and the synergy between the is- ETL and is- cathode in enhancing the device efficiency and brightness. The stretchability of the is- OLEDs was tested to evaluate their durability and adaptability under mechanical stress. These tests involved both static and cyclic stretching tests, with the outcomes presented in Fig. 4d, focusing on the relative luminance change in response to various levels of strain at 8 V. At 0% strain, the average luminance across five samples was recorded as 791 cd m − 2 . As the strain increases, the devices demonstrate remarkable resilience. Up to a 20% strain at 8 V, there is a negligible reduction in performance, indicating a high level of stretchability. However, as the strain is further increased, the luminance gradually decreases. At 40% strain, the devices maintain approximately 75% of their original luminance. This value decreases to approximately 55% at 60% strain and further decreases to approximately 45% at 70% strain. These results are comparable to those achieved by devices using stretchable electrodes such as AgNWs and PEDOT:PSS. 12–14,16 This performance underlines the significant potential of metal-based stretchable cathodes in future applications. Figure 4d illustrates the changes in the performance of the is- OLEDs under cyclic stretching conditions at 40% strain. A special jig for the cyclic test is shown in Supplementary Fig. 26. In the early stages of the cyclic stretching test, specifically up to 50 cycles, the performance of the devices decreases, and the luminance decreases to approximately 85% of its original value. However, when the test is extended to 300 cycles, the luminance of the devices remarkably stabilizes, maintaining approximately 80% of the initial value. This indicates a significantly greater cyclic stretchability than that reported in previous studies using lamination processes, which exhibited a performance below 80% after 100 cycles at 15% and 40% strain. 12,14 Notably, our devices maintain stable performance for up to 300 cycles, surpassing the 200 cycles achieved in similar studies using sequential coating. 16 After the cyclic test, the top surface of the is- OLEDs was observed via SEM (Supplementary Fig. 27). This analysis reveals the formation of microcracks on the surfaces of the is- OLEDs due to stretching. However, microcracks and crack closure are vital characteristics, as they allow for continued flow and injection of charge across the affected areas, ensuring sustained device functionality. This resilience of the is- OLEDs under cyclic stretching, particularly their ability to maintain a high level of performance after 300 cycles at 40% strain, is an significant improvement over previous devices. 12–14,16 These results demonstrate the superior mechanical and electrical properties of the is- ETL and is- metal cathode compared to those achieved with conventional stretchable electrodes. 12–14,16 Figure 4f presents a radar plot comparing the performance and fabrication complexity of is- OLEDs made using traditional lamination processes and our sequentially coated is- OLEDs (Supplementary Table 2). While the luminance and efficiency are similar or slightly lower than those achieved with lamination methods, our is- OLEDs exhibit higher static stretchability and notably superior cyclic stretchability. In terms of fabrication complexity, our approach shows the most advantageous characteristics, indicative of the reduced need for lamination and transfer processes during the fabrication process. The sequentially coated is- OLEDs, made using the designed morphology-sustainable is- ETL and is- metal cathode, simplify the traditionally complex processes associated with lamination methods, achieving high levels of cyclic stretchability. Figure 4g depicts the light emitted from an is- OLED when it is stretched. The image shows that the device emits light consistently across its entire surface area both in a neutral state (0% strain) and under significant stretching (up to 70% strain). Further expanding on the capabilities of these devices, Fig. 4h shows a 3×2 array device fabricated using the is- OLEDs subjected to stretching. The detailed structure of this array is illustrated in Supplementary Fig. 28. This array device shows stable light emission up to 50% strain. Furthermore, the array device also demonstrates resilience to various other forms of deformation, including bending, folding, and crumpling. This ability to maintain stable light emission even under deformation conditions is a testament to the mechanical robustness and versatility of these devices. In summary, this study has made significant strides in the field of is- OLEDs by innovating and developing new stretchable component materials, such as designed morphology-sustainable is- ETLs and is- Ag metal cathodes. These advancements have been crucial in enhancing the overall performance of is- OLEDs. The meticulously adjusted formulation of PFN-Br, PEIE, and TX blended into the is- ETL has been instrumental in enhancing both the mechanical and electrical properties of is- OLEDs. The blending of PFN-Br and PEIE has demonstrated the ability to form a stretchable matrix simultaneously exhibiting high electron injection characteristics. Additionally, the incorporation of TX into this blend has been effective in sustaining the morphology of the underlying is- EML, leading to simultaneous improvements in both the mechanical and electrical properties of the is- EML and is- ETL. The is- cathode, engineered under controlled deposition conditions, has achieved significant advancements in terms of morphology control and adhesion with the is- ETL. This has led to the creation of a metal cathode that not only is highly stretchable but also maintains excellent electrical conductivity, which is a critical attribute for effective is- OLED operation. Furthermore, this research represents a departure from more complex lamination techniques through rational material engineering and optimized device construction. This approach significantly contributes to simplifying the fabrication process, making it more accessible for the development of next-generation stretchable optoelectronic devices. While acknowledging that the current performance of these is- OLEDs still lags behind that of conventional OLEDs, this study underscores the immense potential for future enhancements. In particular, the prospects of improving the performance through fine-tuning aspects such as the Ag stretchable cathode as well as the thickness and combination of the ETL are promising. Looking ahead, the continued development and utilization of stretchable metallic cathodes are expected to lead to significant performance improvements in is- OLEDs, opening up new possibilities and applications in the realm of flexible and wearable electronics. METHODS Preparation of is- EML and is- HTL For preparation of the is- EML solution, TX (Sigma‒Aldrich) was first dissolved in toluene at a concentration of 2.5 mg ml -1 . Then, SY (PDY-132, Sigma‒Aldrich) was blended in the TX-dissolved toluene at a concentration of 5 mg ml -1 . The blended solution was stirred at 300 rpm for 12 h at 60 ℃. After stirring, the is- EML was spin-coated on the is- HTL composed of a 1:1 solution of PEDOT:PSS (Al 4083, Heraeus Clevios) and isopropyl alcohol (IPA) with 5 wt% TX. Preparation of is- ETLs and Upper ETL For the is- ETL and upper ETL, a PFN-Br:PEIE:TX solution and a d-PEIE solution were prepared. For the d-PEIE solution, PEIE (Sigma‒Aldrich, 37 wt%) and Cs 2 CO 3 (Sigma‒Aldrich) were codissolved in 2-methoxyethanol (for which the weight ratio of PEIE to Cs 2 CO 3 was 10:1) at a 4 wt% concentration. After sonication of the d-PEIE solution via ultrasonication, the d-PEIE solution was stirred at 80°C for 12 hours. For the PFN-Br:PEIE:TX solution, PEIE and TX were dissolved in methanol at a concentration of 4 mg ml -1 . Then, 2 mg of PFN-Br (Ossila) was dissolved in 0.5 ml of PEIE and 0.25 ml of a TX-blended solution (weight ratio of PFN-Br:PEIE:TX of 2:2:1) or 0.5 ml of a TX-blended solution (weight ratio of PFN-Br:PEIE:TX of 2:2:2). Mechanical characterization of is- EMLs , is- ETLs, and is- cathode For the stretchable substrate, a PDMS substrate was cured on a polyethylene terephthalate (PET) substrate. The PDMS (Sylgard 184, Dow Corning) was prepared by mixing the base and agent at a 10:1 weight ratio and spin-coating the mixture on the PET substrate at 500 rpm for 30 s. The spin-coated PDMS was cured at 120 ℃ for 12 h. Then, the cured PDMS was peeled off from the PET substrate and used as a stretchable substrate. For mechanical characterization of the is- EMLs, COS analysis was performed for various solvent treatments. On the cured PDMS substrate, oxygen plasma was applied at 140 W for 90 s, and the is- HTL was spin-coated at 500 rpm for 60 s and 1000 rpm for 10 s. PDMS with the is- HTL was annealed on a hot plate at 120 ℃ for 15 min. Then, the sample was transferred to a glove box filled with nitrogen gas. The is- EML was spin-coated on the is- HTL at 1500 rpm for 30 s and annealed at 90 ℃ for 10 min. Then, MeOH, IPA, and 2-methoxyethanol were spin-coated on the is- EML at 4000 rpm for 30 s and annealed at 100 ℃ for 10 min. In the case of the is- ETL, the is- ETL was spin-coated at 5000 rpm for 30 s on the plasma-treated PDMS substrate and annealed on the hot plate at 90 ℃ for 10 min in the glove box. The is- EMLs and is- ETLs on the PDMS substrate were loaded on a homemade stretching jig. Strain was applied in increments of 10% from 0–100%. Fabrication of the ITO anode based rigid OLEDs The slide glass substrate (Paul Marienfeld GmbH & Co. KG, Germany) was cut to 2.5 cm × 2.5 cm and sequentially washed in the sonication baths of acetone, IPA, and deionized water for 5 min each. On precleaned glass, ITO (150 nm thick) was deposited using direct current (DC) magnetron sputtering and annealed at 300 ℃ for 30 min inside a glove box filled with nitrogen gas. On the ITO-coated glass, oxygen plasma was applied at 140 W for 90 s. On the plasma-treated ITO glass, an is- HTL solution was spin-coated at 2000 rpm for 60 s after being filtered through a 1 µm polytetrafluoroethylene (PTFE) syringe filter and annealed at 120 ℃ for 20 min. The sample was then transferred into a glove box filled with nitrogen gas. On the is- HTL, the is- EML was spin-coated at 1500 rpm for 30 s and annealed at 100 ℃ for 10 min. Then, the PFN-Br, PEIE, and TX-blended solution was spin-coated on the is- EML at 5000 rpm for 30 s and annealed at 100 ℃ for 10 min. Finally, the Al cathode was thermally evaporated on the is- ETL with a 150 nm thickness. Fabrication of electron only device For electron only device fabrication, 150 nm Ag anode was deposited on the pre-cleaned glass substrate using thermal evaporator. On the Ag anode, 0.5 wt% d-PEIE solution was spin coated at 5000 rpm for 30 s and annealed at 100 ℃ for 10 min. It was then transferred into a glove box filled with nitrogen gas. On the d-PEIE, is- EML was spin-coated at 1500 rpm for 30 s and annealed at 100 ℃ for 10 min. Then, PFN-Br, PFNBr:PEIE, PFNBr:PEIE:TX blend solution was spin-coated on the is- EML at 5000 rpm for 30 s and annealed at 100 ℃ for 10 min. Finally, Al cathode was thermally evaporated on the is- ETL with 150 nm thickness. Preparation of FOTS on Glass substrate A precleaned glass substrate was first treated by O2 plasma at 140 W for 90 s. Then, the glass substrate was vapor annealed in a desiccator with trichloro(1H,1H,2H,2H-perfluorooctyl)silane (FOTS, Sigma‒Aldrich) solution for 30 min and annealed at 150 ℃ for 30 min. Fabrication of is- OLEDs For the is- anode, 0.5 ml of a AgNW (with a diameter of 30 nm and a length of 30 µm; Novarials) solution (1 mg ml -1 concentration) was spray-coated on the FOTS-treated glass substrate using a patterned metal mask. On the AgNWs, an aerogel solution with 4 wt% ethanol was spin-coated at 1000 rpm for 30 s and annealed at 100°C for 10 min. Then, a PDMS solution in tetrahydrofuran (THF) solvent (base and agent ratio of 10:1 at 20 mg ml -1 ) was spin-coated on the aerogel surface at 1000 rpm for 30 s. Additionally, PDMS (base and agent ratio of 10:1) was spin-coated at 300 rpm for 30 s and cured at 120°C for 12 hours. After the curing process, the AgNW-embedded PDMS was released from the glass substrate. The released AgNW-embedded PDMS substrate was reattached to a glass substrate with the AgNW electrode facing up. Before coating with the is- HTL, oxygen plasma was applied at 140 W for 90 s. Then, an is- HTL solution was spin-coated at 500 rpm for 60 s and 1000 rpm for 10 s after being filtered through a 1 µm PTFE syringe filter and annealed at 120 ℃ for 15 min. The is- HTL-coated sample was transferred to a N 2 -filled glove box. In the glove box, the is- EML was spin-coated at 1500 rpm for 30 s and annealed at 90°C for 5 min. On the is- EML, is- ETLs was sequentially coated. An is- ETL solution (PFN-Br:PEIE:TX) was spin-coated at 5000 rpm for 30 s and annealed at 90°C for 5 min. Then, a Ag cathode was evaporated on the is- ETL at 1 Å s -1 up to 60 nm thickness. After the evaporation process, 4 wt% d-PEIE solution was spin-coated on the Ag surface at 1000 rpm for 30 s and annealed at 90°C for 5 min. Finally, the is- OLED was released from the glass substrate. The 3x2 array device fabrication process was almost the same as the is- OLED fabrication process. Only the anode and cathode patterns and glass size were different from those for the is- OLEDs. Other characterization methods The surface morphology of each film was characterized using AFM (NX-10, Park Systems) and field-emission scanning electron microscopy (FE-SEM, IT-500HR, JEOL). The PL spectra of the devices were measured using a spectrofluorometer (FP- 8550, JASCO Co.). The microstructures were characterized by TEM (JEM-ARM200F “NEO ARM,” JEOL) and energy-dispersive X-ray spectrometry (EDS, JED-2300T (Dual), JEOL). The luminance–voltage–current density ( L – V – J ) characteristics and EL spectra were measured using a 2400 Keithley Sourcemeter and a CS-200 (CS-2000) Konica-Minolta Chromameter. The optical transmittance of the devices was measured using an ultraviolet–visible (UV–VIS) spectrophotometer (V-650, JASCO Co.). Declarations ACKNOWLEDGEMENTS This work was supported by a National Research Foundation of Korea (NRF) Grant funded by the Korea Government (MSIT) (RS-2023-00302611) and the Technology Innovation Program Development Program ("20022479", "Development of deuterium oxide localization and deuterium benzene synthesis technology to improve OLED lifetime by 25%") funded by the Ministry of Trade, Industry & Energy (MOTIE, Korea). AUTHOR CONTRIBUTIONS J.-H. O., K.-H. J., and J.-W. P. designed the project. J.-H. O. and K.-H. J. carried out the experiments and analysis. J.-H. O., K.-H. J., and J.-W. P. wrote the paper. COMPETING INTERESTS The authors declare no competing financial interests. References Koo, J. H. et al. Flexible and Stretchable Smart Display: Materials, Fabrication, Device Design, and System Integration. Adv. Funct. Mater. 28 , 1801834 (2018). Chen, H. W. et al. Liquid crystal display and organic light-emitting diode display: present status and future perspectives. Light. Sci. Appl. 7 , 17168 (2018). Wang, S. M. et al. Towards high-power-efficiency solution-processed OLEDs: Material and device perspectives. Mater. Sci. Eng. R. Rep. 140 , 100547 (2020). Someya, T., Bao, Z. N. & Malliaras, G. G. The rise of plastic bioelectronics. Nature 540 , 379-385 (2016). Sekitani, T. et al. Stretchable active-matrix organic light-emitting diode display using printable elastic conductors. Nature Materials 8 , 494-499 (2009). Singh, M., Haverinen, H. M., Dhagat, P. & Jabbour, G. E. Inkjet printing-process and its applications. Adv. Mater. 22 , 673-685 (2010). Yook, K. S. & Lee, J. Y. Small molecule host materials for solution processed phosphorescent organic light-emitting diodes. Adv. Mater. 26 , 4218-4233 (2014). Chiba, T., Pu, Y. J. & Kido, J. Solution-processable electron injection materials for organic light-emitting devices. J. Mater. Chem. C 3 , 11567-11576 (2015). Liang, J. J. et al. Elastomeric polymer light-emitting devices and displays. Nat. Photonics 7 , 817-824 (2013). Gao, H., Chen, S., Liang, J. & Pei, Q. Elastomeric Light Emitting Polymer Enhanced by Interpenetrating Networks. ACS Appl. Mater. Inter. 8 , 32504-32511 (2016). Yin, H. et al. Structures and Materials in Stretchable Electroluminescent Devices. Adv. Mater. , e2106184 (2021). Zhang, Z. et al. High-brightness all-polymer stretchable LED with charge-trapping dilution. Nature 603 , 624-630 (2022). Zhou, H. et al. Graphene-Based Intrinsically Stretchable 2D-Contact Electrodes for Highly Efficient Organic Light-Emitting Diodes. Adv. Mater. 34 , e2203040 (2022). Liu, Y. et al. A Self-Assembled 3D Penetrating Nanonetwork for High-Performance Intrinsically Stretchable Polymer Light-Emitting Diodes. Adv. Mater. 34 , e2201844 (2022). Liu, W. et al. High-efficiency stretchable light-emitting polymers from thermally activated delayed fluorescence. Nat. Mater. 22 , 737-745 (2023). Kim, J. H. & Park, J. W. Intrinsically stretchable organic light-emitting diodes. Sci. Adv. 7 , eabd9715 (2021). Oh, J. H. & Park, J. W. Intrinsically Stretchable Phosphorescent Light-Emitting Materials for Stretchable Displays. ACS Appl. Mater. Inter. 15 , 33784-33796 (2023). Jeon, K. H. & Park, J. W. Light-Emitting Polymer Blended with Elastomers for Stretchable Polymer Light-Emitting Diodes. Macromolecules 5 , 8311-8320 (2022). Zhou, H. et al. Intrinsically stretchable low-dimensional conductors for wearable organic light-emitting diodes. Device 1 , 100060 (2023). Han, S. J. et al. Achieving Low‐Voltage Operation of Intrinsically‐Stretchable Organic Light‐Emitting Diodes. Adv. Funct. Mater. 33 , 2211150 (2023). Wu, W. Stretchable electronics: functional materials, fabrication strategies and applications. Sci. Technol. Adv. Mater. 20 , 187-224 (2019). Lee, H. et al. Stretchable organic optoelectronic devices: Design of materials, structures, and applications. Mater. Sci. Eng. R. Rep. 146 , 100631 (2021). Kang, H. et al. Polymer-metal hybrid transparent electrodes for flexible electronics. Nat. Commun. 6 , 6503 (2015). Bi, Y. G. et al. Ultrathin Metal Films as the Transparent Electrode in ITO‐Free Organic Optoelectronic Devices. Adv. Opt. Mater. 7 , 1800778 (2019). Park, S. I. et al. Theoretical and Experimental Studies of Bending of Inorganic Electronic Materials on Plastic Substrates. Adv. Funct. Mater. 18 , 2673-2684 (2008). Ohisa, S. et al. Conjugated Polyelectrolyte Blend with Polyethyleneimine Ethoxylated for Thickness-Insensitive Electron Injection Layers in Organic Light-Emitting Devices. ACS Appl. Mater. Inter. 10 , 17318-17326 (2018). Jiang, Z. et al. A 1.3-micrometre-thick elastic conductor for seamless on-skin and implantable sensors. Nat. Electron. 5 , 784-793 (2022). Zhu, T. et al. Highly stable and strain-insensitive metal film conductors via manipulating strain distribution. Mater. Horiz. 10 , 5920-5930 (2023). Han, S. et al. Enhanced stretchability of metal/interlayer/metal hybrid electrode. Nanoscale 13 , 4543-4550 (2021). Kim, S. W. et al. Omnidirectionally Stretchable Metal Films with Preformed Radial Nanocracks for Soft Electronics. ACS Appl. Nano. Mater. 3 , 7192-7200 (2020). Won, D. et al. Transparent Electronics for Wearable Electronics Application. Chem. Rev. 123 , 9982-10078 (2023). Kim, M. H. et al. Mechanically robust stretchable semiconductor metallization for skin-inspired organic transistors. Sci. Adv. 8 , eade298 (2022). Kim, J. H. & Park, J. W. Designing an electron-transport layer for highly efficient, reliable, and solution-processed organic light-emitting diodes. J. Mater. Chem. C 5 , 3097-3106 (2017). Additional Declarations (Not answered) Supplementary Files SupplementaryInformation.docx Supplementary Information Cite Share Download PDF Status: Published Journal Publication published 26 Jul, 2024 Read the published version in npj Flexible Electronics → Version 1 posted Editorial decision: revise 14 May, 2024 Review # 3 received at journal 13 May, 2024 Review # 2 received at journal 29 Apr, 2024 Review # 1 received at journal 28 Apr, 2024 Reviewer # 3 agreed at journal 16 Apr, 2024 Reviewer # 2 agreed at journal 15 Apr, 2024 Reviewer # 1 agreed at journal 15 Apr, 2024 Reviewers invited by journal 15 Apr, 2024 Submission checks completed at journal 05 Apr, 2024 First submitted to journal 04 Apr, 2024 Editor assigned by journal 04 Apr, 2024 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-4215709","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Article","associatedPublications":[],"authors":[{"id":291633675,"identity":"bd3f3c5e-2af0-4937-b28b-67026b78ddcf","order_by":0,"name":"Jin-Woo Park","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA+ElEQVRIiWNgGAWjYBACxgYQeUBCjh/ClwARzMRosTGWbCBWCwQcSEvccADBxa+FeUbuwc8VZw4nbr6RfOzhjwoLBv72A8zGFfgcNiMvWfLMjcPG226kpRvznJFgkDiTwJx4Bp+W2TkGkg0fDstuu5FjJs3YBvTLDQbmgw34tRj/BGph3Dwjx0zy5z8JBnkitJhJNtxIU9wgkWMmwdsgwWAA1JKIV8v8d2mWDWdsjCXOPEuT5jkmwWN4JrHZEJ8Ww56zh282HANGZXvyMckfNXVycscPH5bEq6WBB8oSSABTPLDoxQnkGWBa+A/gVTgKRsEoGAUjGAAAJRRQGac4cT4AAAAASUVORK5CYII=","orcid":"https://orcid.org/0000-0003-0965-373X","institution":"Yonsei University","correspondingAuthor":true,"prefix":"","firstName":"Jin-Woo","middleName":"","lastName":"Park","suffix":""},{"id":291633676,"identity":"df90c15f-bf38-47c2-b937-52b63dba7f28","order_by":1,"name":"Je-Heon Oh","email":"","orcid":"","institution":"Yonsei University","correspondingAuthor":false,"prefix":"","firstName":"Je-Heon","middleName":"","lastName":"Oh","suffix":""},{"id":291633677,"identity":"5a936306-2a44-417c-88ef-addca1e8abe8","order_by":2,"name":"Kun-Hoo Jeon","email":"","orcid":"","institution":"Yonsei University","correspondingAuthor":false,"prefix":"","firstName":"Kun-Hoo","middleName":"","lastName":"Jeon","suffix":""}],"badges":[],"createdAt":"2024-04-04 05:10:15","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-4215709/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-4215709/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1038/s41528-024-00332-0","type":"published","date":"2024-07-26T04:00:00+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":54952413,"identity":"82bcab95-c510-446e-a5f7-fd42863c02a7","added_by":"auto","created_at":"2024-04-19 06:05:39","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":519007,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eDesign of \u003c/strong\u003e\u003cem\u003e\u003cstrong\u003eis-\u003c/strong\u003e\u003c/em\u003e\u003cstrong\u003eOLEDs and characterization of the \u003c/strong\u003e\u003cem\u003e\u003cstrong\u003eis-\u003c/strong\u003e\u003c/em\u003e\u003cstrong\u003eETL and \u003c/strong\u003e\u003cem\u003e\u003cstrong\u003eis-\u003c/strong\u003e\u003c/em\u003e\u003cstrong\u003ecathode. a\u003c/strong\u003eSchematic of an \u003cem\u003eis-\u003c/em\u003eOLED structure from the \u003cem\u003eis-\u003c/em\u003eanode to the upper ETL. \u003cstrong\u003eb\u003c/strong\u003e \u003cem\u003eis-\u003c/em\u003eOLED fabrication process with sequential coating. \u003cstrong\u003ec\u003c/strong\u003eDevice structure and components of an \u003cem\u003eis-\u003c/em\u003eOLED. \u003cstrong\u003ed \u003c/strong\u003eSchematics of the \u003cem\u003eis-\u003c/em\u003eEML morphology change after ETL solvent coating. Based on the various analysis results, by adding Triton X into theETL solvent, the SY chains maintain an extended morphology after the \u003cem\u003eis-\u003c/em\u003eETL coating process, resulting in high stretchability. \u003cstrong\u003ee \u003c/strong\u003eSchematics of the \u003cem\u003eis-\u003c/em\u003ecathode morphology and electron conducting mechanism under stretching conditions.\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-4215709/v1/a324842b2f9f4c4cf6ce672d.png"},{"id":54952894,"identity":"827a781f-4d5a-432b-8f62-b927e92a2d33","added_by":"auto","created_at":"2024-04-19 06:21:39","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":238707,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eDesign and characterization of \u003c/strong\u003e\u003cem\u003e\u003cstrong\u003eis-\u003c/strong\u003e\u003c/em\u003e\u003cstrong\u003eETLs for highly stretchable \u003c/strong\u003e\u003cem\u003e\u003cstrong\u003eis-\u003c/strong\u003e\u003c/em\u003e\u003cstrong\u003efunctional layers. a\u003c/strong\u003e UV‒vis absorption spectra of \u003cem\u003eis-\u003c/em\u003eEMLs with various TX blending ratios, and solvent coating effect on the \u003cem\u003eis-\u003c/em\u003eEMLs. \u003cstrong\u003eb\u003c/strong\u003e UV-vis absorption spectra of is-EMLs before and after TX-blended solvent coating (TX1 = 1 mg ml\u003csup\u003e-1\u003c/sup\u003e, TX2 = 2 mg ml\u003csup\u003e-2\u003c/sup\u003e, TX4 = 4 mg ml\u003csup\u003e-1\u003c/sup\u003e). \u003cstrong\u003ec\u003c/strong\u003e Photoluminescence spectra of \u003cem\u003eis-\u003c/em\u003eEMLs before and after TX-blended solvent coating. \u003cstrong\u003ed\u003c/strong\u003e COS of \u003cem\u003eis-\u003c/em\u003eEMLs before and after TX-blended solvent coating. \u003cstrong\u003ee\u003c/strong\u003e COS of \u003cem\u003eis-\u003c/em\u003eETLs with various component ratios when coated on PDMS or \u003cem\u003eis-\u003c/em\u003eEMLs. \u003cstrong\u003ef \u003c/strong\u003eUPS intensity of \u003cem\u003eis-\u003c/em\u003eETL and Ag films with various TX ratios. \u003cstrong\u003eg \u003c/strong\u003eCurrent density of electron-only devices with various ETL component ratios. \u003cstrong\u003eh\u003c/strong\u003e Energy-level alignment diagram for the conventional OLED device with an\u003cem\u003e is-\u003c/em\u003eETL. \u003cstrong\u003ei \u003c/strong\u003e\u003cem\u003eV\u003c/em\u003e-\u003cem\u003eL\u003c/em\u003e curve, \u003cstrong\u003ej \u003c/strong\u003e\u003cem\u003eJ\u003c/em\u003e-\u003cem\u003eV\u003c/em\u003e curve, and \u003cstrong\u003ek \u003c/strong\u003e\u003cem\u003eε\u003c/em\u003e\u003csub\u003ec\u003c/sub\u003e-\u003cem\u003eL\u003c/em\u003e curve of the conventional OLED device with an\u003cem\u003e is-\u003c/em\u003eETL on a glass substrate.\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-4215709/v1/08e2e647a00e978bdb2553eb.png"},{"id":54952564,"identity":"22592a99-eb48-4929-a0b1-281214ce4c8e","added_by":"auto","created_at":"2024-04-19 06:13:39","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":561023,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eFabrication and characterization of \u003c/strong\u003e\u003cem\u003e\u003cstrong\u003eis-\u003c/strong\u003e\u003c/em\u003e\u003cstrong\u003eOLEDs. a\u003c/strong\u003e Schematics of the \u003cem\u003eis-\u003c/em\u003ecathode surface morphologies from a thin Ag to thick Ag film. \u003cstrong\u003eb\u003c/strong\u003eSheet resistance, stretchability of the \u003cem\u003eis-\u003c/em\u003ecathode, and luminance of the \u003cem\u003eis-\u003c/em\u003eOLED at various \u003cem\u003eis-\u003c/em\u003ecathode thicknesses. \u003cstrong\u003ec\u003c/strong\u003e Optimal Ag evaporation conditions for the \u003cem\u003eis-\u003c/em\u003ecathode. \u003cstrong\u003ed\u003c/strong\u003eResistance change in Ag cathode films with various thicknesses rangingfrom 30 nm to 70 nm during static stretching tests. \u003cstrong\u003ee\u003c/strong\u003e Resistance change in the 60 nm \u003cem\u003eis-\u003c/em\u003ecathode during cyclic stretching tests at 20% and 40% strain. \u003cstrong\u003ef\u003c/strong\u003e TEM cross-sectional image of the \u003cem\u003eis-\u003c/em\u003eOLED. \u003cstrong\u003eg\u003c/strong\u003e SEM image of the \u003cem\u003eis-\u003c/em\u003ecathode surface at 0% and 40% strain. \u003cstrong\u003eh\u003c/strong\u003e SEM image of the \u003cem\u003eis-\u003c/em\u003ecathode surface when stretched to 60% strain and released to 0% strain from 40% strain.\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-4215709/v1/da62df659d464eecad7decc2.png"},{"id":54952416,"identity":"f29ed305-f1f6-4035-bf17-eb80e5bc619b","added_by":"auto","created_at":"2024-04-19 06:05:39","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":734955,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eDevice performance of \u003c/strong\u003e\u003cem\u003e\u003cstrong\u003eis-\u003c/strong\u003e\u003c/em\u003e\u003cstrong\u003eOLEDs and deformable displays. a\u003c/strong\u003e Schematics of the \u003cem\u003eis-\u003c/em\u003eOLED structure and thickness. \u003cstrong\u003eb\u003c/strong\u003e Energy-level alignment diagram of the \u003cem\u003eis-\u003c/em\u003eOLED. \u003cstrong\u003ec\u003c/strong\u003e \u003cem\u003eJ\u003c/em\u003e-\u003cem\u003eV\u003c/em\u003e-\u003cem\u003eL\u003c/em\u003e curve of the \u003cem\u003eis-\u003c/em\u003eOLEDs. \u003cstrong\u003ed\u003c/strong\u003e Relative \u003cem\u003eL\u003c/em\u003e change (\u003cem\u003eL\u003c/em\u003e∙\u003cem\u003eL\u003c/em\u003e\u003csub\u003e0\u003c/sub\u003e\u003csup\u003e-1\u003c/sup\u003e) of the \u003cem\u003eis-\u003c/em\u003eOLEDs during static stretching tests when operated at 8 V. \u003cstrong\u003ee\u003c/strong\u003e \u003cem\u003eL\u003c/em\u003e∙\u003cem\u003eL\u003c/em\u003e\u003csub\u003e0\u003c/sub\u003e\u003csup\u003e-1\u003c/sup\u003e changes of the \u003cem\u003eis-\u003c/em\u003eOLEDs during 40% strain cyclic stretching tests. \u003cstrong\u003ef\u003c/strong\u003e Radar plot comparing the electroluminescence (EL) performance, stretchability, and fabrication complexity of \u003cem\u003eis-\u003c/em\u003eOLEDs produced using the sequential coating or lamination method. The fabrication complexity corresponds to the number of transfer and lamination processes during the \u003cem\u003eis-\u003c/em\u003eOLED fabrication process. \u003cstrong\u003eg \u003c/strong\u003eOptical images of the \u003cem\u003eis-\u003c/em\u003eOLEDs with an original emission area of 3.0 × 3.0 mm\u003csup\u003e2\u003c/sup\u003e operated under various strains. \u003cstrong\u003eh \u003c/strong\u003eOptical photographs of 3X2 \u003cem\u003eis-\u003c/em\u003eOLED array devices operated under various strains and deformations.\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-4215709/v1/b9aef12195fade622fd2b42d.png"},{"id":61211010,"identity":"86055233-0d69-4afb-8c1f-dd173fca26fa","added_by":"auto","created_at":"2024-07-27 07:09:45","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":3018857,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-4215709/v1/5947e9c2-5f9f-44ac-84af-6c083037d336.pdf"},{"id":54952418,"identity":"1c66bc38-ff71-4114-86f6-92783e989e24","added_by":"auto","created_at":"2024-04-19 06:05:41","extension":"docx","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":21712317,"visible":true,"origin":"","legend":"Supplementary Information","description":"","filename":"SupplementaryInformation.docx","url":"https://assets-eu.researchsquare.com/files/rs-4215709/v1/7cc5d35bcd657752c429197b.docx"}],"financialInterests":"(Not answered)","formattedTitle":"Intrinsically Stretchable OLEDs with a Designed Morphology-Sustainable Layer and Stretchable Metal Cathode","fulltext":[{"header":"INTRODUCTION","content":"\u003cp\u003eOrganic light-emitting diodes (OLEDs) are pivotal in current display technology because they offer advantages such as high energy efficiency and vibrant color reproduction.\u003csup\u003e1\u0026ndash;3\u003c/sup\u003e The recent shift from rigid devices toward soft electronics has sparked interest in intrinsically stretchable OLEDs (\u003cem\u003eis-\u003c/em\u003eOLEDs) that mimic skin-like properties.\u003csup\u003e4\u0026ndash;16\u003c/sup\u003e While significant progress has been made in enhancing the luminance and stretchability of \u003cem\u003eis-\u003c/em\u003eOLEDs, challenges persist in the manufacturing processes and intrinsically stretchable material design.\u003c/p\u003e \u003cp\u003ePrevious \u003cem\u003eis-\u003c/em\u003eOLED studies have focused on improving the stretchability of inherently rigid organic layers by blending various materials, such as Triton X-100 (TX) and poly(ethylene glycol)-block-poly(propylene glycol)-block-poly(ethylene glycol) (PEO-PPG-PEO) additives and polyurethane (PU) and polystyrene-block-polybutadiene-block-polystyrene (SBS) elastomers, which change the microstructure from rigid to stretchable.\u003csup\u003e12\u0026ndash;18\u003c/sup\u003e To fabricate \u003cem\u003eis-\u003c/em\u003eOLEDs with organic layers, solution coating, such as spin-coating, is usually performed. However, in many cases, the lack of solvent orthogonality between layers destroys the designed microstructure of the underlying layer, which significantly reduces the stretchability.\u003csup\u003e19,20\u003c/sup\u003e Hence, in previous works by others, lamination was used to build up the layers in \u003cem\u003eis-\u003c/em\u003eOLEDs. In Zhang et al., emissive layer (EML) and electron transport layer (ETL) surfaces were joined, and in Liu et al., the ETL and cathode surfaces were laminated. In many cases, a lack of solvent orthogonality occurred between the EML, ETL, and cathode layer. The lamination process includes alignment, interfacing, and hot pressing.\u003csup\u003e12\u0026ndash;15\u003c/sup\u003e During this process, misalignment and pressure-induced defects and voids induce insufficient layer contact, leading to delamination, dark spots, reduced fabrication yield, and decreased performance, especially under repeated stretching.\u003csup\u003e11\u003c/sup\u003e\u003c/p\u003e \u003cp\u003eIn conventional OLEDs, a metallic cathode is used due to the high density of free electrons and high charge carrier mobility. However, due to the inherent rigidity of metals, these cathodes were not considered as stretchable electrodes for use in \u003cem\u003eis-\u003c/em\u003eOLEDs. In previous works on \u003cem\u003eis-\u003c/em\u003eOLEDs, silver nanowires (AgNWs), graphene, and poly(2,3-dihydrothieno-1,4-dioxin)-poly(styrenesulfonate) (PEDOT:PSS) were used as stretchable cathodes, which are very limited candidates. AgNWs were embedded in an elastomer matrix to impart stretchability. Hence, they had to be fabricated on a separate substrate, followed by a physical lamination process onto the precoated organic layers.\u003csup\u003e13,15\u003c/sup\u003e Graphene cannot be directly synthesized on ETL surfaces; hence, its integration also involves a complex transfer process onto cathode surfaces, necessitating a subsequent lamination process.\u003csup\u003e13\u003c/sup\u003e While the PEDOT:PSS cathode can be directly spin-coated on organic surfaces, this approach risks damaging the underlayer due to the effect of the polar solvent on the ETL and the post-patterning process. As a result, PEDOT:PSS cathodes were also fabricated by a lamination process after the separate fabrication of \u003cem\u003eis-\u003c/em\u003ecathodes.\u003csup\u003e12\u003c/sup\u003e In summary, in addition to their inferior conductivity compared to that of conventional metallic cathodes, these materials inevitably require a manual lamination process during the fabrication of \u003cem\u003eis-\u003c/em\u003eOLEDs.\u003c/p\u003e \u003cp\u003eIn this study, we developed a hybrid fabrication process employing sequential solution coating and thermal evaporation, eliminating the need for a lamination process. We developed a newly designed morphology-sustainable \u003cem\u003eis-\u003c/em\u003eETL and a highly stretchable metallic \u003cem\u003eis-\u003c/em\u003ecathode. The \u003cem\u003eis-\u003c/em\u003eETL not only ensures a uniform surface but also sustains the designed morphology of the \u003cem\u003eis-\u003c/em\u003eEML, thereby enhancing the electrical and mechanical properties of \u003cem\u003eis-\u003c/em\u003eOLEDs. Furthermore, by adjusting the deposition conditions and controlling the thickness of the conventional brittle Ag metal film, we successfully fabricated a stretchable Ag electrode with high electrical conductivity. As a result, our device achieved a maximum total luminance of 3,151 cd m\u003csup\u003e-2\u003c/sup\u003e and a current efficiency of 5.4 cd A\u003csup\u003e-1\u003c/sup\u003e, maintaining approximately 50% performance at 70% strain and 80% performance after 300 cycles of stretching tests. This work explores new stretchable materials and fabrication processes and discusses potential challenges and advancements in mechanical and electrical properties, paving the way for the promising future of \u003cem\u003eis-\u003c/em\u003eOLED technology.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003cb\u003eFigure\u0026nbsp;1 Design of\u003c/b\u003e \u003cb\u003eis-\u003c/b\u003e\u003cb\u003eOLEDs and characterization of the\u003c/b\u003e \u003cb\u003eis-\u003c/b\u003e\u003cb\u003eETL and\u003c/b\u003e \u003cb\u003eis-\u003c/b\u003e\u003cb\u003ecathode. a\u003c/b\u003e Schematic of an \u003cem\u003eis-\u003c/em\u003eOLED structure from the \u003cem\u003eis-\u003c/em\u003eanode to the upper ETL. \u003cb\u003eb\u003c/b\u003e \u003cem\u003eis-\u003c/em\u003eOLED fabrication process with sequential coating. \u003cb\u003ec\u003c/b\u003e Device structure and components of an \u003cem\u003eis-\u003c/em\u003eOLED. \u003cb\u003ed\u003c/b\u003e Schematics of the \u003cem\u003eis-\u003c/em\u003eEML morphology change after ETL solvent coating. Based on the various analysis results, by adding Triton X into the ETL solvent, the SY chains maintain an extended morphology after the \u003cem\u003eis-\u003c/em\u003eETL coating process, resulting in high stretchability. \u003cb\u003ee\u003c/b\u003e Schematics of the \u003cem\u003eis-\u003c/em\u003ecathode morphology and electron conducting mechanism under stretching conditions.\u003c/p\u003e"},{"header":"RESULTS AND DISCUSSION","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e\n \u003ch2\u003eDesigns of intrinsically stretchable OLED\u003c/h2\u003e\n \u003cp\u003eFigure\u0026nbsp;1a shows a schematic image of the \u003cem\u003eis-\u003c/em\u003eOLEDs fabricated in this work. Figure\u0026nbsp;1b summarizes our sequential coating processes from the \u003cem\u003eis-\u003c/em\u003eanode to the upper ETL. As shown in Fig.\u0026nbsp;1c, for the \u003cem\u003eis-\u003c/em\u003eOLEDs, an intrinsically stretchable hole transport layer (\u003cem\u003eis-\u003c/em\u003eHTL) is formulated from PEDOT:PSS and the nonionic surfactant TX, and an intrinsically stretchable EML (\u003cem\u003eis-\u003c/em\u003eEML) is composed of a commercial EML, Super Yellow (SY) and TX.\u003csup\u003e16\u003c/sup\u003e TX affects the conformation and microstructure of PEDOT:PSS and SY, resulting in highly stretchable \u003cem\u003eis-\u003c/em\u003eHTL and \u003cem\u003eis-\u003c/em\u003eEML.\u003csup\u003e16\u003c/sup\u003e\u003c/p\u003e\n \u003cp\u003eAs illustrated in Fig.\u0026nbsp;1c, an intrinsically stretchable ETL (\u003cem\u003eis-\u003c/em\u003eETL) is spin-coated on the \u003cem\u003eis-\u003c/em\u003eEML. Prior research has employed materials such as polyethylenimine (PEI) and polyethyleneimine ethoxylated (PEIE) for \u003cem\u003eis-\u003c/em\u003eOLED ETLs due to their inherent stretchability and work function alignment properties, often in combination with electron-injecting materials such as ZnO, Cs\u003csub\u003e2\u003c/sub\u003eCO\u003csub\u003e3\u003c/sub\u003e, and poly(9,9-bis(3\u0026rsquo;-(N,N-dimethyl)-N-ethylammoinium-propyl-2,7-fluorene)-alt-2,7-(9,9-dioctylfluorene))dibromide (PFN-Br).\u003csup\u003e12\u0026ndash;16\u003c/sup\u003e Among them, PFN-Br stands out due to its superior electron injection and hole blocking capabilities, as well as its ability to facilitate a uniform surface. Nonetheless, the binary ETL composed of PFN-Br and PEIE has been found to offer limited stretchability and to adversely affect the underlying \u003cem\u003eis-\u003c/em\u003eEML during the solution coating process, highlighting the necessity for advanced material design.\u003c/p\u003e\n \u003cp\u003eMost solvents dissolve most nonionic surfactants, potentially altering the morphology of the organic layers including a nonionic surfactant during sequential coating. Furthermore, the mechanical and electrical properties of \u003cem\u003eis-\u003c/em\u003eEMLs are strongly affected by the morphology of the conjugated polymers.\u003csup\u003e12,16\u003c/sup\u003e Our study mitigated this by incorporating TX across all coating layers from the \u003cem\u003eis-\u003c/em\u003eHTL to \u003cem\u003eis-\u003c/em\u003eETL, ensuring the presence of TX on the underlayer surface to sustain the designed morphology of conjugated polymers, as shown in Fig.\u0026nbsp;1d. The incorporation of TX into the PFN-Br and PEIE matrix has been shown to enhance both the mechanical and electrical properties of the \u003cem\u003eis-\u003c/em\u003eOLED, leading to improved overall device performance.\u003c/p\u003e\n \u003cp\u003eFollowing the \u003cem\u003eis-\u003c/em\u003eETL coating process, an \u003cem\u003eis-\u003c/em\u003emetal cathode is developed using evaporation, as shown in Fig. 1e. Previous \u003cem\u003eis-\u003c/em\u003eOLED research employed stretchable electrode materials such as AgNWs, PEDOT:PSS, and graphene as cathodes.\u003csup\u003e12\u0026ndash;16\u003c/sup\u003e However, these stretchable electrodes often exhibit significant roughness, inferior electrical characteristics, or chemical instability. Furthermore, they require either a solution process or a complicated transfer process, which damages the underlying organic layers and complicates patterning.\u003csup\u003e11,21,22\u003c/sup\u003e Hence, the development of new stretchable electrode materials is imperative.\u003c/p\u003e\n \u003cp\u003eFor high-performance \u003cem\u003eis-\u003c/em\u003eOLEDs, electrode materials such as stretchable Al or Ag films are expected to be most effective because of their inherently high charge carrier density and mobility.\u003csup\u003e3\u003c/sup\u003e Such materials can be deposited by thermal evaporation, minimizing damage to the underlying organic layers, and are easily patterned. However, metal films inherently lack stretchability.\u003csup\u003e23\u0026ndash;25\u003c/sup\u003e To address this, modifying the interaction with the underlayer and adjusting the deposition conditions are crucial. We successfully fabricated a stretchable Ag electrode with high electrical conductivity by fine-tuning the deposition conditions and optimizing the thickness of the traditionally brittle silver metal film. The precisely adjusted evaporation conditions for the stretchable metal cathode resulted in only microcracks on the surface under stretching conditions, enabling efficient electron movement between the microcracks (Fig. 1e).\u003c/p\u003e\n \u003cp\u003e\u003cstrong\u003eFigure\u0026nbsp;2 Design and characterization of\u003c/strong\u003e \u003cstrong\u003eis-\u003c/strong\u003e\u003cstrong\u003eETLs for highly stretchable\u003c/strong\u003e \u003cstrong\u003eis-\u003c/strong\u003e\u003cstrong\u003efunctional layers. a\u003c/strong\u003e UV‒vis absorption spectra of \u003cem\u003eis-\u003c/em\u003eEMLs with various TX blending ratios, and solvent coating effect on the \u003cem\u003eis-\u003c/em\u003eEMLs. \u003cstrong\u003eb\u003c/strong\u003e UV-vis absorption spectra of is-EMLs before and after TX-blended solvent coating (TX1\u0026thinsp;=\u0026thinsp;1 mg ml\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, TX2\u0026thinsp;=\u0026thinsp;2 mg ml\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e, TX4\u0026thinsp;=\u0026thinsp;4 mg ml\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e). \u003cstrong\u003ec\u003c/strong\u003e Photoluminescence spectra of \u003cem\u003eis-\u003c/em\u003eEMLs before and after TX-blended solvent coating. \u003cstrong\u003ed\u003c/strong\u003e COS of \u003cem\u003eis-\u003c/em\u003eEMLs before and after TX-blended solvent coating. \u003cstrong\u003ee\u003c/strong\u003e COS of \u003cem\u003eis-\u003c/em\u003eETLs with various component ratios when coated on PDMS or \u003cem\u003eis-\u003c/em\u003eEMLs. \u003cstrong\u003ef\u003c/strong\u003e UPS intensity of \u003cem\u003eis-\u003c/em\u003eETL and Ag films with various TX ratios. \u003cstrong\u003eg\u003c/strong\u003e Current density of electron-only devices with various ETL component ratios. \u003cstrong\u003eh\u003c/strong\u003e Energy-level alignment diagram for the conventional OLED device with an \u003cem\u003eis-\u003c/em\u003eETL. \u003cstrong\u003ei\u003c/strong\u003e \u003cem\u003eV\u003c/em\u003e-\u003cem\u003eL\u003c/em\u003e curve, \u003cstrong\u003ej\u003c/strong\u003e \u003cem\u003eJ\u003c/em\u003e-\u003cem\u003eV\u003c/em\u003e curve, and \u003cstrong\u003ek\u003c/strong\u003e \u003cem\u003e\u0026epsilon;\u003c/em\u003e\u003csub\u003ec\u003c/sub\u003e-\u003cem\u003eL\u003c/em\u003e curve of the conventional OLED device with an \u003cem\u003eis-\u003c/em\u003eETL on a glass substrate.\u003c/p\u003e\n\u003c/div\u003e\n\u003ch3\u003eDesigned morphology sustainable electron transport layer\u003c/h3\u003e\n\u003cp\u003ePFN-Br, distinguished by its high lowest unoccupied molecular orbital (LUMO) level of 2.7 eV and low highest occupied molecular orbital (HOMO) level of 5.6 eV, was selected as the \u003cem\u003eis-\u003c/em\u003eETL (Fig.\u0026nbsp;1c). It offers significant advantages for electron injection and hole blocking in OLED structures.\u003csup\u003e12,26\u003c/sup\u003e Furthermore, the addition of PEIE contributes to a notable increase in the stretchability of the material, reaching approximately 70% strain (Supplementary Fig.\u0026nbsp;1). However, the stretchability of PFN-Br:PEIE is lower than the 80% crack onset strain (COS) of the \u003cem\u003eis-\u003c/em\u003eEML. Additionally, when PEIE or PFN-Br:PEIE solution is coated on the \u003cem\u003eis-\u003c/em\u003eEML, a significant reduction in the COS to 40% occurs (Supplementary Fig.\u0026nbsp;2). This reduction suggests that the impact on stretchability is due not only to the intrinsic properties of the ETL but also to changes in the underlying \u003cem\u003eis-\u003c/em\u003eEML layer.\u003c/p\u003e\n\u003cp\u003eFor the \u003cem\u003eis-\u003c/em\u003eEML, TX mixed with SY-conjugated polymers (Fig.\u0026nbsp;1c) alters the morphology of the polymers from coiled to extended, resulting in high stretchability and electrical properties.\u003csup\u003e16\u003c/sup\u003e This morphological change is evident through the redshifted absorbance (Abs), blueshifted photoluminescence (PL), and changes in the atomic force microscopy (AFM) surface phase (Fig.\u0026nbsp;2a, Supplementary Figs.\u0026nbsp;3 and 4). Here, we coated various solvents on \u003cem\u003eis-\u003c/em\u003eEMLs to investigate the effect of dissolution of \u003cem\u003eis-\u003c/em\u003eEMLs in the solvent on the changes in the conformation and morphology of the \u003cem\u003eis-\u003c/em\u003eEMLs (Fig.\u0026nbsp;2a). Regardless of the TX concentration in the SY and ETL materials, applying a solvent coating on the \u003cem\u003eis-\u003c/em\u003eEML to coat the \u003cem\u003eis-\u003c/em\u003eETL reverts the Abs, PL, and phase changes to those of pristine SY (Supplementary Figs.\u0026nbsp;2, 3, and 4).\u003c/p\u003e\n\u003cp\u003eSince TX, a nonionic surfactant, is soluble in most organic solvents, we can anticipate that the characteristics of the EML may change when the TX present on the SY surface is washed away. Therefore, to maintain the morphology of the \u003cem\u003eis-\u003c/em\u003eEML, TX was also incorporated into the ETL. This addition ensures that the designed morphology from the HTL to the ETL is maintained during the continuous coating process. Figures\u0026nbsp;2b and 2c confirm that mixing TX with the solvent sustains the redshifted Abs and blueshifted PL peaks after coating, akin to the behavior of the \u003cem\u003eis-\u003c/em\u003eEML. Moreover, increasing the TX concentration better sustain the \u003cem\u003eis-\u003c/em\u003eEML Abs and PL peaks up to 4 mg ml\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e.\u003c/p\u003e\n\u003cp\u003eFigure\u0026nbsp;2d shows the effect of TX on the COS of the \u003cem\u003eis-\u003c/em\u003eEML (Supplementary Fig.\u0026nbsp;2, Supplementary Fig.\u0026nbsp;9). Mixing SY with TX increases the COS. Applying the solvent coating alone decreases the COS to 40%, whereas the solvent containing TX yields a COS of 60% at 1 mg ml\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, 80% at 2 mg ml\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, and 90% at 4 mg ml\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e. These findings suggest that the TX-blended solvent maintains the \u003cem\u003eis-\u003c/em\u003eEML morphology, ensuring high stretchability. Therefore, coating of an ETL solution with TX is crucial for preserving the extended morphology of the \u003cem\u003eis-\u003c/em\u003eEML.\u003c/p\u003e\n\u003cp\u003eFigure\u0026nbsp;2e shows the mechanical characteristics of the ternary blends of PFN-Br, PEIE, and TX. TX increases the COS of the \u003cem\u003eis-\u003c/em\u003eETL by increasing the free volume within the material and decreasing the crystallinity of the conjugated polymer (Supplementary Fig.\u0026nbsp;1).\u003csup\u003e16,26\u003c/sup\u003e Hence, the ternary blend of the \u003cem\u003eis-\u003c/em\u003eETL with a ratio of 2:2:2 inherently exhibits high stretchability and is capable of withstanding up to 100% COS. When this \u003cem\u003eis-\u003c/em\u003eETL is applied over the \u003cem\u003eis-\u003c/em\u003eEML, the COS increases as the ratio of TX increases, matching the COS of the \u003cem\u003eis-\u003c/em\u003eEML itself. The introduction of TX into the PFN-Br:PEIE ETL has dual effects: providing high stretchability of the \u003cem\u003eis-\u003c/em\u003eETL and sustaining the designed morphology of the \u003cem\u003eis-\u003c/em\u003eEML. This stretchability alignment between the \u003cem\u003eis-\u003c/em\u003eETL and \u003cem\u003eis-\u003c/em\u003eEML is a significant achievement, ensuring that the overall device can maintain its structural integrity and functional performance even under considerable mechanical strain. Furthermore, the ternary blended \u003cem\u003eis-\u003c/em\u003eETL shows a uniform surface morphology, as shown in Supplementary Fig.\u0026nbsp;10.\u003c/p\u003e\n\u003cp\u003eFigure\u0026nbsp;2f shows the electrical properties of the \u003cem\u003eis-\u003c/em\u003eETLs. Ultraviolet photoelectron spectroscopy (UPS) measurements, based on the TX blending ratio, reveal that the work function of 4.8 eV for the pristine Ag film decreases to 3.3 eV following coating with a PFN-Br:PEIE (2:2) solution. Additional blending of the ETL with TX results in work functions of 3.25 eV for a 2:2:1 ratio and 3.35 eV for a 2:2:2 ratio, indicating similar electron injection characteristics (Supplementary Fig.\u0026nbsp;12, Supplementary Table\u0026nbsp;1). Triton X is an electrical insulator, but we estimate that the dipole of the nonionic surfactant TX lowers the work functions of PEIE and PFN-Br.\u003c/p\u003e\n\u003cp\u003eAs shown in Fig.\u0026nbsp;2g, we fabricated electron-only devices using the \u003cem\u003eis-\u003c/em\u003eETLs, the detailed structure of which is presented in Supplementary Fig.\u0026nbsp;13. Compared to PFN-Br, the PFN-Br:PEIE ETL exhibits a higher current density. Furthermore, as the TX blending ratio increases, the electron current density correspondingly increases. This finding implies that the TX-blended \u003cem\u003eis-\u003c/em\u003eETL improves the electron transport properties by maintaining the extended morphology of the \u003cem\u003eis-\u003c/em\u003eEML. Then, we fabricated devices with a conventional OLED structure using the \u003cem\u003eis-\u003c/em\u003eETLs (Fig.\u0026nbsp;2h). Figure\u0026nbsp;2i demonstrates the improved performance obtained with the TX-blended \u003cem\u003eis-\u003c/em\u003eETLs compared to that obtained with the 2:2 ratio, and the increase in the efficiency is shown in Fig.\u0026nbsp;2k. Hence, the TX-blended \u003cem\u003eis-\u003c/em\u003eETLs not only exhibit inherently high mechanical and electrical properties but also help sustain the designed morphology of the \u003cem\u003eis-\u003c/em\u003eEML, thereby enhancing its mechanical and electrical characteristics. Although the 2:2:1 ratio results in a slightly better performance, we chose a 2:2:2 ratio of the \u003cem\u003eis-\u003c/em\u003eETL for the \u003cem\u003eis-\u003c/em\u003eOLED fabrication to enhance the \u003cem\u003eis-\u003c/em\u003eEML stretchability.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFig. 3 Fabrication and characterization of \u003cem\u003eis-\u003c/em\u003eOLEDs. a\u003c/strong\u003e Schematics of\u0026nbsp;the \u003cem\u003eis-\u003c/em\u003ecathode surface morphologies from a thin Ag to thick Ag film. \u003cstrong\u003eb\u003c/strong\u003e Sheet resistance, stretchability of\u0026nbsp;the \u003cem\u003eis-\u003c/em\u003ecathode, and\u0026nbsp;luminance\u0026nbsp;of\u0026nbsp;the \u003cem\u003eis-\u003c/em\u003eOLED at various \u003cem\u003eis-\u003c/em\u003ecathode\u0026nbsp;thicknesses. \u003cstrong\u003ec\u003c/strong\u003e Optimal Ag evaporation\u0026nbsp;conditions\u0026nbsp;for the \u003cem\u003eis-\u003c/em\u003ecathode. \u003cstrong\u003ed\u003c/strong\u003e Resistance change\u0026nbsp;in\u0026nbsp;Ag cathode\u0026nbsp;films\u0026nbsp;with various\u0026nbsp;thicknesses ranging\u0026nbsp;from 30 nm to 70 nm during static stretching tests. \u003cstrong\u003ee\u003c/strong\u003e Resistance change\u0026nbsp;in\u0026nbsp;the 60 nm \u003cem\u003eis-\u003c/em\u003ecathode during cyclic stretching tests at 20% and 40% strain. \u003cstrong\u003ef\u003c/strong\u003e TEM cross-sectional image of the \u003cem\u003eis-\u003c/em\u003eOLED.\u0026nbsp;\u003cstrong\u003eg\u003c/strong\u003e SEM image of the \u003cem\u003eis-\u003c/em\u003ecathode surface at 0% and 40% strain. \u003cstrong\u003eh\u003c/strong\u003e SEM image of the \u003cem\u003eis-\u003c/em\u003ecathode surface when stretched to 60% strain and released to 0% strain from 40% strain.\u003c/p\u003e\n\u003cdiv id=\"Sec5\" class=\"Section2\"\u003e\n \u003ch2\u003eIntrinsically stretchable Ag metal cathode\u003c/h2\u003e\n \u003cp\u003eTo render the Ag film stretchable, we optimized the deposition parameters (evaporation rate and thickness) and the substrate. The structure and properties of the film largely depend on the substrate. Since our cathodes are positioned on top of the devices rather than directly above the elastomer substrate, options for the deposition surface are more constrained than those in previously reported stretchable metal studies.\u003csup\u003e27\u0026ndash;30\u003c/sup\u003e The deposition surface must have (\u003cspan class=\"CitationRef\"\u003e1\u003c/span\u003e) a smooth surface, (\u003cspan class=\"CitationRef\"\u003e2\u003c/span\u003e) high compatibility (adhesion) with Ag atoms, and (\u003cspan class=\"CitationRef\"\u003e3\u003c/span\u003e) appropriate energy levels for electron injection. PFN-Br:PEIE:TX meets all these requirements because of its low surface roughness and adequate energy level (Supplementary Fig.\u0026nbsp;10 and Fig.\u0026nbsp;2f ). Additionally, the amine groups in PEIE are compatible with Ag atoms through coordination bonds, functioning as seed layers for ultrathin Ag films.\u003csup\u003e23\u003c/sup\u003e\u003c/p\u003e\n \u003cp\u003eThe evaporation rate and thickness were optimized to achieve both good optoelectrical properties and stretchability. Ag films deposited on the elastomer substrate form three-dimensional islands according to the Volmer\u0026ndash;Weber growth mechanism and eventually connect to form a continuous film with increasing thickness (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003ea).\u003csup\u003e31\u003c/sup\u003e A greater thickness ensures high bulk conductivity but can also make the film brittle. A high evaporation rate leads to continuous films by suppressing Volmer\u0026ndash;Weber growth, while a lower rate enhances stretchability due to the interlocking interface between the metal and substrate and the optimal grain size.\u003csup\u003e29,32\u003c/sup\u003e Therefore, we aimed to scale down the deposition thickness and rate until superior optoelectrical properties could be maintained (Figs.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003eb, c, and d).\u003c/p\u003e\n \u003cp\u003eWe selected Ag films with a thickness of 60 nm deposited at a rate of 1 \u0026Aring; s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e as our stretchable cathode. To determine the optimal deposition parameters, we fabricated our stretchable cathode on the \u003cem\u003eis\u003c/em\u003e-OLEDs (Fig.\u0026nbsp;1a), We then characterized its optoelectrical properties, focusing on maximum luminance (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003eb, c) and cathode conductivity under static and cyclic stretching conditions (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003ed, e). The conductivity rapidly decreases below 40 nm in thickness due to the poor connectivity between Ag grains (Figs.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003eb, d and Supplementary Fig.\u0026nbsp;14). Ag films thicker than 60 nm have high conductivity and show a superior luminance of over 3,200 cd m\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e when used as a cathode in \u003cem\u003eis-\u003c/em\u003eOLEDs but cannot endure strains above 60% due to the brittle nature of the dense, continuous Ag grains (Figs.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003eb, d, Supplementary Fig.\u0026nbsp;14, and Supplementary Fig.\u0026nbsp;16). A 60 nm stretchable cathode exhibits a low sheet resistance of 6 Ω sq\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e and a maximum luminance of more than 2,300 cd m\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e and maintains a resistance change of R R\u003csub\u003e0\u003c/sub\u003e\u0026thinsp;\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e \u0026lt; 10 under 70% strain, simultaneously ensuring high electrical conductivity and mechanical stretchability (Figs.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003eb, c, d, and Supplementary Fig.\u0026nbsp;16). Additionally, the material maintains its conductivity during 200 cycles of 40% strain stretching (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003ee).\u003c/p\u003e\n \u003cp\u003eWe investigated the relationship between the microstructures and electrical properties of Ag films via scanning electron microscopy (SEM), transmission electron microscopy (TEM), and time-of-flight secondary ion mass spectrometry (TOF-SIMS). Partially connected morphologies of Ag grains are observed, as shown in Figs. \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003ef and g. The actual grain size of the deposited film is approximately 35 nm (note that we describe the deposition thickness values measured by a quartz crystal sensor during thermal evaporation). Due to the slow deposition process, an intermixed region of Ag and organic layers is observed in the TOF-SIMS and TEM cross-section images (Fig. \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003ef and Supplementary Figs. 17\u0026ndash;19). No observable channel cracks appear on the film in the optical microscopy (OM) images until 60% strain (Supplementary Fig. 20). Instead, microcracks develop throughout the film during the stretching process. Under stretching, strain is released by widening of preexisting cracks while conducting paths are preserved through connected grains (Figs. \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003ed, g, and h). The cracks reversibly close after strain release; thus, the Ag cathode also shows high electrical and mechanical stability under cyclic stretching (Figs. \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003ee, h and Supplementary Fig.\u0026nbsp;23).\u003c/p\u003e\n \u003cp\u003eOur stretchability of the Ag cathode seems to be based on two unique structural features of \u003cem\u003eis-\u003c/em\u003eOLEDs. First, the multilayers under the cathode (from the \u003cem\u003eis-\u003c/em\u003eHTL to \u003cem\u003eis-\u003c/em\u003eETL) provide a gradient in the Young\u0026rsquo;s modulus between the soft elastomer substrate and the stiff metal cathodes. This enhances the stretchability of the cathode compared to structures without multilayer configurations (Supplementary Fig.\u0026nbsp;24). Second, the partially interconnected Ag morphologies allow additional layers to be overcoated on the cathodes. We overcoated cesium carbonate-doped PEIE (d-PEIE) on a Ag cathode, which possesses superior electron injection properties.\u003csup\u003e33\u003c/sup\u003e If d-PEIE is placed between our \u003cem\u003eis-\u003c/em\u003eETL and \u003cem\u003eis-\u003c/em\u003ecathode, it could hinder electron transport due to its electrically insulating nature and disrupt the intended Ag nucleation and growth processes by altering the surface properties. However, by applying it as an overcoating layer above the cathode, it primarily influences the lowering of the energy barrier for electron injection through channels within Ag films. Therefore, the d-PEIE overcoating layer was considered to contribute to the high luminance and improved stretchability of the \u003cem\u003eis-\u003c/em\u003eOLEDs (Supplementary Fig. 25).\u003c/p\u003e\n \u003cp\u003e\u003cstrong\u003eFigure\u0026nbsp;4 Device performance of\u003c/strong\u003e \u003cstrong\u003eis-\u003c/strong\u003e\u003cstrong\u003eOLEDs and deformable displays. a\u003c/strong\u003e Schematics of the \u003cem\u003eis-\u003c/em\u003eOLED structure and thickness. \u003cstrong\u003eb\u003c/strong\u003e Energy-level alignment diagram of the \u003cem\u003eis-\u003c/em\u003eOLED. \u003cstrong\u003ec\u003c/strong\u003e \u003cem\u003eJ\u003c/em\u003e-\u003cem\u003eV\u003c/em\u003e-\u003cem\u003eL\u003c/em\u003e curve of the \u003cem\u003eis-\u003c/em\u003eOLEDs. \u003cstrong\u003ed\u003c/strong\u003e Relative \u003cem\u003eL\u003c/em\u003e change (\u003cem\u003eL\u003c/em\u003e∙\u003cem\u003eL\u003c/em\u003e\u003csub\u003e0\u003c/sub\u003e\u0026thinsp;\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) of the \u003cem\u003eis-\u003c/em\u003eOLEDs during static stretching tests when operated at 8 V. \u003cstrong\u003ee\u003c/strong\u003e \u003cem\u003eL\u003c/em\u003e∙\u003cem\u003eL\u003c/em\u003e\u003csub\u003e0\u003c/sub\u003e\u0026thinsp;\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e changes of the \u003cem\u003eis-\u003c/em\u003eOLEDs during 40% strain cyclic stretching tests. \u003cstrong\u003ef\u003c/strong\u003e Radar plot comparing the electroluminescence (EL) performance, stretchability, and fabrication complexity of \u003cem\u003eis-\u003c/em\u003eOLEDs produced using the sequential coating or lamination method. The fabrication complexity corresponds to the number of transfer and lamination processes during the \u003cem\u003eis-\u003c/em\u003eOLED fabrication process. \u003cstrong\u003eg\u003c/strong\u003e Optical images of the \u003cem\u003eis-\u003c/em\u003eOLEDs with an original emission area of 3.0 \u0026times; 3.0 mm\u003csup\u003e2\u003c/sup\u003e operated under various strains. \u003cstrong\u003eh\u003c/strong\u003e Optical photographs of 3X2 \u003cem\u003eis-\u003c/em\u003eOLED array devices operated under various strains and deformations.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec6\" class=\"Section2\"\u003e\n \u003ch2\u003eFully intrinsically stretchable OLED\u003c/h2\u003e\n \u003cp\u003eAfter detailed characterization of the \u003cem\u003eis-\u003c/em\u003eETL and \u003cem\u003eis-\u003c/em\u003ecathode, \u003cem\u003eis-\u003c/em\u003eOLEDs were fabricated. The fabrication involved sequential coating of the \u003cem\u003eis-\u003c/em\u003eETL, \u003cem\u003eis-\u003c/em\u003ecathode, and an upper ETL over the \u003cem\u003eis-\u003c/em\u003eEML and \u003cem\u003eis-\u003c/em\u003eHTL based on AgNW-embedded polydimethylsiloxane (PDMS). The structural design and energy-level alignment of these devices are illustrated in Figs.\u0026nbsp;4a and 4b. Figure\u0026nbsp;4c shows the characteristic current density\u0026ndash;voltage\u0026ndash;luminance (\u003cem\u003eJ\u003c/em\u003e-\u003cem\u003eV\u003c/em\u003e-\u003cem\u003eL\u003c/em\u003e) curves for the \u003cem\u003eis-\u003c/em\u003eOLEDs. These devices display a turn-on voltage of 6 V, achieving a maximum brightness of approximately 2,340 cd m\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e at 9 V, for a measurement taken from the AgNW side. The maximum current efficiency recorded for this side is approximately 4.2 cd A\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e.\u003c/p\u003e\n \u003cp\u003eOn the opposite side, where a semitransparent Ag cathode film is used, the performance is approximately 40% of that observed on the AgNW side. This side shows a luminance of 811 cd m\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e and a current efficiency of 1.2 cd A\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e. The diminished performance on this Ag side is primarily due to its lower transmittance and reflectance compared to those on the AgNW side. When considering the total performance of the device, combining both the anode and cathode sides, the overall luminance reaches an impressive 3,151 cd m\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e, with a corresponding current efficiency of 5.4 cd A\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e. This indicates the high overall performance of the \u003cem\u003eis-\u003c/em\u003eOLEDs, demonstrating the effectiveness of the sequential coating process and the synergy between the \u003cem\u003eis-\u003c/em\u003eETL and \u003cem\u003eis-\u003c/em\u003ecathode in enhancing the device efficiency and brightness.\u003c/p\u003e\n \u003cp\u003eThe stretchability of the \u003cem\u003eis-\u003c/em\u003eOLEDs was tested to evaluate their durability and adaptability under mechanical stress. These tests involved both static and cyclic stretching tests, with the outcomes presented in Fig.\u0026nbsp;4d, focusing on the relative luminance change in response to various levels of strain at 8 V. At 0% strain, the average luminance across five samples was recorded as 791 cd m\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e. As the strain increases, the devices demonstrate remarkable resilience. Up to a 20% strain at 8 V, there is a negligible reduction in performance, indicating a high level of stretchability. However, as the strain is further increased, the luminance gradually decreases. At 40% strain, the devices maintain approximately 75% of their original luminance. This value decreases to approximately 55% at 60% strain and further decreases to approximately 45% at 70% strain. These results are comparable to those achieved by devices using stretchable electrodes such as AgNWs and PEDOT:PSS.\u003csup\u003e12\u0026ndash;14,16\u003c/sup\u003e This performance underlines the significant potential of metal-based stretchable cathodes in future applications.\u003c/p\u003e\n \u003cp\u003eFigure\u0026nbsp;4d illustrates the changes in the performance of the \u003cem\u003eis-\u003c/em\u003eOLEDs under cyclic stretching conditions at 40% strain. A special jig for the cyclic test is shown in Supplementary Fig.\u0026nbsp;26. In the early stages of the cyclic stretching test, specifically up to 50 cycles, the performance of the devices decreases, and the luminance decreases to approximately 85% of its original value. However, when the test is extended to 300 cycles, the luminance of the devices remarkably stabilizes, maintaining approximately 80% of the initial value. This indicates a significantly greater cyclic stretchability than that reported in previous studies using lamination processes, which exhibited a performance below 80% after 100 cycles at 15% and 40% strain.\u003csup\u003e12,14\u003c/sup\u003e Notably, our devices maintain stable performance for up to 300 cycles, surpassing the 200 cycles achieved in similar studies using sequential coating.\u003csup\u003e16\u003c/sup\u003e\u003c/p\u003e\n \u003cp\u003eAfter the cyclic test, the top surface of the \u003cem\u003eis-\u003c/em\u003eOLEDs was observed via SEM (Supplementary Fig.\u0026nbsp;27). This analysis reveals the formation of microcracks on the surfaces of the \u003cem\u003eis-\u003c/em\u003eOLEDs due to stretching. However, microcracks and crack closure are vital characteristics, as they allow for continued flow and injection of charge across the affected areas, ensuring sustained device functionality. This resilience of the \u003cem\u003eis-\u003c/em\u003eOLEDs under cyclic stretching, particularly their ability to maintain a high level of performance after 300 cycles at 40% strain, is an significant improvement over previous devices.\u003csup\u003e12\u0026ndash;14,16\u003c/sup\u003e These results demonstrate the superior mechanical and electrical properties of the \u003cem\u003eis-\u003c/em\u003eETL and \u003cem\u003eis-\u003c/em\u003emetal cathode compared to those achieved with conventional stretchable electrodes.\u003csup\u003e12\u0026ndash;14,16\u003c/sup\u003e\u003c/p\u003e\n \u003cp\u003eFigure\u0026nbsp;4f presents a radar plot comparing the performance and fabrication complexity of \u003cem\u003eis-\u003c/em\u003eOLEDs made using traditional lamination processes and our sequentially coated \u003cem\u003eis-\u003c/em\u003eOLEDs (Supplementary Table\u0026nbsp;2). While the luminance and efficiency are similar or slightly lower than those achieved with lamination methods, our \u003cem\u003eis-\u003c/em\u003eOLEDs exhibit higher static stretchability and notably superior cyclic stretchability. In terms of fabrication complexity, our approach shows the most advantageous characteristics, indicative of the reduced need for lamination and transfer processes during the fabrication process. The sequentially coated \u003cem\u003eis-\u003c/em\u003eOLEDs, made using the designed morphology-sustainable \u003cem\u003eis-\u003c/em\u003eETL and \u003cem\u003eis-\u003c/em\u003emetal cathode, simplify the traditionally complex processes associated with lamination methods, achieving high levels of cyclic stretchability.\u003c/p\u003e\n \u003cp\u003eFigure\u0026nbsp;4g depicts the light emitted from an \u003cem\u003eis-\u003c/em\u003eOLED when it is stretched. The image shows that the device emits light consistently across its entire surface area both in a neutral state (0% strain) and under significant stretching (up to 70% strain). Further expanding on the capabilities of these devices, Fig.\u0026nbsp;4h shows a 3\u0026times;2 array device fabricated using the \u003cem\u003eis-\u003c/em\u003eOLEDs subjected to stretching. The detailed structure of this array is illustrated in Supplementary Fig.\u0026nbsp;28. This array device shows stable light emission up to 50% strain. Furthermore, the array device also demonstrates resilience to various other forms of deformation, including bending, folding, and crumpling. This ability to maintain stable light emission even under deformation conditions is a testament to the mechanical robustness and versatility of these devices.\u003c/p\u003e\n \u003cp\u003eIn summary, this study has made significant strides in the field of \u003cem\u003eis-\u003c/em\u003eOLEDs by innovating and developing new stretchable component materials, such as designed morphology-sustainable \u003cem\u003eis-\u003c/em\u003eETLs and \u003cem\u003eis-\u003c/em\u003eAg metal cathodes. These advancements have been crucial in enhancing the overall performance of \u003cem\u003eis-\u003c/em\u003eOLEDs. The meticulously adjusted formulation of PFN-Br, PEIE, and TX blended into the \u003cem\u003eis-\u003c/em\u003eETL has been instrumental in enhancing both the mechanical and electrical properties of \u003cem\u003eis-\u003c/em\u003eOLEDs. The blending of PFN-Br and PEIE has demonstrated the ability to form a stretchable matrix simultaneously exhibiting high electron injection characteristics. Additionally, the incorporation of TX into this blend has been effective in sustaining the morphology of the underlying \u003cem\u003eis-\u003c/em\u003eEML, leading to simultaneous improvements in both the mechanical and electrical properties of the \u003cem\u003eis-\u003c/em\u003eEML and \u003cem\u003eis-\u003c/em\u003eETL. The \u003cem\u003eis-\u003c/em\u003ecathode, engineered under controlled deposition conditions, has achieved significant advancements in terms of morphology control and adhesion with the \u003cem\u003eis-\u003c/em\u003eETL. This has led to the creation of a metal cathode that not only is highly stretchable but also maintains excellent electrical conductivity, which is a critical attribute for effective \u003cem\u003eis-\u003c/em\u003eOLED operation.\u003c/p\u003e\n \u003cp\u003eFurthermore, this research represents a departure from more complex lamination techniques through rational material engineering and optimized device construction. This approach significantly contributes to simplifying the fabrication process, making it more accessible for the development of next-generation stretchable optoelectronic devices. While acknowledging that the current performance of these \u003cem\u003eis-\u003c/em\u003eOLEDs still lags behind that of conventional OLEDs, this study underscores the immense potential for future enhancements. In particular, the prospects of improving the performance through fine-tuning aspects such as the Ag stretchable cathode as well as the thickness and combination of the ETL are promising. Looking ahead, the continued development and utilization of stretchable metallic cathodes are expected to lead to significant performance improvements in \u003cem\u003eis-\u003c/em\u003eOLEDs, opening up new possibilities and applications in the realm of flexible and wearable electronics.\u003c/p\u003e\n\u003c/div\u003e"},{"header":"METHODS","content":"\u003cp\u003e \u003cb\u003ePreparation of\u003c/b\u003e \u003cb\u003eis-\u003c/b\u003e\u003cb\u003eEML and\u003c/b\u003e \u003cb\u003eis-\u003c/b\u003e\u003cb\u003eHTL\u003c/b\u003e\u003c/p\u003e \u003cp\u003eFor preparation of the \u003cem\u003eis-\u003c/em\u003eEML solution, TX (Sigma‒Aldrich) was first dissolved in toluene at a concentration of 2.5 mg ml\u003csup\u003e-1\u003c/sup\u003e. Then, SY (PDY-132, Sigma‒Aldrich) was blended in the TX-dissolved toluene at a concentration of 5 mg ml\u003csup\u003e-1\u003c/sup\u003e. The blended solution was stirred at 300 rpm for 12 h at 60 ℃. After stirring, the \u003cem\u003eis-\u003c/em\u003eEML was spin-coated on the \u003cem\u003eis-\u003c/em\u003eHTL composed of a 1:1 solution of PEDOT:PSS (Al 4083, Heraeus Clevios) and isopropyl alcohol (IPA) with 5 wt% TX.\u003c/p\u003e \u003cp\u003e \u003cb\u003ePreparation of\u003c/b\u003e \u003cb\u003eis-\u003c/b\u003e\u003cb\u003eETLs and Upper ETL\u003c/b\u003e\u003c/p\u003e \u003cp\u003eFor the \u003cem\u003eis-\u003c/em\u003eETL and upper ETL, a PFN-Br:PEIE:TX solution and a d-PEIE solution were prepared. For the d-PEIE solution, PEIE (Sigma‒Aldrich, 37 wt%) and Cs\u003csub\u003e2\u003c/sub\u003eCO\u003csub\u003e3\u003c/sub\u003e (Sigma‒Aldrich) were codissolved in 2-methoxyethanol (for which the weight ratio of PEIE to Cs\u003csub\u003e2\u003c/sub\u003eCO\u003csub\u003e3\u003c/sub\u003e was 10:1) at a 4 wt% concentration. After sonication of the d-PEIE solution via ultrasonication, the d-PEIE solution was stirred at 80\u0026deg;C for 12 hours. For the PFN-Br:PEIE:TX solution, PEIE and TX were dissolved in methanol at a concentration of 4 mg ml\u003csup\u003e-1\u003c/sup\u003e. Then, 2 mg of PFN-Br (Ossila) was dissolved in 0.5 ml of PEIE and 0.25 ml of a TX-blended solution (weight ratio of PFN-Br:PEIE:TX of 2:2:1) or 0.5 ml of a TX-blended solution (weight ratio of PFN-Br:PEIE:TX of 2:2:2).\u003c/p\u003e \u003cp\u003e \u003cb\u003eMechanical characterization of\u003c/b\u003e \u003cb\u003eis-\u003c/b\u003e\u003cb\u003eEMLs\u003c/b\u003e, \u003cb\u003eis-\u003c/b\u003e\u003cb\u003eETLs, and\u003c/b\u003e \u003cb\u003eis-\u003c/b\u003e\u003cb\u003ecathode\u003c/b\u003e\u003c/p\u003e \u003cp\u003eFor the stretchable substrate, a PDMS substrate was cured on a polyethylene terephthalate (PET) substrate. The PDMS (Sylgard 184, Dow Corning) was prepared by mixing the base and agent at a 10:1 weight ratio and spin-coating the mixture on the PET substrate at 500 rpm for 30 s. The spin-coated PDMS was cured at 120 ℃ for 12 h. Then, the cured PDMS was peeled off from the PET substrate and used as a stretchable substrate.\u003c/p\u003e \u003cp\u003eFor mechanical characterization of the \u003cem\u003eis-\u003c/em\u003eEMLs, COS analysis was performed for various solvent treatments. On the cured PDMS substrate, oxygen plasma was applied at 140 W for 90 s, and the \u003cem\u003eis-\u003c/em\u003eHTL was spin-coated at 500 rpm for 60 s and 1000 rpm for 10 s. PDMS with the \u003cem\u003eis-\u003c/em\u003eHTL was annealed on a hot plate at 120 ℃ for 15 min. Then, the sample was transferred to a glove box filled with nitrogen gas. The \u003cem\u003eis-\u003c/em\u003eEML was spin-coated on the \u003cem\u003eis-\u003c/em\u003eHTL at 1500 rpm for 30 s and annealed at 90 ℃ for 10 min. Then, MeOH, IPA, and 2-methoxyethanol were spin-coated on the \u003cem\u003eis-\u003c/em\u003eEML at 4000 rpm for 30 s and annealed at 100 ℃ for 10 min. In the case of the \u003cem\u003eis-\u003c/em\u003eETL, the \u003cem\u003eis-\u003c/em\u003eETL was spin-coated at 5000 rpm for 30 s on the plasma-treated PDMS substrate and annealed on the hot plate at 90 ℃ for 10 min in the glove box. The \u003cem\u003eis-\u003c/em\u003eEMLs and \u003cem\u003eis-\u003c/em\u003eETLs on the PDMS substrate were loaded on a homemade stretching jig. Strain was applied in increments of 10% from 0\u0026ndash;100%.\u003c/p\u003e \u003cdiv id=\"Sec8\" class=\"Section2\"\u003e \u003ch2\u003eFabrication of the ITO anode based rigid OLEDs\u003c/h2\u003e \u003cp\u003eThe slide glass substrate (Paul Marienfeld GmbH \u0026amp; Co. KG, Germany) was cut to 2.5 cm \u0026times; 2.5 cm and sequentially washed in the sonication baths of acetone, IPA, and deionized water for 5 min each. On precleaned glass, ITO (150 nm thick) was deposited using direct current (DC) magnetron sputtering and annealed at 300 ℃ for 30 min inside a glove box filled with nitrogen gas. On the ITO-coated glass, oxygen plasma was applied at 140 W for 90 s. On the plasma-treated ITO glass, an \u003cem\u003eis-\u003c/em\u003eHTL solution was spin-coated at 2000 rpm for 60 s after being filtered through a 1 \u0026micro;m polytetrafluoroethylene (PTFE) syringe filter and annealed at 120 ℃ for 20 min. The sample was then transferred into a glove box filled with nitrogen gas. On the \u003cem\u003eis-\u003c/em\u003eHTL, the \u003cem\u003eis-\u003c/em\u003eEML was spin-coated at 1500 rpm for 30 s and annealed at 100 ℃ for 10 min. Then, the PFN-Br, PEIE, and TX-blended solution was spin-coated on the \u003cem\u003eis-\u003c/em\u003eEML at 5000 rpm for 30 s and annealed at 100 ℃ for 10 min. Finally, the Al cathode was thermally evaporated on the \u003cem\u003eis-\u003c/em\u003eETL with a 150 nm thickness.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec9\" class=\"Section2\"\u003e \u003ch2\u003eFabrication of electron only device\u003c/h2\u003e \u003cp\u003eFor electron only device fabrication, 150 nm Ag anode was deposited on the pre-cleaned glass substrate using thermal evaporator. On the Ag anode, 0.5 wt% d-PEIE solution was spin coated at 5000 rpm for 30 s and annealed at 100 ℃ for 10 min. It was then transferred into a glove box filled with nitrogen gas. On the d-PEIE, \u003cem\u003eis-\u003c/em\u003eEML was spin-coated at 1500 rpm for 30 s and annealed at 100 ℃ for 10 min. Then, PFN-Br, PFNBr:PEIE, PFNBr:PEIE:TX blend solution was spin-coated on the \u003cem\u003eis-\u003c/em\u003eEML at 5000 rpm for 30 s and annealed at 100 ℃ for 10 min. Finally, Al cathode was thermally evaporated on the \u003cem\u003eis-\u003c/em\u003eETL with 150 nm thickness.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec10\" class=\"Section2\"\u003e \u003ch2\u003ePreparation of FOTS on Glass substrate\u003c/h2\u003e \u003cp\u003eA precleaned glass substrate was first treated by O2 plasma at 140 W for 90 s. Then, the glass substrate was vapor annealed in a desiccator with trichloro(1H,1H,2H,2H-perfluorooctyl)silane (FOTS, Sigma‒Aldrich) solution for 30 min and annealed at 150 ℃ for 30 min.\u003c/p\u003e \u003cp\u003e \u003cb\u003eFabrication of\u003c/b\u003e \u003cb\u003eis-\u003c/b\u003e\u003cb\u003eOLEDs\u003c/b\u003e\u003c/p\u003e \u003cp\u003eFor the \u003cem\u003eis-\u003c/em\u003eanode, 0.5 ml of a AgNW (with a diameter of 30 nm and a length of 30 \u0026micro;m; Novarials) solution (1 mg ml\u003csup\u003e-1\u003c/sup\u003e concentration) was spray-coated on the FOTS-treated glass substrate using a patterned metal mask. On the AgNWs, an aerogel solution with 4 wt% ethanol was spin-coated at 1000 rpm for 30 s and annealed at 100\u0026deg;C for 10 min. Then, a PDMS solution in tetrahydrofuran (THF) solvent (base and agent ratio of 10:1 at 20 mg ml\u003csup\u003e-1\u003c/sup\u003e) was spin-coated on the aerogel surface at 1000 rpm for 30 s. Additionally, PDMS (base and agent ratio of 10:1) was spin-coated at 300 rpm for 30 s and cured at 120\u0026deg;C for 12 hours. After the curing process, the AgNW-embedded PDMS was released from the glass substrate.\u003c/p\u003e \u003cp\u003eThe released AgNW-embedded PDMS substrate was reattached to a glass substrate with the AgNW electrode facing up. Before coating with the \u003cem\u003eis-\u003c/em\u003eHTL, oxygen plasma was applied at 140 W for 90 s. Then, an \u003cem\u003eis-\u003c/em\u003eHTL solution was spin-coated at 500 rpm for 60 s and 1000 rpm for 10 s after being filtered through a 1 \u0026micro;m PTFE syringe filter and annealed at 120 ℃ for 15 min. The \u003cem\u003eis-\u003c/em\u003eHTL-coated sample was transferred to a N\u003csub\u003e2\u003c/sub\u003e-filled glove box. In the glove box, the \u003cem\u003eis-\u003c/em\u003eEML was spin-coated at 1500 rpm for 30 s and annealed at 90\u0026deg;C for 5 min. On the \u003cem\u003eis-\u003c/em\u003eEML, \u003cem\u003eis-\u003c/em\u003eETLs was sequentially coated. An \u003cem\u003eis-\u003c/em\u003eETL solution (PFN-Br:PEIE:TX) was spin-coated at 5000 rpm for 30 s and annealed at 90\u0026deg;C for 5 min. Then, a Ag cathode was evaporated on the \u003cem\u003eis-\u003c/em\u003eETL at 1 \u0026Aring; s\u003csup\u003e-1\u003c/sup\u003e up to 60 nm thickness. After the evaporation process, 4 wt% d-PEIE solution was spin-coated on the Ag surface at 1000 rpm for 30 s and annealed at 90\u0026deg;C for 5 min. Finally, the \u003cem\u003eis-\u003c/em\u003eOLED was released from the glass substrate. The 3x2 array device fabrication process was almost the same as the \u003cem\u003eis-\u003c/em\u003eOLED fabrication process. Only the anode and cathode patterns and glass size were different from those for the \u003cem\u003eis-\u003c/em\u003eOLEDs.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec11\" class=\"Section2\"\u003e \u003ch2\u003eOther characterization methods\u003c/h2\u003e \u003cp\u003eThe surface morphology of each film was characterized using AFM (NX-10, Park Systems) and field-emission scanning electron microscopy (FE-SEM, IT-500HR, JEOL). The PL spectra of the devices were measured using a spectrofluorometer (FP- 8550, JASCO Co.). The microstructures were characterized by TEM (JEM-ARM200F \u0026ldquo;NEO ARM,\u0026rdquo; JEOL) and energy-dispersive X-ray spectrometry (EDS, JED-2300T (Dual), JEOL). The luminance\u0026ndash;voltage\u0026ndash;current density (\u003cem\u003eL\u003c/em\u003e\u0026ndash;\u003cem\u003eV\u003c/em\u003e\u0026ndash;\u003cem\u003eJ\u003c/em\u003e) characteristics and EL spectra were measured using a 2400 Keithley Sourcemeter and a CS-200 (CS-2000) Konica-Minolta Chromameter. The optical transmittance of the devices was measured using an ultraviolet\u0026ndash;visible (UV\u0026ndash;VIS) spectrophotometer (V-650, JASCO Co.).\u003c/p\u003e \u003c/div\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eACKNOWLEDGEMENTS\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis work was supported by a National Research Foundation of Korea (NRF) Grant funded by the Korea Government (MSIT) (RS-2023-00302611) and the Technology Innovation Program Development Program (\"20022479\", \"Development of deuterium oxide localization and deuterium benzene synthesis technology to improve OLED lifetime by 25%\") funded by the Ministry of Trade, Industry \u0026amp; Energy (MOTIE, Korea).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAUTHOR CONTRIBUTIONS\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eJ.-H. O., K.-H. J., and J.-W. P. designed the project. J.-H. O. and K.-H. J. carried out the experiments and analysis. J.-H. O., K.-H. J., and J.-W. P.\u0026nbsp;wrote the paper.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCOMPETING INTERESTS\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors declare no competing financial interests.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n \u003cli\u003eKoo, J. H.\u003cem\u003e\u0026nbsp;et al.\u003c/em\u003e Flexible and Stretchable Smart Display: Materials, Fabrication, Device Design, and System Integration. \u003cem\u003eAdv. Funct. Mater.\u003c/em\u003e \u003cstrong\u003e28\u003c/strong\u003e, 1801834 (2018).\u003c/li\u003e\n \u003cli\u003eChen, H. W.\u003cem\u003e\u0026nbsp;et al.\u003c/em\u003e Liquid crystal display and organic light-emitting diode display: present status and future perspectives. \u003cem\u003eLight. Sci. Appl.\u003c/em\u003e \u003cstrong\u003e7\u003c/strong\u003e, 17168 (2018).\u003c/li\u003e\n \u003cli\u003eWang, S. M.\u003cem\u003e\u0026nbsp;et al.\u003c/em\u003e Towards high-power-efficiency solution-processed OLEDs: Material and device perspectives. \u003cem\u003eMater. Sci. Eng. R. Rep.\u003c/em\u003e \u003cstrong\u003e140\u003c/strong\u003e, 100547 (2020).\u003c/li\u003e\n \u003cli\u003eSomeya, T., Bao, Z. N. \u0026amp; Malliaras, G. G. The rise of plastic bioelectronics. \u003cem\u003eNature\u003c/em\u003e \u003cstrong\u003e540\u003c/strong\u003e, 379-385 (2016).\u003c/li\u003e\n \u003cli\u003eSekitani, T.\u003cem\u003e\u0026nbsp;et al.\u003c/em\u003e Stretchable active-matrix organic light-emitting diode display using printable elastic conductors. \u003cem\u003eNature Materials\u003c/em\u003e \u003cstrong\u003e8\u003c/strong\u003e, 494-499 (2009).\u003c/li\u003e\n \u003cli\u003eSingh, M., Haverinen, H. M., Dhagat, P. \u0026amp; Jabbour, G. E. Inkjet printing-process and its applications. \u003cem\u003eAdv. Mater.\u003c/em\u003e \u003cstrong\u003e22\u003c/strong\u003e, 673-685 (2010).\u003c/li\u003e\n \u003cli\u003eYook, K. S. \u0026amp; Lee, J. Y. Small molecule host materials for solution processed phosphorescent organic light-emitting diodes. \u003cem\u003eAdv. Mater.\u003c/em\u003e \u003cstrong\u003e26\u003c/strong\u003e, 4218-4233 (2014).\u003c/li\u003e\n \u003cli\u003eChiba, T., Pu, Y. J. \u0026amp; Kido, J. Solution-processable electron injection materials for organic light-emitting devices. \u003cem\u003eJ. Mater. Chem. C\u003c/em\u003e \u003cstrong\u003e3\u003c/strong\u003e, 11567-11576 (2015).\u003c/li\u003e\n \u003cli\u003eLiang, J. J.\u003cem\u003e\u0026nbsp;et al.\u003c/em\u003e Elastomeric polymer light-emitting devices and displays. \u003cem\u003eNat. Photonics\u003c/em\u003e \u003cstrong\u003e7\u003c/strong\u003e, 817-824 (2013).\u003c/li\u003e\n \u003cli\u003eGao, H., Chen, S., Liang, J. \u0026amp; Pei, Q. Elastomeric Light Emitting Polymer Enhanced by Interpenetrating Networks. \u003cem\u003eACS Appl. Mater. Inter.\u003c/em\u003e \u003cstrong\u003e8\u003c/strong\u003e, 32504-32511 (2016).\u003c/li\u003e\n \u003cli\u003eYin, H.\u003cem\u003e\u0026nbsp;et al.\u003c/em\u003e Structures and Materials in Stretchable Electroluminescent Devices. \u003cem\u003eAdv. Mater.\u003c/em\u003e, e2106184 (2021).\u003c/li\u003e\n \u003cli\u003eZhang, Z.\u003cem\u003e\u0026nbsp;et al.\u003c/em\u003e High-brightness all-polymer stretchable LED with charge-trapping dilution. \u003cem\u003eNature\u003c/em\u003e \u003cstrong\u003e603\u003c/strong\u003e, 624-630 (2022).\u003c/li\u003e\n \u003cli\u003eZhou, H.\u003cem\u003e\u0026nbsp;et al.\u003c/em\u003e Graphene-Based Intrinsically Stretchable 2D-Contact Electrodes for Highly Efficient Organic Light-Emitting Diodes. \u003cem\u003eAdv. Mater.\u003c/em\u003e \u003cstrong\u003e34\u003c/strong\u003e, e2203040 (2022).\u003c/li\u003e\n \u003cli\u003eLiu, Y.\u003cem\u003e\u0026nbsp;et al.\u003c/em\u003e A Self-Assembled 3D Penetrating Nanonetwork for High-Performance Intrinsically Stretchable Polymer Light-Emitting Diodes. \u003cem\u003eAdv. Mater.\u003c/em\u003e \u003cstrong\u003e34\u003c/strong\u003e, e2201844 (2022).\u003c/li\u003e\n \u003cli\u003eLiu, W.\u003cem\u003e\u0026nbsp;et al.\u003c/em\u003e High-efficiency stretchable light-emitting polymers from thermally activated delayed fluorescence. \u003cem\u003eNat. Mater.\u003c/em\u003e \u003cstrong\u003e22\u003c/strong\u003e, 737-745 (2023).\u003c/li\u003e\n \u003cli\u003eKim, J. H. \u0026amp; Park, J. W. Intrinsically stretchable organic light-emitting diodes. \u003cem\u003eSci. Adv.\u003c/em\u003e \u003cstrong\u003e7\u003c/strong\u003e, eabd9715 (2021).\u003c/li\u003e\n \u003cli\u003eOh, J. H. \u0026amp; Park, J. W. Intrinsically Stretchable Phosphorescent Light-Emitting Materials for Stretchable Displays. \u003cem\u003eACS Appl. Mater. Inter.\u003c/em\u003e \u003cstrong\u003e15\u003c/strong\u003e, 33784-33796 (2023).\u003c/li\u003e\n \u003cli\u003eJeon, K. H. \u0026amp; Park, J. W. Light-Emitting Polymer Blended with Elastomers for Stretchable Polymer Light-Emitting Diodes. \u003cem\u003eMacromolecules\u003c/em\u003e \u003cstrong\u003e5\u003c/strong\u003e, 8311-8320 (2022).\u003c/li\u003e\n \u003cli\u003eZhou, H.\u003cem\u003e\u0026nbsp;et al.\u003c/em\u003e Intrinsically stretchable low-dimensional conductors for wearable organic light-emitting diodes. \u003cem\u003eDevice\u003c/em\u003e \u003cstrong\u003e1\u003c/strong\u003e, 100060 (2023).\u003c/li\u003e\n \u003cli\u003eHan, S. J.\u003cem\u003e\u0026nbsp;et al.\u003c/em\u003e Achieving Low‐Voltage Operation of Intrinsically‐Stretchable Organic Light‐Emitting Diodes. \u003cem\u003eAdv. Funct. Mater.\u003c/em\u003e \u003cstrong\u003e33\u003c/strong\u003e, 2211150 (2023).\u003c/li\u003e\n \u003cli\u003eWu, W. Stretchable electronics: functional materials, fabrication strategies and applications. \u003cem\u003eSci. Technol. Adv. Mater.\u003c/em\u003e \u003cstrong\u003e20\u003c/strong\u003e, 187-224 (2019).\u003c/li\u003e\n \u003cli\u003eLee, H.\u003cem\u003e\u0026nbsp;et al.\u003c/em\u003e Stretchable organic optoelectronic devices: Design of materials, structures, and applications. \u003cem\u003eMater. Sci. Eng. R. Rep.\u003c/em\u003e \u003cstrong\u003e146\u003c/strong\u003e, 100631 (2021).\u003c/li\u003e\n \u003cli\u003eKang, H.\u003cem\u003e\u0026nbsp;et al.\u003c/em\u003e Polymer-metal hybrid transparent electrodes for flexible electronics. \u003cem\u003eNat. Commun.\u003c/em\u003e \u003cstrong\u003e6\u003c/strong\u003e, 6503 (2015).\u003c/li\u003e\n \u003cli\u003eBi, Y. G.\u003cem\u003e\u0026nbsp;et al.\u003c/em\u003e Ultrathin Metal Films as the Transparent Electrode in ITO‐Free Organic Optoelectronic Devices. \u003cem\u003eAdv. Opt. Mater.\u003c/em\u003e \u003cstrong\u003e7\u003c/strong\u003e, 1800778 (2019).\u003c/li\u003e\n \u003cli\u003ePark, S. I.\u003cem\u003e\u0026nbsp;et al.\u003c/em\u003e Theoretical and Experimental Studies of Bending of Inorganic Electronic Materials on Plastic Substrates. \u003cem\u003eAdv. Funct. Mater.\u003c/em\u003e \u003cstrong\u003e18\u003c/strong\u003e, 2673-2684 (2008).\u003c/li\u003e\n \u003cli\u003eOhisa, S.\u003cem\u003e\u0026nbsp;et al.\u003c/em\u003e Conjugated Polyelectrolyte Blend with Polyethyleneimine Ethoxylated for Thickness-Insensitive Electron Injection Layers in Organic Light-Emitting Devices. \u003cem\u003eACS Appl. Mater. Inter.\u003c/em\u003e \u003cstrong\u003e10\u003c/strong\u003e, 17318-17326 (2018).\u003c/li\u003e\n \u003cli\u003eJiang, Z.\u003cem\u003e\u0026nbsp;et al.\u003c/em\u003e A 1.3-micrometre-thick elastic conductor for seamless on-skin and implantable sensors. \u003cem\u003eNat. Electron.\u003c/em\u003e \u003cstrong\u003e5\u003c/strong\u003e, 784-793 (2022).\u003c/li\u003e\n \u003cli\u003eZhu, T.\u003cem\u003e\u0026nbsp;et al.\u003c/em\u003e Highly stable and strain-insensitive metal film conductors via manipulating strain distribution. \u003cem\u003eMater. Horiz.\u003c/em\u003e \u003cstrong\u003e10\u003c/strong\u003e, 5920-5930 (2023).\u003c/li\u003e\n \u003cli\u003eHan, S.\u003cem\u003e\u0026nbsp;et al.\u003c/em\u003e Enhanced stretchability of metal/interlayer/metal hybrid electrode. \u003cem\u003eNanoscale\u003c/em\u003e \u003cstrong\u003e13\u003c/strong\u003e, 4543-4550 (2021).\u003c/li\u003e\n \u003cli\u003eKim, S. W.\u003cem\u003e\u0026nbsp;et al.\u003c/em\u003e Omnidirectionally Stretchable Metal Films with Preformed Radial Nanocracks for Soft Electronics. \u003cem\u003eACS Appl. Nano. Mater.\u003c/em\u003e \u003cstrong\u003e3\u003c/strong\u003e, 7192-7200 (2020).\u003c/li\u003e\n \u003cli\u003eWon, D.\u003cem\u003e\u0026nbsp;et al.\u003c/em\u003e Transparent Electronics for Wearable Electronics Application. \u003cem\u003eChem. Rev.\u003c/em\u003e \u003cstrong\u003e123\u003c/strong\u003e, 9982-10078 (2023).\u003c/li\u003e\n \u003cli\u003eKim, M. H.\u003cem\u003e\u0026nbsp;et al.\u003c/em\u003e Mechanically robust stretchable semiconductor metallization for skin-inspired organic transistors. \u003cem\u003eSci. Adv.\u003c/em\u003e \u003cstrong\u003e8\u003c/strong\u003e, eade298 (2022).\u003c/li\u003e\n \u003cli\u003eKim, J. H. \u0026amp; Park, J. W. Designing an electron-transport layer for highly efficient, reliable, and solution-processed organic light-emitting diodes. \u003cem\u003eJ. Mater. Chem. C\u003c/em\u003e \u003cstrong\u003e5\u003c/strong\u003e, 3097-3106 (2017).\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"npj-flexible-electronics","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"npjflexelectron","sideBox":"Learn more about [npj Flexible Electronics](http://www.nature.com/npjflexelectron/)","snPcode":"41528","submissionUrl":"https://submission.springernature.com/new-submission/41528/3","title":"npj Flexible Electronics","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"NPJ","inReviewEnabled":true,"inReviewRevisionsEnabled":true},"keywords":"","lastPublishedDoi":"10.21203/rs.3.rs-4215709/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-4215709/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eRecently, the growing desire to conformally integrate electronics with the human body in the form of wearable devices has spurred the need for additional form factors, skin-like softness, and stretchability of organic light-emitting diodes (OLEDs). Traditional intrinsically stretchable OLED (\u003cem\u003eis-\u003c/em\u003eOLED) approaches have focused on improving the luminance and stretchability through methods such as blending materials to endow the component layers with stretchability and complex lamination processes. However, the designed microstructure of the blended layer cannot be maintained due to the different orthogonality between the solvents of subsequently coated layers. In addition, the lamination method often leads to degradation of the performance due to delamination induced by formed defects. To overcome these challenges, we developed a sequentially coated \u003cem\u003eis-\u003c/em\u003eOLED and confirmed the maintenance of the designed morphologies of each layer and a highly stretchable metallic \u003cem\u003eis-\u003c/em\u003ecathode. Our \u003cem\u003eis-\u003c/em\u003eOLEDs achieved a maximum total luminance of 3,151 cd m\u003csup\u003e-2\u003c/sup\u003e and a total current efficiency of 5.4 cd A\u003csup\u003e-1\u003c/sup\u003e (on both the anode and cathode sides). Furthermore, our \u003cem\u003eis-\u003c/em\u003eOLEDs exhibited a higher static stretchability of up to 70% than previous work and a notable cyclic stretchability, maintaining 80% of the luminance at 0% strain after 300 stretching cycles under 40% strain. This breakthrough in the fabrication process, coupled with the use of novel stretchable materials, represents a significant step forward in the field of \u003cem\u003eis-\u003c/em\u003eOLED technology, potentially leading to a new era of highly durable and efficient soft electronic devices.\u003c/p\u003e","manuscriptTitle":"Intrinsically Stretchable OLEDs with a Designed Morphology-Sustainable Layer and Stretchable Metal Cathode","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-04-19 06:05:35","doi":"10.21203/rs.3.rs-4215709/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"revise","date":"2024-05-14T04:52:58+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"This content is not available.","date":"2024-05-13T13:46:03+00:00","index":3,"fulltext":"This content is not available."},{"type":"editorInvitedReview","content":"This content is not available.","date":"2024-04-29T12:51:52+00:00","index":2,"fulltext":"This content is not available."},{"type":"editorInvitedReview","content":"This content is not available.","date":"2024-04-28T12:23:15+00:00","index":1,"fulltext":"This content is not available."},{"type":"reviewerAgreed","content":"This content is not available.","date":"2024-04-16T12:41:49+00:00","index":3,"fulltext":"This content is not available."},{"type":"reviewerAgreed","content":"This content is not available.","date":"2024-04-16T02:23:52+00:00","index":2,"fulltext":"This content is not available."},{"type":"reviewerAgreed","content":"This content is not available.","date":"2024-04-16T02:17:55+00:00","index":1,"fulltext":"This content is not available."},{"type":"reviewersInvited","content":"","date":"2024-04-16T02:12:47+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2024-04-05T09:15:22+00:00","index":"","fulltext":""},{"type":"submitted","content":"npj Flexible Electronics","date":"2024-04-04T05:06:28+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2024-04-04T05:06:28+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"npj-flexible-electronics","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"npjflexelectron","sideBox":"Learn more about [npj Flexible Electronics](http://www.nature.com/npjflexelectron/)","snPcode":"41528","submissionUrl":"https://submission.springernature.com/new-submission/41528/3","title":"npj Flexible Electronics","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"NPJ","inReviewEnabled":true,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"a2b70cee-a09e-48b3-af00-dd7c533bd87b","owner":[],"postedDate":"April 19th, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[{"id":30721147,"name":"Physical sciences/Materials science"},{"id":30721148,"name":"Physical sciences/Optics and photonics"}],"tags":[],"updatedAt":"2024-07-27T07:09:39+00:00","versionOfRecord":{"articleIdentity":"rs-4215709","link":"https://doi.org/10.1038/s41528-024-00332-0","journal":{"identity":"npj-flexible-electronics","isVorOnly":false,"title":"npj Flexible Electronics"},"publishedOn":"2024-07-26 04:00:00","publishedOnDateReadable":"July 26th, 2024"},"versionCreatedAt":"2024-04-19 06:05:35","video":"","vorDoi":"10.1038/s41528-024-00332-0","vorDoiUrl":"https://doi.org/10.1038/s41528-024-00332-0","workflowStages":[]},"version":"v1","identity":"rs-4215709","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-4215709","identity":"rs-4215709","version":["v1"]},"buildId":"qtupq5eGEP_6zYnWcrvyt","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}