Assemblable thermoelectric Lego blocks for reconfigurable, self- healing, and flexible power generators

Assemblable thermoelectric Lego blocks for reconfigurable, self- healing, and flexible power generators | 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 Assemblable thermoelectric Lego blocks for reconfigurable, self- healing, and flexible power generators Keonkuk Kim, Kyuha Park, Jihyang Song, Ji Eun Lee, Donghee Son, and 1 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-8142150/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 20 Jan, 2026 Read the published version in npj Flexible Electronics → Version 1 posted 11 You are reading this latest preprint version Abstract Thermoelectric devices offer a promising route for waste-heat recovery, yet conventional modules—consisting of multiple pairs of inorganic legs soldered to rigid metal electrodes—are intrinsically brittle and nearly impossible to repair or reconfigure once fabricated. Although recent incorporation of flexible or stretchable polymeric components has improved mechanical deformability, these integrated architectures cannot be modified for new functions or restored. In this study, we propose the concept of Lego-like thermoelectric leg blocks that enable on-demand repair and reconfiguration via modular assembly. Each block operates as an independent unit comprising PDMS-based, self-healing Ag-flake-embedded composite electrodes and 3D-printed BiSbTe and BiTeSe thermoelectric legs, yielding flexible, repairable, and modular devices. Assembled devices preserve performance under bending (radius ≈ 3.4 mm), stretching (40%), and even after cutting and reassembly. Moreover, repeated disassembly/reassembly into diverse geometries proceeds without measurable loss in power output. Our Lego-like blocks provide a versatile thermoelectric platform that combines flexibility, reparability, and reconfigurability. Physical sciences/Energy science and technology Physical sciences/Engineering Physical sciences/Materials science Figures Figure 1 Figure 2 Figure 3 Figure 4 Introduction Thermoelectric (TE) devices, which can directly convert heat into electricity or vice versa, have garnered significant attention as a promising technology for waste heat recovery and solid-state cooling 1 – 3 . The fundamental principle relies on the Seebeck and Peltier effects, enabling them to operate as clean and quiet energy converters. Conventional TE devices adopt a planar architecture in which multiple pairs of n-type and p-type TE legs are soldered to top and bottom metal electrodes on ceramic substrates. All components are rigid inorganic layers connected electrically in series and thermally in parallel. This architecture resists conformal contact with non-planar heat sources (e.g., pipes or ducts), incurring parasitic thermal losses 4 – 6 . Moreover, the intrinsic brittleness of the inorganic components renders devices vulnerable to fracture under prolonged vibration or mechanical shock where the failure of a single junction can disable the entire device 7 – 10 . Repair or reconfiguration is technically infeasible, typically requiring full disassembly and reassembly of all components. To address the inherent limitations of conventional bulk TE devices, flexible TE devices have emerged as compelling alternatives 11 – 14 . Their ability to conform to non-planar heat sources markedly improves interfacial heat transfer, while their superior mechanical compliance enhances reliability under external stress, enabling longer operational lifetimes. Additionally, they offer enhanced mechanical reliability under external stresses, ensuring stable performance over a longer operational lifetime. This progress has expanded application areas, particularly in wearable electronics where mechanical flexibility is essential 15 – 19 . More recently, the integration of self-healing functionality—implemented in electrodes and/or TE legs—has been proposed to further improve robustness by autonomously repairing microcracks, scratches, and other localized defects, thereby extending service life and reducing maintenance demands 20 – 23 . Despite these advances, most studies have concentrated on localized damage repair; leveraging self-healing for device-level reconfiguration along with purposeful structural design remains largely underexplored. Here, we propose the concept of Lego-like TE leg blocks that can be assembled into devices with arbitrary architecture. Each block functions as an independent, reconfigurable unit featuring self-healing electrodes, enabling the construction of flexible, repairable, and modular TE generators (TEGs) (Fig. 1 a). To realize this design, we employed a PDMS-based self-healing polymer (SHP) and Ag-flake-dispersed SHP (AgF-SHP) as electrode materials, integrated with 3D-printed (Bi,Sb) 2 Te 3 and Bi 2 (Te,Se) 3 TE legs to form TE Lego blocks (Fig. 1 b). The assembled devices retained their performance under bending, stretching, and even after cutting and reassembly (Figs. 1 c-e), withstanding a bending radius of about 3.4 mm and a stretching strain of up to 40%. Furthermore, the devices could be repeatedly disassembled and reassembled into diverse geometries (U, V, and W shapes) without degradation in power output, demonstrating the reconfiguration capability of the Lego blocks. This concept thus provides TE leg-level assemblability, delivering true architectural freedom and establishing a robust, versatile, and easily repairable platform for next-generation TE technology. Results Fabrication of TE Lego blocks TE Lego blocks were fabricated with the 3D-printed TE legs and self-healing AgF–SHP composite electrodes. The self-healing electrodes were connected to the top and bottom surfaces of TE legs employing conductive Ag adhesive. For TE legs, Bi 0.5 Sb 1.5 Te 3 (BST) and Bi 2 Te 2.7 Se 0.3 (BTS) were chosen as the p-type and n-type TE materials, respectively, as their compositions are known to exhibit high TE properties near room temperature 24 – 26 . We fabricated three different types of TE Lego blocks for the device assembly, depending on the direction of electrodes, 90°, 180°, and 270°, which allows the integration of TE Lego blocks into diverse architectures of devices. We denoted the type of the TE Lego blocks depending on their carrier type of the TE materials and the top and bottom electrode angle; e.g. P-90, N-90, P-180, N-180, P-270, and N-270. These components are then assembled as desired to fabricate the TE Lego blocks. The SHP and AgF-SHP composite films were fabricated by adapting a previously reported procedure 27 . A homogeneous SHP solution was prepared by dissolving pre-synthesized SHP in chloroform (CHCl 3 ), which was then cast and subsequently dried to fabricate the film (Supplementary Fig. 1). The SHP itself was prepared according to the previous literature method 28 . The self-healing efficiency can be enhanced through thermal or plasma treatments (Methods). For the electrode parts of the TE Lego block, an SHP film was cut into a "U" shape. A AgF-SHP film with the rectangular-shaped pattern was then inserted into the center opening of the U-shaped SHP film, resulting in a final square geometry for the electrode assembly. The center part of the block was constructed by stacking multiple layers of hollow-squared cut SHP films, creating an internal cavity designed to house the TE leg. Finally, the complete TE Lego block was assembled by integrating the upper electrode part, the center part containing a 3D-printed TE leg fabricated as described in a later section, and the lower electrode part. For the production of TE leg materials, we used the extrusion-based 3D printing method with the 3D-printable inks of the TE particle colloids with desired rheological properties (Supplementary Fig. 2). We used the modified method of that developed by our group previously 29 – 33 . Briefly, well-dispersed colloidal ink was prepared by vigorously mixing mechanically alloyed BST and BTS particles obtained via ball milling in a glycerol medium. The ball-milled BST and BTS particles exhibited high zeta potential values of -27.6 mV and − 32.8 mV, respectively, indicating a significant surface charge on the synthesized particles. The TE colloidal ink was formulated with a high particle loading of approximately 30 vol% to achieve the high viscoelasticity required for subsequent 3D printing. The suitability of the formulated TE colloidal inks for 3D printing was verified by measuring their viscoelastic properties using a rheometer. Under an angular frequency sweep, the complex viscosity at 0.06 rad·s − 1 was approximately 6.59×10 5 Pa·s for the BST ink and 8.57×10 5 Pa·s for the BTS ink. Furthermore, in a shear stress sweep condition, the storage modulus values prior to the yield point ranged from 1.21–1.41×10 4 Pa for the BST ink and 2.25–2.66×10 4 Pa for the BTS ink. These values are comparable to those of previously reported 3D direct-writable Bi 2 Te 3 -based inks formulated without additives. These inks were 3D-printed to produce several tens of TE legs in a single pass (Supplementary Fig. 3). The subsequent heat treatment at 450 o C generated well-sintered BST and BTS TE legs. Furthermore, the sintered p-type and n-type legs were found to display nearly identical volume shrinkage ratios (Supplementary Fig. 4), which simplifies the fabrication of dimensionally controlled TE Lego blocks. Material properties of the TE leg block components To utilize the self-healing AgF-SHP composites as TE power generation that requires the operation at high temperatures, we investigated various properties of these composites at elevated temperatures. First, the rheological behavior of AgF–SHP composites by monitoring their shear stress responses at 25, 50, 75, and 100°C under oscillatory frequencies ranging from 0.01 to 100 Hz (Figs. 2 a-e). The thermal properties of AgF–SHP composites with varying Ag flake loadings consistently exhibited high storage and loss modulus values, suggesting superior thermal resistance compared to conventional amorphous polymers attributed to the strong hydrogen bonding interactions within the polyurea framework. Notably, the sample with SHP: AgF of 1:4 in the weight ratio, employed as the electrode, maintained stable behavior in the range of 25–50°C indicating the preservation of viscoelastic balance, while regions with tangent δ (tan δ = G'' / G' ) values exceeding 1 emerged at temperatures above 75°C, signifying a transition toward a more viscous-dominated response. In addition, although increasing the amount of AgFs makes the AgF-SHP composite stiffer, we found that variations in AgF weight loading ratios (1:1, 1:2, and 1:3) exerted only a negligible influence on the tan δ (Supplementary Fig. 5). This indicates that the damping characteristics of the composites were largely preserved regardless of filler content, suggesting that the incorporation between Ag-flakes and SHP does not substantially perturb the intrinsic rheological characteristics of SHP. Differential scanning calorimetry (DSC) was also conducted in the temperature range of − 80 to 80°C for AgF–SHP composites with SHP:AgF weight ratios of 1:1, 1:2, 1:3, and 1:4 (Supplementary Fig. 6). All the composites exhibited only minimal thermal transitions below 0°C, confirming the amorphous behavior of the AgF–SHP backbone. Furthermore, the variation in heat flow progressively decreased when the Ag-flakes content increased. Since DSC quantifies the amount of heat absorption or released during temperature fluctuations, these results indicate a reduction in absolute heat flow variation with increasing Ag-flakes ratio. Importantly, no evidence of oxidation–reduction processes between Ag-flakes and SHP was detected within the investigated temperature range, and no structural changes in either component were observed below 80°C. These findings are in agreement with previously reported results for similar polymer-filler systems 34 . Thermogravimetric analysis (TGA) further verified the excellent thermal stability of the AgF-SHP where no significant weight loss or thermal degradation was observed up to 220°C (Supplementary Fig. 7). Collectively, the combined DSC and TGA results confirm that the AgF-SHP composite preserves a stable structure under repeated thermal cycling between 25 and 75°C. These attributes underscore its potential utility in TEG platforms at elevated temperatures. We investigated the temperature-dependent electrical conductivity ( σ ) of the as-synthesized AgF-SHP composite samples within the typical operating temperature range of TEGs, from 20°C to 70°C (Fig. 2 f). The measurement results showed that the electrical conductivity of the AgF-SHP composite reached a maximum value of approximately 141 S cm − 1 at room temperature. As the temperature increased, the electrical conductivity decreased, reaching approximately 101 S cm − 1 at 70°C. This behavior is presumably attributed to the metallic property of the AgFs, which are the primary conductive component of the composite. Furthermore, the thermal conductivities ( κ ) measurement was conducted for both the pristine SHP and the AgF-SHP composite samples (Figs. 2 g and 2 h). For the pristine SHP sample, which contains no dispersed silver flakes, the thermal conductivity showed a maximum value of approximately 0.14 W m − 1 K − 1 at room temperature, decreasing to approximately 0.11 W m − 1 K − 1 at 70°C. This trend of decreasing thermal conductivity with increasing temperature is consistent with the reported intrinsic material properties of polydimethylsiloxane (PDMS) 35 , 36 , which is the main component of the SHP. In the case of the AgF-SHP composite sample, it shows the maximum thermal conductivity value of about 1.10 W m − 1 K − 1 at room temperature, which similarly decreased as the temperature increases, reaching a value of about 0.98 W m − 1 K − 1 at 70°C. This appears to be a phenomenon attributed to the metallic properties of the silver flakes, as observed previously. Notably, the thermal conductivity of the AgF-SHP composite sample was approximately one order of magnitude higher than that of the pristine SHP. This significant increase is ascribed to the extremely high thermal conductivity of the dispersed silver particles within the composite sample 37 . We also characterized the temperature-dependent electrical and thermal properties of the 3D-printed BST and BTS samples. Specifically, the electrical conductivities at room temperature for p-type BST and n-type BTS were about 4,240 S cm − 1 and 12,500 S cm − 1 , respectively (Fig. 2 i). Both samples exhibited the characteristic behavior of degenerate semiconductors, with the electrical conductivity gradually decreasing as the temperature increased. Regarding the Seebeck coefficient, the p-type BST sample showed a value of approximately 221.5 µV K − 1 at room temperature, which gradually increased to a peak value of approximately 242.7 µV K⁻¹ at around 100°C, while the n-type BTS sample showed a tendency for its absolute value to increase with temperature within the range of -110.3 to -147.0 µV K − 1 (Fig. 2 j). Consequently, the resulting maximum power factor values for the BST and BTS materials were 2.08 and 1.58 mW m − 1 K − 2 , respectively (Supplementary Fig. 8). The thermal conductivity of the BST sample increased with temperature, ranging from 0.62 to 0.96 W m − 1 K − 1 , whereas the thermal conductivity of the BTS sample showed weak temperature dependence, remaining between 1.00 and 1.08 W m − 1 K − 1 (Fig. 2 k). These values are comparatively lower than those of their bulk samples, which is attributed to the inherent high porosity of samples (26% for BST and 21% for BTS) fabricated through the 3D printing process. Finally, the figure of merit ( ZT ) values of the TE samples were calculated from the measured electrical and thermal properties (Fig. 2 l). The p-type BST achieved a ZT of 1.02 at room temperature and a peak ZT of 1.07 at approximately 50°C. The n-type BTS exhibited a ZT of 0.43 at room temperature, reaching a maximum value of approximately 0.65 at around 175°C. These values are comparable to those of the previously reported 3D-printed materials with corresponding compositions 24 – 26 . Mechanical deformation and self-healing properties of the TE Lego block The mechanical deformation properties of the assembled TE device made of the TE Lego blocks were initially characterized using a uniaxial stretcher to perform bending and stretching tests at room temperature. During the bending test, which was performed by progressively decreasing the stretcher's gap, the electrical resistance of the device was slightly decreased as the bending radius decreased (Fig. 3 a). Specifically, the electrical resistance continuously dropped until a minimum bending radius of approximately 3.4 mm was reached, at which point the resistance was about 17% lower than that of the original flat device. As previously reported, this reduction is attributed to the electrical self-boosting effect in the AgF-SHP, which enhances its electrical conductivity 27 . This is considered the primary cause for the observed reduction in total device resistance. In the stretching test, performed by increasing the stretcher's gap, the device's electrical resistance first decreased up to about 10% strain (Fig. 3 b). This behavior is likely attributed to the self-boosting effect in the AgF-SHP sample at low strains up to about 10%, as previously observed. With further elongation, the electrical resistance began to increase and returned to its original value at about 30% strain. Beyond this point, a sharp rise in electrical resistance occurred. However, upon further stretching, the mechanical adhesion between the AgF-SHP sample and the 3D-printed TE leg appears to weaken. This would increase the contact resistance, leading to the observed rise in the device's total electrical resistance. Thus, it was confirmed that even under mechanical deformation conditions of bending and stretching, there was no significant difference in the performance of the TE device assembled from TE Lego blocks. We also investigated the self-healing capability of the AgF-SHP electrode (Fig. 3 c), as this property is a key factor enabling the “Lego-like” behavior of the TE Lego block devices. Initially, we assembled a 2×2 array TE device by properly arranging four TE Lego blocks in an electrically continuous connection. Upon their disassembly into individual blocks, the electrical connection was interrupted. However, after subsequent reassembly, the AgF-SHP electrodes underwent self-healing, and the final TE device successfully re-established their electrical connectivity. To quantitatively investigate the self-healing behavior of the AgF-SHP electrode within the TE Lego block, we monitored the evolution of electrical resistance following two types of damage, surface scratching and complete cutting. When the electrode was scratched, its resistance immediately increased by approximately 45% yet exhibited a rapid recovery (Fig. 3 d). Remarkably, the electrical resistance returned to within 2% of its original value within 200 sec, without external stimuli applied to facilitate the healing process. In the case of cutting, the complete detachment of the assembled TE device to individual TE Lego blocks, a total loss of electrical connectivity was observed (Fig. 3 e). Upon re-establishing contact between the severed AgF-SHP interfaces in their proper orientation, an immediate self-healing process restored the electrical conductivity of the device. Furthermore, the application of gentle pressure after reassembly not only accelerated the self-healing speed but also enabled the electrical performance to recover to a level nearly identical to its original state. Capitalizing on these self-healing capabilities, we compared the power generation performance of an original TE device composed of two pairs of p-type and n-type TE Lego blocks with that of a self-healed device after cutting (Fig. 3 f). At a temperature difference ( ∆T ) of 50°C, the original device exhibited an open-circuit voltage ( V oc ) of approximately 15.4 mV and an output power of approximately 10.94 µW. After the self-healing process, the re-assembled device demonstrated a V oc of approximately 15.3 mV and the output power of approximately 10.36 µW under the same ∆T. These results represent performance deviations of only 0.7% and 5.6%, respectively, from the original values. This high degree of performance recovery demonstrates that it is possible to assemble and reconfigure these TE Lego blocks into new TE devices. Lego-like device assembly and reconfiguration of TEG A key characteristic of conventional Lego blocks is their ability to not only be assembled, but also to be disassembled and reconfigured into new structures. To evaluate if our newly proposed TE Lego blocks show these "Lego-like" characteristics, we first fabricated individual blocks and then constructed TE devices using them in various combinations. Prior to TE device fabrication, a total of twelve TE Lego blocks was prepared, consisting of two blocks each of six different types: P-90, P-180, P-270, N-90, N-180, and N-270 (Fig. 4 a). These blocks were then used for the assembly and reconfiguration into TE devices for the power generation. Unlike conventional TE devices which generally use Cu electrodes with extremely high thermal conductivity, the TE Lego block devices use AgF-SHP samples with very low thermal conductivity. Consequently, the actual ∆T created across the TE legs when subjected to high and low temperatures on either side of the device could be smaller than that observed in that of a conventional device (Supplementary Fig. 9). Therefore, to ensure sufficient ∆T and enhance output power, we prepared the TE legs with a relatively high aspect ratio of 1.5 for the power generation application. The assembly test of the TE Lego block array was first conducted (Fig. 4 b). We progressively assembled 2-pairs (4×1 array), 4-pairs (4×2 array), and 6-pair (4×3 array) TE devices, starting from an initial 2-pair device, while ensuring the electrical connectivity of the entire device was maintained. Subsequently, a temperature difference was applied across both sides of each device configuration, and the output voltage and output power were measured. During the power-generation test, the hot side was heated using a ceramic plate whose temperature could be controlled by the applied current, while the cold side was cooled with a Cu block maintained at 20°C by a cooling chiller. Measurements of hot- and cold-side temperatures, output voltage, and device resistance were carried out under equivalent ∆T conditions (Figs. 4 c–e). As the hot-side temperature increased, the ∆T across the devices increased correspondingly. In each pair device, the output voltage exhibited a linear dependence with increasing ∆T , and the output voltage increased proportionally with the number of pairs in the device under the same ∆T . Moreover, the quadratic dependence of output power further supported the reliability of the measurements. Consequently, a maximum output voltage of 42.2 mV and an output power of 28.7 µW were achieved at the maximum temperature difference of 50°C in the 4×3 array 6-pairs device. These measured results were also confirmed to be consistent with the output voltage of simulation results under the same environmental conditions (Supplementary Fig. 10). The reconfiguration capability was also demonstrated using the same set of TE Lego blocks. Unlike conventional TEGs which are rigid cuboid arrays, the TE Lego block generator allows for a high degree of freedom in device architecture, as long as electrical series connectivity is maintained. Specifically, the twelve p-type and n-type TE Lego blocks was assembled into a U-shaped TE device. The blocks were then disassembled and reassembled to reconfigure the device into V- and W-shaped architectures (Fig. 4 f). These configurations maintain electrical serial connection as the p-type and n-type legs are connected alternately. Furthermore, if a change in device design or dimension is required, reconfiguration is easily accomplished by disassembly of the individual TE Lego blocks and forming new structures (Supplementary Fig. 11). The TE power generation performance of the U-, V- and W-shaped TE Lego block generators were measured by applying a ∆T across both sides using the same method as before (Figs. 4 g–i). At a ∆T of approximately 50°C, all three devices exhibited V oc values ranging from 42.5 to 46.5 mV, confirming no significant difference in their device performance (Supplementary Fig. 12). The output power ranged from 26.38 µW to 32.78 µW under the same ∆T. While this may seem like a relatively large variation, considering that the output power is proportional to the square of the voltage, it indicates that the difference in the total electrical resistance of the device was minimal. These results demonstrate that the use of TE Lego blocks for TE device construction provides broad structural flexibility without significant performance degradation. Discussion We have demonstrated modular, “Lego-like” TE blocks that enable on-demand assembly, repair, and reconfiguration while providing mechanical flexibility and electrical self-healing. Each block combines 3D-printed TE legs with conductive, self-healing AgF-SHP electrodes. The self-healing capability—validated by scratch and detachment tests—reliably restores electrical connection after disassembly and reassembly, underpinning robust reconfigurability. Assembled devices maintain stable performance under substantial bending and tensile strain, and reconfiguration into diverse architectures (e.g., U-, V-, and W-shapes) proceeds without significant loss of power output. Collectively, this freely reconfigurable and repairable approach overcomes limitations of conventional rigid TEGs and paves the way for customizable, durable, and structurally adaptable TE energy-harvesting systems. Methods Materials 4,4′-Methylenebis(phenyl isocyanate) (MDI) and isophorone diisocyanate (IPDI) were sourced from TCI Chemicals. Ag-flakes (AgFs, DSF500MWZ-S) were supplied from Daejoo Electronics. Bis(3-aminopropyl)-terminated poly(dimethylsiloxane) (H 2 N-PDMS-NH 2 , M n = 5000–7000) was a product of Gelest. Bismuth (Bi), Antimony (Sb), Tellurium (Te), and Selenium (Se) granules (all 99.999% purity) were purchased from Thermoelectric Total Solution. All other chemicals and solvents, including octadecyltrichlorosilane (OTS), octadecyltrimethoxysilane (OTMS), and glycerol (> 99.5%), were purchased from Sigma-Aldrich. All the reagents were used as received without further purification. Fabrication of SHP and AgF–SHP Composite Thin Films Before fabricating SHP films, SHP was synthesized via a urea coupling reaction following previously reported protocol 28 . In a typical procedure, Et 3 N (10 mL) was added to a solution of H 2 N-PDMS-NH 2 (100 g) in CHCl 3 (400 mL) under an argon atmosphere at 0°C. After 1 h of stirring, a solution of MDI (2.0 g) and IPDI (2.7 g) in CHCl 3 (10 mL) was introduced dropwise. The reaction mixture was stirred for an additional 1 h at 0°C, gradually warmed to room temperature, and allowed to proceed for 4 days. Excess isocyanates were quenched by the addition of MeOH (15 mL), followed by 30 min of stirring. The crude product was concentrated, precipitated in MeOH (60 mL), filtered, and thoroughly washed with CHCl 3 . Silicon dioxide wafer (SiO 2 ) was functionalized with OTS as previously described 27 . The slides were sequentially cleaned with acetone and isopropyl alcohol, followed by oxygen plasma treatment (100 W, 200 mTorr, 2 min; Scientific Engineering, Korea). Substrates were immersed in a 0.5% (v/v) OTS/n-hexane solution for 1 h, rinsed with ethanol, and dried under nitrogen. Annealing was carried out on a hot plate at 120°C for 30 min, followed by sonication in CHCl 3 for 5 min to remove unbound silane residues. The SHP and AgF–SHP composite films were fabricated following a modified version of our previously reported protocol. 4 Synthesized SHP was dissolved in CHCl 3 (2 g/10 mL) and stirred for 1 h to obtain a homogeneous solution. AgFs were then added at different weight ratios (1:1 to 1:4, corresponding to 2–8 g of AgFs), followed by 30 min of stirring. The mixture was cast onto OTMS-treated SiO 2 wafers and dried at room temperature for 1 h. After drying, the resulting SHP and AgF-SHP thin films were easily detached from the OTMS-functionalized SiO 2 wafer substrate. Film thicknesses were measured using a surface profiler (Dektak 150, Bruker). SHP-surface treatment based on photolithography was carried out using a mask aligner (MA6 Gen4, SUSS MicroTec SE, NFEC-2025-08-307674, Germany), operated at the i-line (365 nm). Wedge-error compensation (WEC) was optimised prior to exposure, and vacuum contact at was employed to minimise mask–substrate tilt. A target exposure dose of 322 mJ cm − 2 was used. Fabrication of 3D-printed TE legs The p-type BST and n-type BTS TE particles with compositions of Bi 0.5 Sb 1.5 Te 3 and Bi 2 Te 2.8 Se 0.3 , respectively, were synthesized by mechanical alloying using a planetary ball mill (Planetary Mono Mill, PULVERISETTE 6) operated at 450 rpm for 11 hours. The ball milling process was performed in a zirconia jar with 5 mm zirconia balls at a 5:1 ball-to-powder weight ratio. The resulting powders were then sieved through a 45 µm mesh to obtain fine particles with a controlled size distribution. The p-type and n-type TE inks were prepared by mixing 9.2 g of ball-milled BST particles and 10.8 g of ball-milled BTS particles, respectively, with 4 g of glycerol using a planetary centrifugal mixer (ARM-100, Thinky). The mixing procedure was repeated three times for a total duration of 5 minutes. The 3D printing was carried out using a custom-built extrusion-based 3D printer. All printing processes employed a 19 G nozzle with an inner diameter of approximately 0.75 mm. The printing speed and pneumatic pressure were adjusted appropriately according to the sliced CAD models. The synthesized thermoelectric inks were loaded into syringes (Saejong) and deposited onto graphite substrates under pneumatic pressure control. For the p-type BST, the printed TE legs were dried at around 200°C for more than 12 hours to completely remove glycerol. Subsequent sintering process was performed at 450°C for 5 hours in a tube furnace with a heating rate of 10°C min − 1 . For the n-type BTS, the printed thermoelectric legs were directly sintered without a prior drying step at 500°C for 5 hours in a tube furnace with a heating rate of 1.5°C min − 1 . All the heat treatments were carried out under a nitrogen atmosphere. Characterization of the SHP and AgF-SHP Composite Thin Films The rheological properties of the SHP and AgF–SHP films were characterized using a Discovery Hybrid Rheometer (TA Instruments, New Castle, DE, USA). Frequency sweep tests were carried out at 1% strain over a frequency range of 0.01–10 Hz to evaluate the storage modulus ( G ′), loss modulus ( G ″), and tangent delta (tan δ). The samples were prepared as square films (10×10 mm 2 ), gap distance (0.1 mm), and axial force (0.1 N) were kept constant during all measurements 38 . Thermal stability and phase transitions were analyzed using thermogravimetric analysis (TGA; TG/DTA6100, Seiko, Japan) and differential scanning calorimetry (DSC; DSC 7020, Hitachi, Japan). All measurements were performed under a nitrogen atmosphere (Exstar 6000, Seiko Instruments) with a heating rate of 10°C min − 1 . TGA data were used to determine weight loss and thermal degradation behavior, while DSC thermograms provided information on glass transition and enthalpic changes. Characterization of the 3D-printed TE legs ζ-potential measurements of the BST and BTS inks were conducted using an electrophoretic light scattering (ELS) analyzer (Zetasizer Nano ZS, Malvern Instruments, United Kingdom). The particle dispersions for this analysis were prepared by dispersing the BST and BTS particles in DI water via ultrasonication for at least 30 minutes. The rheological properties of the BST and BTS inks were analyzed using a rotational rheometer (MCR 302e, Anton Paar, Austria) with a 25 mm parallel plate geometry. Frequency sweeps were conducted from 0.05 to 500 rad s⁻¹ at a constant stress of 1 Pa. Amplitude sweeps were performed over a stress range of 0.05–200 Pa at a fixed frequency of 1 rad s⁻¹. All measurements were maintained at 20°C. The temperature-dependent electrical conductivity and Seebeck coefficient were measured using a commercial Seebeck measurement system (LSR-3, Linseis, Germany) over a temperature range from room temperature to 200°C under a helium atmosphere. The thermal conductivity ( κ ) was determined using the relation κ = ρC p D , where \(\:\rho\:\) is the density, C p is the specific heat capacity, and D is the thermal diffusivity. The density of the sintered samples was calculated by measuring their weight and volume after polishing them into a cuboid shape to minimize dimensional measurement errors. The specific heat capacity was estimated using the Dulong–Petit equation, and the thermal diffusivity was obtained through laser flash analysis (LFA500, Linseis, Germany). Simulation of TEG performance The temperature distribution and output voltage of the TE Lego block devices were simulated using the COMSOL software. The electrical and thermal properties of the materials used in the simulation were based on the experimentally measured values. The cold and hot sides of the TE Lego block devices were fixed at 20°C and 70°C, respectively, while a convection coefficient of 5 W m − 2 K − 1 at 25°C was applied to the remaining surfaces. Declarations Competing interests The authors declare no competing interests. Funding This research did receive funding. • Donghee Son received funding from Korea Basic Science Institute; Grant ID RS-2024-00401763. • Jae Sung Son received funding from National Research Foundation of Korea; Grant ID RS-2024-00448499. Author Contribution K.K. and K.P. contributed equally to this work. K.K., K.P., J.E.L., D.S., and J.S.S. designed the experiments, analyzed the data, and wrote the paper. K.K. carried out the synthesis and characterization of TE Lego blocks and the evaluation of devices. K.P. and J.S. carried out the synthesis and characterization of SHP and AgF-SHP. All authors discussed the results and commented on the manuscript. Acknowledgement This work was supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIT) (RS-2024-00448499). This work was also supported by Korea Basic Science Institute (National research Facilities and Equipment Center) grant funded by the Ministry of Science and ICT (No. RS-2024-00401763). Data Availability The data that support the findings of this study are available within the article and its Supplementary Information files. All raw data generated during the current study are available from the corresponding authors upon request. References DiSalvo, F. J. Thermoelectric Cooling and Power Generation. Science ( 1979) 285, 703–706 (1999). Bell, L. E. 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Additional Declarations No competing interests reported. Supplementary Files SupplementaryInformation.pdf Cite Share Download PDF Status: Published Journal Publication published 20 Jan, 2026 Read the published version in npj Flexible Electronics → Version 1 posted Editorial decision: Revision requested 15 Dec, 2025 Reviews received at journal 15 Dec, 2025 Reviews received at journal 08 Dec, 2025 Reviews received at journal 06 Dec, 2025 Reviewers agreed at journal 03 Dec, 2025 Reviewers agreed at journal 03 Dec, 2025 Reviewers agreed at journal 03 Dec, 2025 Reviewers invited by journal 03 Dec, 2025 Editor assigned by journal 27 Nov, 2025 Submission checks completed at journal 23 Nov, 2025 First submitted to journal 18 Nov, 2025 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. 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09:33:46","extension":"html","order_by":13,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":101590,"visible":true,"origin":"","legend":"","description":"","filename":"earlyproof.html","url":"https://assets-eu.researchsquare.com/files/rs-8142150/v1/3625cd1b3f43015a00c4499d.html"},{"id":97534890,"identity":"5c4152b5-1f6e-40dc-8218-29dab6557694","added_by":"auto","created_at":"2025-12-05 13:54:50","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":7176689,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eSchematic illustrations of assemblable TE Lego blocks\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003ea.\u003c/strong\u003e Conceptual illustration of the assemblable TE Lego blocks. \u003cstrong\u003eb. \u003c/strong\u003eSchematic illustration of the fabrication process for the TE Lego blocks, consisting of 3D printing of TE legs, preparation of Lego parts and assembly into TE Lego block. Photographs showing the \u003cstrong\u003ec. \u003c/strong\u003eassembled TE Lego block device, its \u003cstrong\u003ed. \u003c/strong\u003ebending, and \u003cstrong\u003ee. \u003c/strong\u003estretching conditions.\u003c/p\u003e","description":"","filename":"image1.png","url":"https://assets-eu.researchsquare.com/files/rs-8142150/v1/18f301c7d93fbf5e27ca9fdc.png"},{"id":97534887,"identity":"ba8404b5-d382-447c-88e3-8f801de47397","added_by":"auto","created_at":"2025-12-05 13:54:50","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":1126722,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eMaterial properties of the TE Lego block parts\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eStorage modulus (\u003cem\u003eG’\u003c/em\u003e) and Loss modulus (\u003cem\u003eG’’\u003c/em\u003e) of AgF-SHP sample at \u003cstrong\u003ea.\u003c/strong\u003e 25 °C, \u003cstrong\u003eb.\u003c/strong\u003e 50 °C, \u003cstrong\u003ec.\u003c/strong\u003e 75 °C, and \u003cstrong\u003ed.\u003c/strong\u003e100 °C. \u003cstrong\u003ee.\u003c/strong\u003e Tan δ of the AgF-SHP sample at the temperatures of 25, 50, 75, and 100 °C, respectively. \u003cstrong\u003ef.\u003c/strong\u003e Temperature-dependent electrical conductivity of the AgF-SHP sample. Temperature-dependent thermal conductivity of the \u003cstrong\u003eg.\u003c/strong\u003e SHP and \u003cstrong\u003eh.\u003c/strong\u003eAgF-SHP sample. Temperature-dependent \u003cstrong\u003ei.\u003c/strong\u003e electrical conductivity, \u003cstrong\u003ej.\u003c/strong\u003eSeebeck coefficient, \u003cstrong\u003ek.\u003c/strong\u003e thermal conductivity, and \u003cstrong\u003el.\u003c/strong\u003e ZT values of the 3D-printed p-type and n-type TE samples.\u003c/p\u003e","description":"","filename":"image2.png","url":"https://assets-eu.researchsquare.com/files/rs-8142150/v1/b8c4ad79cd7dce8a8d872815.png"},{"id":97671727,"identity":"3a0dfdd0-f661-4db1-8efe-181000946bdc","added_by":"auto","created_at":"2025-12-08 09:32:59","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":3624841,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eMechanical deformation and self-healing properties of the TE Lego block\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eResistance change of the TE Lego block devices under mechanical deformation as a function of \u003cstrong\u003ea.\u003c/strong\u003e bending radius and \u003cstrong\u003eb.\u003c/strong\u003eapplied strain. \u003cstrong\u003ec.\u003c/strong\u003e Photographs of an assembled TE Lego block device, showing its electrical connection status after disassembly into individual blocks and subsequent reassembly. Time-dependent resistance change of the TE Lego block devices after \u003cstrong\u003ed.\u003c/strong\u003e scratching and \u003cstrong\u003ee.\u003c/strong\u003e cutting. \u003cstrong\u003ef.\u003c/strong\u003eCurrent-Voltage curves of the original and self-healed TE Lego block devices. All the white scale bars in the inset photographs represent 5 mm.\u003c/p\u003e","description":"","filename":"image3.png","url":"https://assets-eu.researchsquare.com/files/rs-8142150/v1/04f6752d2d6fcc922678beea.png"},{"id":97671790,"identity":"69eb3bb5-44d2-4e43-96df-03ac7336776e","added_by":"auto","created_at":"2025-12-08 09:33:06","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":4846395,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eLego-like module assembly and reconfiguration\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003ea. \u003c/strong\u003eAs-prepared P-90, P-180, P-270, N-90, N-180, and N-270 TE Lego blocks before assembly and reconfiguration into TE devices for power generation. \u003cstrong\u003eb. \u003c/strong\u003eSchematic illustration of the assembly process for constructing TE Lego block devices with 2, 4, and 6 pairs. Current-voltage curves of \u003cstrong\u003ec. \u003c/strong\u003e2 pairs, \u003cstrong\u003ed. \u003c/strong\u003e4 pairs, and \u003cstrong\u003ee. \u003c/strong\u003e6 pairs of TE Lego block devices under the different temperature differences (\u003cem\u003e∆T\u003c/em\u003e). \u003cstrong\u003ef. \u003c/strong\u003eSchematic illustration of the reconfiguration process for U-, V- and W-shaped TE Lego block devices. Current-voltage curves of \u003cstrong\u003eg. \u003c/strong\u003eU-shaped, \u003cstrong\u003eh. \u003c/strong\u003eV-shaped, and \u003cstrong\u003ei. \u003c/strong\u003eW-shaped TE Lego block devices under different \u003cem\u003e∆T\u003c/em\u003e. All the black scale bars in the inset photographs represent 10 mm.\u003c/p\u003e","description":"","filename":"image4.png","url":"https://assets-eu.researchsquare.com/files/rs-8142150/v1/10e5b6d65235b82737f5fcc8.png"},{"id":101151784,"identity":"daa6c076-12fc-49e6-91f5-271973cdb2d7","added_by":"auto","created_at":"2026-01-26 16:05:29","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":16714121,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-8142150/v1/7303c7cc-95b0-4595-86b3-56d98c158f8f.pdf"},{"id":97534889,"identity":"51bd45ed-79a1-4b09-999a-e6771e8f69e4","added_by":"auto","created_at":"2025-12-05 13:54:50","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"supplement","size":1814866,"visible":true,"origin":"","legend":"","description":"","filename":"SupplementaryInformation.pdf","url":"https://assets-eu.researchsquare.com/files/rs-8142150/v1/ba6dd2976093d0983a4b8594.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Assemblable thermoelectric Lego blocks for reconfigurable, self- healing, and flexible power generators","fulltext":[{"header":"Introduction","content":"\u003cp\u003eThermoelectric (TE) devices, which can directly convert heat into electricity or vice versa, have garnered significant attention as a promising technology for waste heat recovery and solid-state cooling\u003csup\u003e\u003cspan additionalcitationids=\"CR2\" citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e\u003c/sup\u003e. The fundamental principle relies on the Seebeck and Peltier effects, enabling them to operate as clean and quiet energy converters. Conventional TE devices adopt a planar architecture in which multiple pairs of n-type and p-type TE legs are soldered to top and bottom metal electrodes on ceramic substrates. All components are rigid inorganic layers connected electrically in series and thermally in parallel. This architecture resists conformal contact with non-planar heat sources (e.g., pipes or ducts), incurring parasitic thermal losses\u003csup\u003e\u003cspan additionalcitationids=\"CR5\" citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e\u003c/sup\u003e. Moreover, the intrinsic brittleness of the inorganic components renders devices vulnerable to fracture under prolonged vibration or mechanical shock where the failure of a single junction can disable the entire device\u003csup\u003e\u003cspan additionalcitationids=\"CR8 CR9\" citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e\u003c/sup\u003e. Repair or reconfiguration is technically infeasible, typically requiring full disassembly and reassembly of all components.\u003c/p\u003e\u003cp\u003eTo address the inherent limitations of conventional bulk TE devices, flexible TE devices have emerged as compelling alternatives\u003csup\u003e\u003cspan additionalcitationids=\"CR12 CR13\" citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e\u003c/sup\u003e. Their ability to conform to non-planar heat sources markedly improves interfacial heat transfer, while their superior mechanical compliance enhances reliability under external stress, enabling longer operational lifetimes. Additionally, they offer enhanced mechanical reliability under external stresses, ensuring stable performance over a longer operational lifetime. This progress has expanded application areas, particularly in wearable electronics where mechanical flexibility is essential\u003csup\u003e\u003cspan additionalcitationids=\"CR16 CR17 CR18\" citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e\u003c/sup\u003e. More recently, the integration of self-healing functionality\u0026mdash;implemented in electrodes and/or TE legs\u0026mdash;has been proposed to further improve robustness by autonomously repairing microcracks, scratches, and other localized defects, thereby extending service life and reducing maintenance demands\u003csup\u003e\u003cspan additionalcitationids=\"CR21 CR22\" citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e\u003c/sup\u003e. Despite these advances, most studies have concentrated on localized damage repair; leveraging self-healing for device-level reconfiguration along with purposeful structural design remains largely underexplored.\u003c/p\u003e\u003cp\u003eHere, we propose the concept of Lego-like TE leg blocks that can be assembled into devices with arbitrary architecture. Each block functions as an independent, reconfigurable unit featuring self-healing electrodes, enabling the construction of flexible, repairable, and modular TE generators (TEGs) (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ea). To realize this design, we employed a PDMS-based self-healing polymer (SHP) and Ag-flake-dispersed SHP (AgF-SHP) as electrode materials, integrated with 3D-printed (Bi,Sb)\u003csub\u003e2\u003c/sub\u003eTe\u003csub\u003e3\u003c/sub\u003e and Bi\u003csub\u003e2\u003c/sub\u003e(Te,Se)\u003csub\u003e3\u003c/sub\u003e TE legs to form TE Lego blocks (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eb). The assembled devices retained their performance under bending, stretching, and even after cutting and reassembly (Figs.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ec-e), withstanding a bending radius of about 3.4 mm and a stretching strain of up to 40%. Furthermore, the devices could be repeatedly disassembled and reassembled into diverse geometries (U, V, and W shapes) without degradation in power output, demonstrating the reconfiguration capability of the Lego blocks. This concept thus provides TE leg-level assemblability, delivering true architectural freedom and establishing a robust, versatile, and easily repairable platform for next-generation TE technology.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e"},{"header":"Results","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e\u003ch2\u003eFabrication of TE Lego blocks\u003c/h2\u003e\u003cp\u003eTE Lego blocks were fabricated with the 3D-printed TE legs and self-healing AgF\u0026ndash;SHP composite electrodes. The self-healing electrodes were connected to the top and bottom surfaces of TE legs employing conductive Ag adhesive. For TE legs, Bi\u003csub\u003e0.5\u003c/sub\u003eSb\u003csub\u003e1.5\u003c/sub\u003eTe\u003csub\u003e3\u003c/sub\u003e (BST) and Bi\u003csub\u003e2\u003c/sub\u003eTe\u003csub\u003e2.7\u003c/sub\u003eSe\u003csub\u003e0.3\u003c/sub\u003e (BTS) were chosen as the p-type and n-type TE materials, respectively, as their compositions are known to exhibit high TE properties near room temperature\u003csup\u003e\u003cspan additionalcitationids=\"CR25\" citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e\u003c/sup\u003e. We fabricated three different types of TE Lego blocks for the device assembly, depending on the direction of electrodes, 90\u0026deg;, 180\u0026deg;, and 270\u0026deg;, which allows the integration of TE Lego blocks into diverse architectures of devices. We denoted the type of the TE Lego blocks depending on their carrier type of the TE materials and the top and bottom electrode angle; e.g. P-90, N-90, P-180, N-180, P-270, and N-270. These components are then assembled as desired to fabricate the TE Lego blocks.\u003c/p\u003e\u003cp\u003eThe SHP and AgF-SHP composite films were fabricated by adapting a previously reported procedure\u003csup\u003e\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e\u003c/sup\u003e. A homogeneous SHP solution was prepared by dissolving pre-synthesized SHP in chloroform (CHCl\u003csub\u003e3\u003c/sub\u003e), which was then cast and subsequently dried to fabricate the film (Supplementary Fig.\u0026nbsp;1). The SHP itself was prepared according to the previous literature method\u003csup\u003e\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e\u003c/sup\u003e. The self-healing efficiency can be enhanced through thermal or plasma treatments (Methods). For the electrode parts of the TE Lego block, an SHP film was cut into a \"U\" shape. A AgF-SHP film with the rectangular-shaped pattern was then inserted into the center opening of the U-shaped SHP film, resulting in a final square geometry for the electrode assembly. The center part of the block was constructed by stacking multiple layers of hollow-squared cut SHP films, creating an internal cavity designed to house the TE leg. Finally, the complete TE Lego block was assembled by integrating the upper electrode part, the center part containing a 3D-printed TE leg fabricated as described in a later section, and the lower electrode part.\u003c/p\u003e\u003cp\u003eFor the production of TE leg materials, we used the extrusion-based 3D printing method with the 3D-printable inks of the TE particle colloids with desired rheological properties (Supplementary Fig.\u0026nbsp;2). We used the modified method of that developed by our group previously\u003csup\u003e\u003cspan additionalcitationids=\"CR30 CR31 CR32\" citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e\u003c/sup\u003e. Briefly, well-dispersed colloidal ink was prepared by vigorously mixing mechanically alloyed BST and BTS particles obtained via ball milling in a glycerol medium. The ball-milled BST and BTS particles exhibited high zeta potential values of -27.6 mV and \u0026minus;\u0026thinsp;32.8 mV, respectively, indicating a significant surface charge on the synthesized particles. The TE colloidal ink was formulated with a high particle loading of approximately 30 vol% to achieve the high viscoelasticity required for subsequent 3D printing. The suitability of the formulated TE colloidal inks for 3D printing was verified by measuring their viscoelastic properties using a rheometer. Under an angular frequency sweep, the complex viscosity at 0.06 rad\u0026middot;s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e was approximately 6.59\u0026times;10\u003csup\u003e5\u003c/sup\u003e Pa\u0026middot;s for the BST ink and 8.57\u0026times;10\u003csup\u003e5\u003c/sup\u003e Pa\u0026middot;s for the BTS ink. Furthermore, in a shear stress sweep condition, the storage modulus values prior to the yield point ranged from 1.21\u0026ndash;1.41\u0026times;10\u003csup\u003e4\u003c/sup\u003e Pa for the BST ink and 2.25\u0026ndash;2.66\u0026times;10\u003csup\u003e4\u003c/sup\u003e Pa for the BTS ink. These values are comparable to those of previously reported 3D direct-writable Bi\u003csub\u003e2\u003c/sub\u003eTe\u003csub\u003e3\u003c/sub\u003e-based inks formulated without additives. These inks were 3D-printed to produce several tens of TE legs in a single pass (Supplementary Fig.\u0026nbsp;3). The subsequent heat treatment at 450 \u003csup\u003eo\u003c/sup\u003eC generated well-sintered BST and BTS TE legs. Furthermore, the sintered p-type and n-type legs were found to display nearly identical volume shrinkage ratios (Supplementary Fig.\u0026nbsp;4), which simplifies the fabrication of dimensionally controlled TE Lego blocks.\u003c/p\u003e\u003c/div\u003e\n\u003ch3\u003eMaterial properties of the TE leg block components\u003c/h3\u003e\n\u003cp\u003eTo utilize the self-healing AgF-SHP composites as TE power generation that requires the operation at high temperatures, we investigated various properties of these composites at elevated temperatures. First, the rheological behavior of AgF\u0026ndash;SHP composites by monitoring their shear stress responses at 25, 50, 75, and 100\u0026deg;C under oscillatory frequencies ranging from 0.01 to 100 Hz (Figs.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ea-e). The thermal properties of AgF\u0026ndash;SHP composites with varying Ag flake loadings consistently exhibited high storage and loss modulus values, suggesting superior thermal resistance compared to conventional amorphous polymers attributed to the strong hydrogen bonding interactions within the polyurea framework. Notably, the sample with SHP: AgF of 1:4 in the weight ratio, employed as the electrode, maintained stable behavior in the range of 25\u0026ndash;50\u0026deg;C indicating the preservation of viscoelastic balance, while regions with tangent δ (tan δ\u0026thinsp;=\u0026thinsp;\u003cem\u003eG''\u003c/em\u003e/\u003cem\u003eG'\u003c/em\u003e) values exceeding 1 emerged at temperatures above 75\u0026deg;C, signifying a transition toward a more viscous-dominated response. In addition, although increasing the amount of AgFs makes the AgF-SHP composite stiffer, we found that variations in AgF weight loading ratios (1:1, 1:2, and 1:3) exerted only a negligible influence on the tan δ (Supplementary Fig.\u0026nbsp;5). This indicates that the damping characteristics of the composites were largely preserved regardless of filler content, suggesting that the incorporation between Ag-flakes and SHP does not substantially perturb the intrinsic rheological characteristics of SHP.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eDifferential scanning calorimetry (DSC) was also conducted in the temperature range of \u0026minus;\u0026thinsp;80 to 80\u0026deg;C for AgF\u0026ndash;SHP composites with SHP:AgF weight ratios of 1:1, 1:2, 1:3, and 1:4 (Supplementary Fig.\u0026nbsp;6). All the composites exhibited only minimal thermal transitions below 0\u0026deg;C, confirming the amorphous behavior of the AgF\u0026ndash;SHP backbone. Furthermore, the variation in heat flow progressively decreased when the Ag-flakes content increased. Since DSC quantifies the amount of heat absorption or released during temperature fluctuations, these results indicate a reduction in absolute heat flow variation with increasing Ag-flakes ratio. Importantly, no evidence of oxidation\u0026ndash;reduction processes between Ag-flakes and SHP was detected within the investigated temperature range, and no structural changes in either component were observed below 80\u0026deg;C. These findings are in agreement with previously reported results for similar polymer-filler systems\u003csup\u003e\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e\u003c/sup\u003e. Thermogravimetric analysis (TGA) further verified the excellent thermal stability of the AgF-SHP where no significant weight loss or thermal degradation was observed up to 220\u0026deg;C (Supplementary Fig.\u0026nbsp;7). Collectively, the combined DSC and TGA results confirm that the AgF-SHP composite preserves a stable structure under repeated thermal cycling between 25 and 75\u0026deg;C. These attributes underscore its potential utility in TEG platforms at elevated temperatures.\u003c/p\u003e\u003cp\u003eWe investigated the temperature-dependent electrical conductivity (\u003cem\u003eσ\u003c/em\u003e) of the as-synthesized AgF-SHP composite samples within the typical operating temperature range of TEGs, from 20\u0026deg;C to 70\u0026deg;C (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ef). The measurement results showed that the electrical conductivity of the AgF-SHP composite reached a maximum value of approximately 141 S cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e at room temperature. As the temperature increased, the electrical conductivity decreased, reaching approximately 101 S cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e at 70\u0026deg;C. This behavior is presumably attributed to the metallic property of the AgFs, which are the primary conductive component of the composite. Furthermore, the thermal conductivities (\u003cem\u003eκ\u003c/em\u003e) measurement was conducted for both the pristine SHP and the AgF-SHP composite samples (Figs.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eg and \u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eh). For the pristine SHP sample, which contains no dispersed silver flakes, the thermal conductivity showed a maximum value of approximately 0.14 W m\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e K\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e at room temperature, decreasing to approximately 0.11 W m\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e K\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e at 70\u0026deg;C. This trend of decreasing thermal conductivity with increasing temperature is consistent with the reported intrinsic material properties of polydimethylsiloxane (PDMS)\u003csup\u003e\u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e,\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e\u003c/sup\u003e, which is the main component of the SHP. In the case of the AgF-SHP composite sample, it shows the maximum thermal conductivity value of about 1.10 W m\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e K\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e at room temperature, which similarly decreased as the temperature increases, reaching a value of about 0.98 W m\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e K\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e at 70\u0026deg;C. This appears to be a phenomenon attributed to the metallic properties of the silver flakes, as observed previously. Notably, the thermal conductivity of the AgF-SHP composite sample was approximately one order of magnitude higher than that of the pristine SHP. This significant increase is ascribed to the extremely high thermal conductivity of the dispersed silver particles within the composite sample\u003csup\u003e\u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e\u003cp\u003eWe also characterized the temperature-dependent electrical and thermal properties of the 3D-printed BST and BTS samples. Specifically, the electrical conductivities at room temperature for p-type BST and n-type BTS were about 4,240 S cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e and 12,500 S cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, respectively (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ei). Both samples exhibited the characteristic behavior of degenerate semiconductors, with the electrical conductivity gradually decreasing as the temperature increased. Regarding the Seebeck coefficient, the p-type BST sample showed a value of approximately 221.5 \u0026micro;V K\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e at room temperature, which gradually increased to a peak value of approximately 242.7 \u0026micro;V K⁻\u0026sup1; at around 100\u0026deg;C, while the n-type BTS sample showed a tendency for its absolute value to increase with temperature within the range of -110.3 to -147.0 \u0026micro;V K\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ej). Consequently, the resulting maximum power factor values for the BST and BTS materials were 2.08 and 1.58 mW m\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e K\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e, respectively (Supplementary Fig.\u0026nbsp;8).\u003c/p\u003e\u003cp\u003eThe thermal conductivity of the BST sample increased with temperature, ranging from 0.62 to 0.96 W m\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e K\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, whereas the thermal conductivity of the BTS sample showed weak temperature dependence, remaining between 1.00 and 1.08 W m\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e K\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ek). These values are comparatively lower than those of their bulk samples, which is attributed to the inherent high porosity of samples (26% for BST and 21% for BTS) fabricated through the 3D printing process. Finally, the figure of merit (\u003cem\u003eZT\u003c/em\u003e) values of the TE samples were calculated from the measured electrical and thermal properties (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003el). The p-type BST achieved a \u003cem\u003eZT\u003c/em\u003e of 1.02 at room temperature and a peak \u003cem\u003eZT\u003c/em\u003e of 1.07 at approximately 50\u0026deg;C. The n-type BTS exhibited a \u003cem\u003eZT\u003c/em\u003e of 0.43 at room temperature, reaching a maximum value of approximately 0.65 at around 175\u0026deg;C. These values are comparable to those of the previously reported 3D-printed materials with corresponding compositions\u003csup\u003e\u003cspan additionalcitationids=\"CR25\" citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e\n\u003ch3\u003eMechanical deformation and self-healing properties of the TE Lego block\u003c/h3\u003e\n\u003cp\u003eThe mechanical deformation properties of the assembled TE device made of the TE Lego blocks were initially characterized using a uniaxial stretcher to perform bending and stretching tests at room temperature. During the bending test, which was performed by progressively decreasing the stretcher's gap, the electrical resistance of the device was slightly decreased as the bending radius decreased (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ea). Specifically, the electrical resistance continuously dropped until a minimum bending radius of approximately 3.4 mm was reached, at which point the resistance was about 17% lower than that of the original flat device. As previously reported, this reduction is attributed to the electrical self-boosting effect in the AgF-SHP, which enhances its electrical conductivity\u003csup\u003e\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e\u003c/sup\u003e. This is considered the primary cause for the observed reduction in total device resistance. In the stretching test, performed by increasing the stretcher's gap, the device's electrical resistance first decreased up to about 10% strain (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eb). This behavior is likely attributed to the self-boosting effect in the AgF-SHP sample at low strains up to about 10%, as previously observed. With further elongation, the electrical resistance began to increase and returned to its original value at about 30% strain. Beyond this point, a sharp rise in electrical resistance occurred. However, upon further stretching, the mechanical adhesion between the AgF-SHP sample and the 3D-printed TE leg appears to weaken. This would increase the contact resistance, leading to the observed rise in the device's total electrical resistance. Thus, it was confirmed that even under mechanical deformation conditions of bending and stretching, there was no significant difference in the performance of the TE device assembled from TE Lego blocks.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eWe also investigated the self-healing capability of the AgF-SHP electrode (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ec), as this property is a key factor enabling the \u0026ldquo;Lego-like\u0026rdquo; behavior of the TE Lego block devices. Initially, we assembled a 2\u0026times;2 array TE device by properly arranging four TE Lego blocks in an electrically continuous connection. Upon their disassembly into individual blocks, the electrical connection was interrupted. However, after subsequent reassembly, the AgF-SHP electrodes underwent self-healing, and the final TE device successfully re-established their electrical connectivity.\u003c/p\u003e\u003cp\u003eTo quantitatively investigate the self-healing behavior of the AgF-SHP electrode within the TE Lego block, we monitored the evolution of electrical resistance following two types of damage, surface scratching and complete cutting. When the electrode was scratched, its resistance immediately increased by approximately 45% yet exhibited a rapid recovery (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ed). Remarkably, the electrical resistance returned to within 2% of its original value within 200 sec, without external stimuli applied to facilitate the healing process. In the case of cutting, the complete detachment of the assembled TE device to individual TE Lego blocks, a total loss of electrical connectivity was observed (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ee). Upon re-establishing contact between the severed AgF-SHP interfaces in their proper orientation, an immediate self-healing process restored the electrical conductivity of the device. Furthermore, the application of gentle pressure after reassembly not only accelerated the self-healing speed but also enabled the electrical performance to recover to a level nearly identical to its original state.\u003c/p\u003e\u003cp\u003eCapitalizing on these self-healing capabilities, we compared the power generation performance of an original TE device composed of two pairs of p-type and n-type TE Lego blocks with that of a self-healed device after cutting (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ef). At a temperature difference (\u003cem\u003e∆T\u003c/em\u003e) of 50\u0026deg;C, the original device exhibited an open-circuit voltage (\u003cem\u003eV\u003c/em\u003e\u003csub\u003eoc\u003c/sub\u003e) of approximately 15.4 mV and an output power of approximately 10.94 \u0026micro;W. After the self-healing process, the re-assembled device demonstrated a \u003cem\u003eV\u003c/em\u003e\u003csub\u003eoc\u003c/sub\u003e of approximately 15.3 mV and the output power of approximately 10.36 \u0026micro;W under the same \u003cem\u003e∆T.\u003c/em\u003e These results represent performance deviations of only 0.7% and 5.6%, respectively, from the original values. This high degree of performance recovery demonstrates that it is possible to assemble and reconfigure these TE Lego blocks into new TE devices.\u003c/p\u003e\n\u003ch3\u003eLego-like device assembly and reconfiguration of TEG\u003c/h3\u003e\n\u003cp\u003eA key characteristic of conventional Lego blocks is their ability to not only be assembled, but also to be disassembled and reconfigured into new structures. To evaluate if our newly proposed TE Lego blocks show these \"Lego-like\" characteristics, we first fabricated individual blocks and then constructed TE devices using them in various combinations. Prior to TE device fabrication, a total of twelve TE Lego blocks was prepared, consisting of two blocks each of six different types: P-90, P-180, P-270, N-90, N-180, and N-270 (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ea). These blocks were then used for the assembly and reconfiguration into TE devices for the power generation. Unlike conventional TE devices which generally use Cu electrodes with extremely high thermal conductivity, the TE Lego block devices use AgF-SHP samples with very low thermal conductivity. Consequently, the actual \u003cem\u003e∆T\u003c/em\u003e created across the TE legs when subjected to high and low temperatures on either side of the device could be smaller than that observed in that of a conventional device (Supplementary Fig.\u0026nbsp;9). Therefore, to ensure sufficient \u003cem\u003e∆T\u003c/em\u003e and enhance output power, we prepared the TE legs with a relatively high aspect ratio of 1.5 for the power generation application.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eThe assembly test of the TE Lego block array was first conducted (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eb). We progressively assembled 2-pairs (4\u0026times;1 array), 4-pairs (4\u0026times;2 array), and 6-pair (4\u0026times;3 array) TE devices, starting from an initial 2-pair device, while ensuring the electrical connectivity of the entire device was maintained. Subsequently, a temperature difference was applied across both sides of each device configuration, and the output voltage and output power were measured. During the power-generation test, the hot side was heated using a ceramic plate whose temperature could be controlled by the applied current, while the cold side was cooled with a Cu block maintained at 20\u0026deg;C by a cooling chiller. Measurements of hot- and cold-side temperatures, output voltage, and device resistance were carried out under equivalent \u003cem\u003e∆T\u003c/em\u003e conditions (Figs.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ec\u0026ndash;e). As the hot-side temperature increased, the \u003cem\u003e∆T\u003c/em\u003e across the devices increased correspondingly. In each pair device, the output voltage exhibited a linear dependence with increasing \u003cem\u003e∆T\u003c/em\u003e, and the output voltage increased proportionally with the number of pairs in the device under the same \u003cem\u003e∆T\u003c/em\u003e. Moreover, the quadratic dependence of output power further supported the reliability of the measurements. Consequently, a maximum output voltage of 42.2 mV and an output power of 28.7 \u0026micro;W were achieved at the maximum temperature difference of 50\u0026deg;C in the 4\u0026times;3 array 6-pairs device. These measured results were also confirmed to be consistent with the output voltage of simulation results under the same environmental conditions (Supplementary Fig.\u0026nbsp;10).\u003c/p\u003e\u003cp\u003eThe reconfiguration capability was also demonstrated using the same set of TE Lego blocks. Unlike conventional TEGs which are rigid cuboid arrays, the TE Lego block generator allows for a high degree of freedom in device architecture, as long as electrical series connectivity is maintained. Specifically, the twelve p-type and n-type TE Lego blocks was assembled into a U-shaped TE device. The blocks were then disassembled and reassembled to reconfigure the device into V- and W-shaped architectures (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ef). These configurations maintain electrical serial connection as the p-type and n-type legs are connected alternately. Furthermore, if a change in device design or dimension is required, reconfiguration is easily accomplished by disassembly of the individual TE Lego blocks and forming new structures (Supplementary Fig.\u0026nbsp;11). The TE power generation performance of the U-, V- and W-shaped TE Lego block generators were measured by applying a \u003cem\u003e∆T\u003c/em\u003e across both sides using the same method as before (Figs.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eg\u0026ndash;i). At a \u003cem\u003e∆T\u003c/em\u003e of approximately 50\u0026deg;C, all three devices exhibited \u003cem\u003eV\u003c/em\u003e\u003csub\u003eoc\u003c/sub\u003e values ranging from 42.5 to 46.5 mV, confirming no significant difference in their device performance (Supplementary Fig.\u0026nbsp;12). The output power ranged from 26.38 \u0026micro;W to 32.78 \u0026micro;W under the same \u003cem\u003e∆T.\u003c/em\u003e While this may seem like a relatively large variation, considering that the output power is proportional to the square of the voltage, it indicates that the difference in the total electrical resistance of the device was minimal. These results demonstrate that the use of TE Lego blocks for TE device construction provides broad structural flexibility without significant performance degradation.\u003c/p\u003e"},{"header":"Discussion","content":"\u003cp\u003eWe have demonstrated modular, “Lego-like” TE blocks that enable on-demand assembly, repair, and reconfiguration while providing mechanical flexibility and electrical self-healing. Each block combines 3D-printed TE legs with conductive, self-healing AgF-SHP electrodes. The self-healing capability—validated by scratch and detachment tests—reliably restores electrical connection after disassembly and reassembly, underpinning robust reconfigurability. Assembled devices maintain stable performance under substantial bending and tensile strain, and reconfiguration into diverse architectures (e.g., U-, V-, and W-shapes) proceeds without significant loss of power output. Collectively, this freely reconfigurable and repairable approach overcomes limitations of conventional rigid TEGs and paves the way for customizable, durable, and structurally adaptable TE energy-harvesting systems.\u003c/p\u003e\u003cdiv id=\"Sec8\" class=\"Section2\"\u003e\u003cdiv id=\"Sec9\" class=\"Section3\"\u003e\u003c/div\u003e\u003c/div\u003e"},{"header":"Methods","content":"\u003ch2\u003eMaterials\u003c/h2\u003e\u003cp\u003e4,4′-Methylenebis(phenyl isocyanate) (MDI) and isophorone diisocyanate (IPDI) were sourced from TCI Chemicals. Ag-flakes (AgFs, DSF500MWZ-S) were supplied from Daejoo Electronics. Bis(3-aminopropyl)-terminated poly(dimethylsiloxane) (H\u003csub\u003e2\u003c/sub\u003eN-PDMS-NH\u003csub\u003e2\u003c/sub\u003e, M\u003csub\u003en\u003c/sub\u003e = 5000–7000) was a product of Gelest. Bismuth (Bi), Antimony (Sb), Tellurium (Te), and Selenium (Se) granules (all 99.999% purity) were purchased from Thermoelectric Total Solution. All other chemicals and solvents, including octadecyltrichlorosilane (OTS), octadecyltrimethoxysilane (OTMS), and glycerol (\u0026gt; 99.5%), were purchased from Sigma-Aldrich. All the reagents were used as received without further purification.\u003c/p\u003e\n\u003ch3\u003eFabrication of SHP and AgF–SHP Composite Thin Films\u003c/h3\u003e\n\u003cp\u003eBefore fabricating SHP films, SHP was synthesized via a urea coupling reaction following previously reported protocol\u003csup\u003e\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e\u003c/sup\u003e. In a typical procedure, Et\u003csub\u003e3\u003c/sub\u003eN (10 mL) was added to a solution of H\u003csub\u003e2\u003c/sub\u003eN-PDMS-NH\u003csub\u003e2\u003c/sub\u003e (100 g) in CHCl\u003csub\u003e3\u003c/sub\u003e (400 mL) under an argon atmosphere at 0\u0026deg;C. After 1 h of stirring, a solution of MDI (2.0 g) and IPDI (2.7 g) in CHCl\u003csub\u003e3\u003c/sub\u003e (10 mL) was introduced dropwise. The reaction mixture was stirred for an additional 1 h at 0\u0026deg;C, gradually warmed to room temperature, and allowed to proceed for 4 days. Excess isocyanates were quenched by the addition of MeOH (15 mL), followed by 30 min of stirring. The crude product was concentrated, precipitated in MeOH (60 mL), filtered, and thoroughly washed with CHCl\u003csub\u003e3\u003c/sub\u003e.\u003c/p\u003e\u003cp\u003eSilicon dioxide wafer (SiO\u003csub\u003e2\u003c/sub\u003e) was functionalized with OTS as previously described\u003csup\u003e\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e\u003c/sup\u003e. The slides were sequentially cleaned with acetone and isopropyl alcohol, followed by oxygen plasma treatment (100 W, 200 mTorr, 2 min; Scientific Engineering, Korea). Substrates were immersed in a 0.5% (v/v) OTS/n-hexane solution for 1 h, rinsed with ethanol, and dried under nitrogen. Annealing was carried out on a hot plate at 120\u0026deg;C for 30 min, followed by sonication in CHCl\u003csub\u003e3\u003c/sub\u003e for 5 min to remove unbound silane residues.\u003c/p\u003e\u003cp\u003eThe SHP and AgF\u0026ndash;SHP composite films were fabricated following a modified version of our previously reported protocol.\u003csup\u003e\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e\u003c/sup\u003e Synthesized SHP was dissolved in CHCl\u003csub\u003e3\u003c/sub\u003e (2 g/10 mL) and stirred for 1 h to obtain a homogeneous solution. AgFs were then added at different weight ratios (1:1 to 1:4, corresponding to 2\u0026ndash;8 g of AgFs), followed by 30 min of stirring. The mixture was cast onto OTMS-treated SiO\u003csub\u003e2\u003c/sub\u003e wafers and dried at room temperature for 1 h. After drying, the resulting SHP and AgF-SHP thin films were easily detached from the OTMS-functionalized SiO\u003csub\u003e2\u003c/sub\u003e wafer substrate. Film thicknesses were measured using a surface profiler (Dektak 150, Bruker).\u003c/p\u003e\u003cp\u003eSHP-surface treatment based on photolithography was carried out using a mask aligner (MA6 Gen4, SUSS MicroTec SE, NFEC-2025-08-307674, Germany), operated at the i-line (365 nm). Wedge-error compensation (WEC) was optimised prior to exposure, and vacuum contact at was employed to minimise mask\u0026ndash;substrate tilt. A target exposure dose of 322 mJ cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e was used.\u003c/p\u003e\u003cdiv id=\"Sec11\" class=\"Section2\"\u003e\u003ch2\u003eFabrication of 3D-printed TE legs\u003c/h2\u003e\u003cp\u003eThe p-type BST and n-type BTS TE particles with compositions of Bi\u003csub\u003e0.5\u003c/sub\u003eSb\u003csub\u003e1.5\u003c/sub\u003eTe\u003csub\u003e3\u003c/sub\u003e and Bi\u003csub\u003e2\u003c/sub\u003eTe\u003csub\u003e2.8\u003c/sub\u003eSe\u003csub\u003e0.3\u003c/sub\u003e, respectively, were synthesized by mechanical alloying using a planetary ball mill (Planetary Mono Mill, PULVERISETTE 6) operated at 450 rpm for 11 hours. The ball milling process was performed in a zirconia jar with 5 mm zirconia balls at a 5:1 ball-to-powder weight ratio. The resulting powders were then sieved through a 45 \u0026micro;m mesh to obtain fine particles with a controlled size distribution.\u003c/p\u003e\u003cp\u003eThe p-type and n-type TE inks were prepared by mixing 9.2 g of ball-milled BST particles and 10.8 g of ball-milled BTS particles, respectively, with 4 g of glycerol using a planetary centrifugal mixer (ARM-100, Thinky). The mixing procedure was repeated three times for a total duration of 5 minutes. The 3D printing was carried out using a custom-built extrusion-based 3D printer. All printing processes employed a 19 G nozzle with an inner diameter of approximately 0.75 mm. The printing speed and pneumatic pressure were adjusted appropriately according to the sliced CAD models. The synthesized thermoelectric inks were loaded into syringes (Saejong) and deposited onto graphite substrates under pneumatic pressure control.\u003c/p\u003e\u003cp\u003eFor the p-type BST, the printed TE legs were dried at around 200\u0026deg;C for more than 12 hours to completely remove glycerol. Subsequent sintering process was performed at 450\u0026deg;C for 5 hours in a tube furnace with a heating rate of 10\u0026deg;C min\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e. For the n-type BTS, the printed thermoelectric legs were directly sintered without a prior drying step at 500\u0026deg;C for 5 hours in a tube furnace with a heating rate of 1.5\u0026deg;C min\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e. All the heat treatments were carried out under a nitrogen atmosphere.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec12\" class=\"Section2\"\u003e\u003ch2\u003eCharacterization of the SHP and AgF-SHP Composite Thin Films\u003c/h2\u003e\u003cp\u003eThe rheological properties of the SHP and AgF\u0026ndash;SHP films were characterized using a Discovery Hybrid Rheometer (TA Instruments, New Castle, DE, USA). Frequency sweep tests were carried out at 1% strain over a frequency range of 0.01\u0026ndash;10 Hz to evaluate the storage modulus (\u003cem\u003eG\u003c/em\u003e\u0026prime;), loss modulus (\u003cem\u003eG\u003c/em\u003e\u0026Prime;), and tangent delta (tan δ). The samples were prepared as square films (10\u0026times;10 mm\u003csup\u003e2\u003c/sup\u003e), gap distance (0.1 mm), and axial force (0.1 N) were kept constant during all measurements\u003csup\u003e\u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e38\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e\u003cp\u003eThermal stability and phase transitions were analyzed using thermogravimetric analysis (TGA; TG/DTA6100, Seiko, Japan) and differential scanning calorimetry (DSC; DSC 7020, Hitachi, Japan). All measurements were performed under a nitrogen atmosphere (Exstar 6000, Seiko Instruments) with a heating rate of 10\u0026deg;C min\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e. TGA data were used to determine weight loss and thermal degradation behavior, while DSC thermograms provided information on glass transition and enthalpic changes.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec13\" class=\"Section2\"\u003e\u003ch2\u003eCharacterization of the 3D-printed TE legs\u003c/h2\u003e\u003cp\u003eζ-potential measurements of the BST and BTS inks were conducted using an electrophoretic light scattering (ELS) analyzer (Zetasizer Nano ZS, Malvern Instruments, United Kingdom). The particle dispersions for this analysis were prepared by dispersing the BST and BTS particles in DI water via ultrasonication for at least 30 minutes. The rheological properties of the BST and BTS inks were analyzed using a rotational rheometer (MCR 302e, Anton Paar, Austria) with a 25 mm parallel plate geometry. Frequency sweeps were conducted from 0.05 to 500 rad s⁻\u0026sup1; at a constant stress of 1 Pa. Amplitude sweeps were performed over a stress range of 0.05\u0026ndash;200 Pa at a fixed frequency of 1 rad s⁻\u0026sup1;. All measurements were maintained at 20\u0026deg;C.\u003c/p\u003e\u003cp\u003eThe temperature-dependent electrical conductivity and Seebeck coefficient were measured using a commercial Seebeck measurement system (LSR-3, Linseis, Germany) over a temperature range from room temperature to 200\u0026deg;C under a helium atmosphere. The thermal conductivity (\u003cem\u003eκ\u003c/em\u003e) was determined using the relation \u003cem\u003eκ\u003c/em\u003e\u0026thinsp;=\u0026thinsp;\u003cem\u003eρC\u003c/em\u003e\u003csub\u003ep\u003c/sub\u003e\u003cem\u003eD\u003c/em\u003e, where \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\rho\\:\\)\u003c/span\u003e\u003c/span\u003e is the density, \u003cem\u003eC\u003c/em\u003e\u003csub\u003ep\u003c/sub\u003e is the specific heat capacity, and \u003cem\u003eD\u003c/em\u003e is the thermal diffusivity. The density of the sintered samples was calculated by measuring their weight and volume after polishing them into a cuboid shape to minimize dimensional measurement errors. The specific heat capacity was estimated using the Dulong\u0026ndash;Petit equation, and the thermal diffusivity was obtained through laser flash analysis (LFA500, Linseis, Germany).\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec14\" class=\"Section2\"\u003e\u003ch2\u003eSimulation of TEG performance\u003c/h2\u003e\u003cp\u003eThe temperature distribution and output voltage of the TE Lego block devices were simulated using the COMSOL software. The electrical and thermal properties of the materials used in the simulation were based on the experimentally measured values. The cold and hot sides of the TE Lego block devices were fixed at 20\u0026deg;C and 70\u0026deg;C, respectively, while a convection coefficient of 5 W m\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e K\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e at 25\u0026deg;C was applied to the remaining surfaces.\u003c/p\u003e\u003c/div\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003ch2\u003eCompeting interests\u003c/h2\u003e\u003cp\u003eThe authors declare no competing interests.\u003c/p\u003e\u003c/p\u003e\u003ch2\u003eFunding\u003c/h2\u003e\u003cp\u003eThis research did receive funding.\u003c/p\u003e\u003cp\u003e\u0026bull; Donghee Son received funding from Korea Basic Science Institute; Grant ID RS-2024-00401763.\u003c/p\u003e\u003cp\u003e\u0026bull; Jae Sung Son received funding from National Research Foundation of Korea; Grant ID RS-2024-00448499.\u003c/p\u003e\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003eK.K. and K.P. contributed equally to this work. K.K., K.P., J.E.L., D.S., and J.S.S. designed the experiments, analyzed the data, and wrote the paper. K.K. carried out the synthesis and characterization of TE Lego blocks and the evaluation of devices. K.P. and J.S. carried out the synthesis and characterization of SHP and AgF-SHP. All authors discussed the results and commented on the manuscript.\u003c/p\u003e\u003ch2\u003eAcknowledgement\u003c/h2\u003e\u003cp\u003eThis work was supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIT) (RS-2024-00448499). This work was also supported by Korea Basic Science Institute (National research Facilities and Equipment Center) grant funded by the Ministry of Science and ICT (No. RS-2024-00401763).\u003c/p\u003e\u003ch2\u003eData Availability\u003c/h2\u003e\u003cp\u003eThe data that support the findings of this study are available within the article and its Supplementary Information files. All raw data generated during the current study are available from the corresponding authors upon request.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eDiSalvo, F. J. Thermoelectric Cooling and Power Generation. \u003cem\u003eScience (\u003c/em\u003e1979) 285, 703\u0026ndash;706 (1999).\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eBell, L. E. Cooling, Heating, Generating Power, and Recovering Waste Heat with Thermoelectric Systems. \u003cem\u003eScience (1979)\u003c/em\u003e 321, 1457\u0026ndash;1461 (2008).\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eSnyder, G. J. \u0026amp; Toberer, E. S. Complex thermoelectric materials. \u003cem\u003eNat Mater\u003c/em\u003e 7, 105\u0026ndash;114 (2008).\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eHe, R., Schierning, G. \u0026amp; Nielsch, K. 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Although recent incorporation of flexible or stretchable polymeric components has improved mechanical deformability, these integrated architectures cannot be modified for new functions or restored. In this study, we propose the concept of Lego-like thermoelectric leg blocks that enable on-demand repair and reconfiguration via modular assembly. Each block operates as an independent unit comprising PDMS-based, self-healing Ag-flake-embedded composite electrodes and 3D-printed BiSbTe and BiTeSe thermoelectric legs, yielding flexible, repairable, and modular devices. Assembled devices preserve performance under bending (radius\u0026thinsp;\u0026asymp;\u0026thinsp;3.4 mm), stretching (40%), and even after cutting and reassembly. Moreover, repeated disassembly/reassembly into diverse geometries proceeds without measurable loss in power output. Our Lego-like blocks provide a versatile thermoelectric platform that combines flexibility, reparability, and reconfigurability.\u003c/p\u003e","manuscriptTitle":"Assemblable thermoelectric Lego blocks for reconfigurable, self- healing, and flexible power generators","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-12-05 13:54:45","doi":"10.21203/rs.3.rs-8142150/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2025-12-16T01:45:55+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-12-15T05:19:09+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-12-08T08:03:56+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-12-06T10:48:20+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"339283340401562768413756519217722139075","date":"2025-12-04T02:18:18+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"170706590645688577686858698137976940665","date":"2025-12-03T21:54:10+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"107025038447847171002661592934102041573","date":"2025-12-03T14:37:56+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2025-12-03T14:30:49+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2025-11-27T22:57:24+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2025-11-23T06:53:04+00:00","index":"","fulltext":""},{"type":"submitted","content":"npj Flexible Electronics","date":"2025-11-18T07:08:57+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":"a049d24e-acde-4b61-85c6-3d5970fed17e","owner":[],"postedDate":"December 5th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[{"id":59061088,"name":"Physical sciences/Energy science and technology"},{"id":59061089,"name":"Physical sciences/Engineering"},{"id":59061090,"name":"Physical sciences/Materials science"}],"tags":[],"updatedAt":"2026-01-26T16:01:28+00:00","versionOfRecord":{"articleIdentity":"rs-8142150","link":"https://doi.org/10.1038/s41528-026-00534-8","journal":{"identity":"npj-flexible-electronics","isVorOnly":false,"title":"npj Flexible Electronics"},"publishedOn":"2026-01-20 15:57:14","publishedOnDateReadable":"January 20th, 2026"},"versionCreatedAt":"2025-12-05 13:54:45","video":"","vorDoi":"10.1038/s41528-026-00534-8","vorDoiUrl":"https://doi.org/10.1038/s41528-026-00534-8","workflowStages":[]},"version":"v1","identity":"rs-8142150","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-8142150","identity":"rs-8142150","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}