Face-to-Face Type Giant Dimeric Donors Synergistically Improve the Stability and Efficiency of Organic Solar Cells

Face-to-Face Type Giant Dimeric Donors Synergistically Improve the Stability and Efficiency of Organic Solar Cells | Authorea try { document.documentElement.classList.add('js'); } catch (e) { } var _gaq = _gaq || []; _gaq.push(['_setAccount', 'G-8VDV14Y67G']); _gaq.push(['_trackPageview']); (function() { var ga = document.createElement('script'); ga.type = 'text/javascript'; ga.async = true; ga.src = ('https:' == document.location.protocol ? 'https://ssl' : 'http://www') + '.google-analytics.com/ga.js'; var s = document.getElementsByTagName('script')[0]; s.parentNode.insertBefore(ga, s); })(); Skip to main content Preprints Collections Wiley Open Research IET Open Research Ecological Society of Japan All Collections About About Authorea FAQs Contact Us Quick Search anywhere Search for preprint articles, keywords, etc. Search Search ADVANCED SEARCH SCROLL This is a preprint and has not been peer reviewed. Data may be preliminary. 15 April 2025 V1 Latest version Share on Face-to-Face Type Giant Dimeric Donors Synergistically Improve the Stability and Efficiency of Organic Solar Cells Authors : Landi Zeng , Yongrui He , Ying Huang , Xucong Zhou , Jing Li , Kuan Li , Xiaoling Ma , … Show All … , Xin Zheng , Bin Wang , Fujun Zhang , Jingxia Wang 0000-0003-4780-4367 , lijun huo , yuchen yue , Bing Zheng 0009-0004-3841-7271 [email protected] , and Lei Jiang Show Fewer Authors Info & Affiliations https://doi.org/10.22541/au.174475647.79456101/v1 Published Journal of Materials Chemistry A Version of record Peer review timeline 201 views 133 downloads Contents Abstract Information & Authors Metrics & Citations View Options References Figures Tables Media Share Abstract With the development of organic solar cells (OSCs), maintaining the batch stability of photovoltaic donor materials and improving the device stability are becoming a new challenge. Given the successful application of giant oligomeric acceptors, increasing the molecular size while keeping precise molecular structure have been proven to be an effective method. However, the efficient giant oligomeric donors are still less due to a lack of design principles. Here, we innovatively designed and developed “face-to-face” type giant dimeric donors (GDDs), DZ-1 and DZ-2, by covalently tethering BTR-Cl monomer. Using the different rhodanine-based terminals significantly tuned their molecular interaction and thermal-driven assembly capability. Compare to DZ-1, DZ-2 had moderate molecular stacking and compatible miscibility in the blend film, thus realizing a higher PCE of 13.27%. Importantly, the GDDs with increasing molecular size not only improved the Tg, but also suppressed the molecular diffusion in blend films. Furthermore, the ternary OSCs based on PM6:DZ-2:L8-BO achieved an improved PCE of 18.89% and higher device stability, due to the establishment of 3D charge transport channel and suppression of the molecular diffusion. This study provides a new design strategy of giant molecule donors to develop high-performance and stable OSCs. 1. Introduction Organic solar cells (OSCs) have gained considerable attention due to their advantageous ability to print flexible, lightweight, and simple device processing [1-3] . The last several years have witnessed the rapid development of polymer donors with efficient charge transfer and tunable molecular structures, assisting power conversion efficiencies (PCEs) of OSCs over 19% [4-6] . With the in-depth study of polymer donor materials, finding that the polymers exhibit significant batch-to-batch differences owing to the molecular weight change and formation of structural defects caused by stepwise polymerization [7-10] . In comparison, small-molecule donors possess definite structure and good assembly to overcome the batch-to-batch difference [11-14] . But the thermodynamic relaxation of the mixed domains within the active layer of all-small-molecule solar cells (ASMSCs) is unavoidable, which lowers the probability of long-term stability [15-19] . To solve this problem, some studies have found that high glass transition temperature ( T g ) of small molecule is conducive to suppressing the demixing and crystallization of the small molecules with low diffusion coefficients in the blend, improving the long-term stability of OSCs [20-22] . Inspired by the available high T g of giant dimeric acceptor, the use of two small molecule donors, to develop giant dimeric donor (GDD) with definite molecular structure through an aromatic linker, offers a promising strategy to increase the long-term stability of OSCs. Some dimerized donors have been developed with targeted purposes. For example, He group designed and synthesized a dimerized small molecule donor, DSMD- β V, by connecting two asymmetric small molecule donors with the vinyl group [23] . Although the DSMD- β V helped ternary device achieve high PCE, it behaved poorly in binary devices. Wei group recently reported two GDDs by using two unique isomeric rhodanine-based linkers, realizing high PCE and good device stability [24] . The above research proves that giant molecule donors possess some potential to replace the batch-varied polymers, promoting the development of efficient and stable OSCs. However, these reported GDDs are prepared by adopting the same “head-to-head” tactics, restricting the innovation of giant molecule donors. Therefore, developing new preparation method about giant molecule donors is essential. Here, we proposed an alternative approach of covalently tethering small-molecule donors, designed and synthesized two new “face-to-face” type giant dimeric donors, DZ-1 and DZ-2 ( Figure 1a ). The different rhodanine-based terminals significantly impact their molecular interaction and thermal-driven assembly capability of DZ-1 and DZ-2. Meanwhile, the molecular interaction difference had obvious effects on the photophysical, electrochemical, and photovoltaic performance. To match the absorption and energy levels of GDDs, the Y6 was used as acceptor in the OSCs. Due to the excessively molecular aggregation, the DZ-1:Y6 blend films exhibited “slablike” microstructure and poor miscibility. In comparison, DZ-2 had moderate molecular stacking and compatible miscibility in the blend film. As a results, DZ-2 based OSCs exhibited a higher PCE of 13.27% than DZ-2 based device. Moreover, DZ-1 and DZ-2 based devices showed excellent photostability and thermostability owing to higher T g compared to small molecule donor BTR-Cl based device. Furthermore, the ternary OSCs based on PM6:DZ-2:L8-BO achieved an improved PCE of 18.89% and higher device stability, due to the establishment of 3D charge transport channel and suppression of the molecular diffusion. This study not only proposed a new design principles of giant molecule donors, but also provided research thought for developing high-performance and stable OSCs. 2. Results and discussion 2.1. Synthesis and Characterization Considering that the introduction of flexible linker in the GDDs can disturb the miscibility between donors and acceptors, thereby choosing the reported efficient small molecule donor BTR-Cl with strong crystallinity as monomer ( Figure S1 ) [25] . To further tune the molecular assembly, the rhodanine-based terminals is adjusted by using the hexyl and 2-ethyl hexyl chains. The synthetic routes of DZ-1 and DZ-2 were summarized in Scheme S1 of the supporting information (SI). With the flexible alkyl side chains to tether the monomer, it could bring excellent solubility in organic solvents including chloroform (CF), chlorobenzene (CB), etc. for device processing. Notably, the asymmetric terminals in the “face-to-face” type GDDs were inexistent. In consequence, the DZ-1 and DZ-2 exhibited simple reaction process and high yield of the Knoevenagel reaction, indicating that our work provided an effective method for dimeric donor synthesis. The UV-vis spectroscopy was used to investigate the optical properties for DZ-1 and DZ-2 in dilute chloroform solution and films. The detailed data was summarized in Table 1 . While in a dilute solution, the DZ-1 exhibited a raised aggregated peak compared to DZ-2 in 641 nm, indicating the DZ-1 had stronger molecular aggregation tendency ( Figure 1b ). Furthermore, the DZ-1 showed distinguishing maximum and shoulder absorption peaks located at ≈ 572 and 643 nm in films. The maximum and shoulder absorption peaks of DZ-2 displayed a distinct hypsochromatic shift ≈15 nm than those of DZ-1, which was ascribed to the restrained molecular stacking resulting from the increasement of steric hindrance by changing substituent of terminals. Due to the molecular stacking difference, the absorption onsets in films ( λ onset ) were 705 and 681 nm, correspondingly their optical bandgaps were 1.76 and 1.82 V for DZ-1 and DZ-2, respectively. The highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) of DZ-1 and DZ-2 were evaluated by using electrochemical cyclic voltammetry (CV) measurement ( Figure S2 ). As shown in Figure 1c , DZ-2 exhibited slightly deep LUMO and HOMO levels compared with DZ-1, due to the disturbed molecular planarity caused by rhodanine-based terminals. The measured HOMO/LUMO levels were -5.23/-3.52 eV and -5.27/-3.53 eV for DZ-1 and DZ-2, respectively. From the differential scanning calorimetry (DSC) measurements, DZ-1 and DZ-2 exhibited decreased melt points of 217.9 °C and 215.1 °C with decreased melting enthalpy (Δ H m ) of 4.20 J g -1 and 3.50 J g -1 compared to BTR-Cl (220.4 °C and 14.59 4.20 J g -1 ) ( Figure S3 ), which suggested that the tethered GDDs had reduced crystallinity. The low Δ H m of DZ-2 proved that the terminals could cause the crystal modification [26] . Figure 1. a) Head-to-head type and face-to-face type giant dimeric donors (DZ-1 and DZ-2). b) The normalized UV-vis absorption spectra of GDDs in solution and films. c) Energy level diagram of the related materials used in OSCs devices. d) The GIWAXS images corresponding IP and OOP line cuts of DZ-1 and DZ-2 neat films. To investigate the molecular packing and crystalline features of GDDs, the information of film morphology and orientation features for DZ-1 and DZ-2 were acquired by grazing incidence wide angle X-ray scattering (GIWAXS) measurement ( Figure S4 ). As shown in Figure 1d . the DZ-1and DZ-2 neat films exhibited preferable edge-on molecular orientation and distinct lateral stacking (100) diffraction peaks at 0.33 and 0.35 Å -1 in the OOP direction, and the corresponding π - π stacking distances were 9.52 and 8.97 Å. Importantly, DZ-2 exhibited weaker 100 diffraction peaks compared to DZ-1, and the crystalline coherence length (CCL) could be calculated in the OOP direction according to the Scherrer equation. The results showed that the CCLs of DZ-1 and DZ-2 neat films were 6.96 and 2.39 Å, respectively, which indicated that the crystallinity of DZ-2 was weaker than DZ-1 due to the enhancement of steric hindrance caused by rhodanine-based terminals. To explain the molecular packing difference, the spatial configurations are studied for DZ-1 and DZ-2. The optimized conformations of trimers were exhibited by using density functional theory (DFT) at the B3LYP/6-31G* (d, p) level by the Gaussian 16 software. For simplification, the 2-ethylhexyl and a portion of hexyl chains were replaced by methyl groups. The result of dihedral angles was shown in Table S1 . As shown in Figure S5 , DZ-1 and DZ-2 had minor intramolecular torsion of monomer, which was beneficial to molecular packing. In addition, the dihedral angles between terminal and thiophene of DZ-2 were slightly larger than those of DZ-1, due to the larger steric hindrance of 2-ethylhexyl compared to hexyl. Therefore, the DZ-2 exhibited relatively weak molecular packing, which matched the GIWAXS result. Table 1. The summary of optical and electronic properties for the GDDs. solution film DZ-1 536 574 705 1.76 -5.23 -3.52 1.71 226/240 217.9 4.20 DZ-2 526 558 681 1.82 -5.27 -3.53 1.74 243 215.1 3.150 a) Absorption edge of the polymer films; b) Calculated from the absorption edge of the polymer films: E g opt = 1240/λ edge ; c) E g ec = E LUMO − E HOMO . 2.2. Photovoltaic Properties To evaluate the photovoltaic performance of DZ-1 and DZ-2, the OSCs were fabricated with device configuration of indium tin oxide (ITO)/poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS)/GDDs:Y6/PNDIT-F3N/Ag. The detailed devices optimization process including the various D/A ratio, annealing temperature, and the additive content are summarized in Figure S6 and Table S2-S4 . The J - V curves of the optimized devices based on GDDs:Y6 are provided in Figure 2a , and the corresponding parameters are listed in Table 2 . The device based on DZ-1:Y6 could realize a low PCE of 4.97%, with V OC of 0.834 V, J SC of 15.99 mA cm -2 , and FF of 37.24%. For DZ-2, the optimal device showed a higher PCE of 13.27%, with V OC of 0.844 V, J SC of 23.93 mA cm -2 , and FF of 65.69%. As a contrast, the OSCs based on BTR-Cl:Y6 were prepared, and exhibited a PCE of 13.83%, with V OC of 0.862 V, J SC of 24.47 mA cm -2 , and FF of 65.58% ( Figure S6 ). The device efficiency was matched with previous report [27] . Although the photovoltaic efficiency of the GDDs based device was slightly lower than all-small-molecule OSCs, the GDDs based device had more advantages in terms of device stability, and the corresponding content was discussed in the following section. In Figure 2b , the external quantum efficiency (EQE) spectra of the optimal devices for DZ-1 and DZ-2 showed strong photoresponse in the wavelength range of ≈ 400-880 nm. In comparison with the DZ-1 based device, the device based on DZ-2:Y6 exhibited observably larger photoresponse area, and thus the more efficient photon-harvesting generated the higher J SC value. The charge mobility can significantly influence the J SC and FF, thus measuring the charge carrier mobilities of the neat and blend films for two GDDs by the space-charge-limited current (SCLC) method ( Figure S8 ). The hole and electron mobility data was summarize in Table S5 . Thereinto, the hole motility ( µ h ) were 9.6 × 10 -5 and 8.2 × 10 -4 cm 2 V -1 s -1 for DZ-1 and DZ-2, respectively. For the blend films, the DZ-1:Y6 and DZ-2:Y6 systems had µ h and electron ( µ e ) mobilities of 2.2 × 10 -5 /8.7 × 10 -5 cm 2 V -1 s -1 and 6.4 × 10 -4 /4.1 × 10 -4 cm 2 V -1 s -1 , respectively. The improved charge carrier mobilities in the DZ-2:Y6 system was attributed to the appropriate miscibility between donor and acceptor, which would be discussed below. In addition, the ratios of µ h / µ e were obtained to be 0.25 and 1.56 for DZ-1:Y6 and DZ-2:Y6 systems, respectively, and the balanced hole/electron mobilities ratio in the DZ-2 based blend films could boost the increased FF. Table 2. Summary of device parameters of GDDs:Y6-based devices based on optimized conditions under the illumination of AM 1.5 G, 100 mW cm –2 . DZ-1:Y6 a) 0.834 (± 0.005) 15.99 (± 0.3) 15.41 (± 0.25) 37.24 (± 0.05) 4.97 (± 0.25) DZ-2:Y6 a) 0.844 (± 0.005) 23.93 (± 0.3) 23.40 (± 0.25) 65.69 (± 0.05) 13.27 (± 0.3) a) Fabricated with SVA and annealing at 110 °C; b) Integrated from EQE values; c) All average values were calculated from ten devices. The exciton dissociation and charge recombination of the OSCs was further investigated by the relationship of photocurrent density ( J ph ) versus the effective voltage ( V eff ), as well as the dependency of the J SC / V OC and light intensity ( P light ) were conducted. Generally, the J ph is given as J ph = J L - J D , in which J L and J D represent the current density under illumination and dark, respectively. V eff equals the difference between V and V 0 , where V is the applied voltage and V 0 is the voltage when J ph = 0. The J ph reaches saturation ( J sat ) can be defined as V eff ≥ 2 V [28] . Consequently, the probability of charge dissociation ( 𝜂 diss ) and collection ( 𝜂 coll ) of photocurrent carriers can be obtained via the ratio of J ph / J sat and J max /J sat , respectively. As shown in Figure 2c , the values of 𝜂 diss and 𝜂 coll for DZ-1:Y6 and DZ-2:Y6 systems were 82.33%/75.86% and 93.27%/86.38%, respectively. This result suggested that the device based on DZ-2:Y6 system had more efficient exciton dissociation and charge extraction in comparison with DZ-1 based device. Additionally, the dependency between J SC and P light was investigated by the power law J SC ∝ P light S to study the charge recombination mechanism [29] . In Fig. 2d , the devices based on DZ-1:Y6 and DZ-2:Y6 exhibited the the S values of 86.7% and 92.4%, respectively. The S value of DZ-2 based device was closer to 1, which indicated the less charge-recombination for OSCs based on DZ-2:Y6. To investigate the mode of charge recombination, the relationship of V OC and P light was study by fitting the slope of n(kBT)/q under open-circuit condition. Thereinto, kB is Boltzmann’s constant, T is temperature, and q is the elementary charge. When the n is closer to 1 or 2, the charge-recombination is bimolecular recombination or monomolecular recombination as dominance, respectively [30] . As shown in Figure 2e , the DZ-1 and DZ-2 based devices exhibited the slopes of fitted data of 1.67 and 1.22 kBT q -1 , which suggested that DZ-1 and DZ-2 based devices were monomolecular and bimolecular recombination as dominance, respectively. Moreover, the charge extraction time were determined from the transient photocurrent (TPC) measurements. In Fig. 2f , the charge extraction time of the device based on DZ-2:Y6 was 0.57 µs, which was lower than that of the device based on DZ-1:Y6 (1.34 µs). This result confirmed the efficient charge extraction in DZ-2:Y6 system by this fastest transient photocurrent lifetime. Figure 2. a) J-V curves of the best OSCs based on GDDs:Y6 under the illumination of AM1.5G, 100 mW cm -2 . b) EQE curves of the corresponding OSCs. c) J ph versus V eff of the OSCs based on GDDs:Y6. d) Light intensity dependence of J SC values of the corresponding OSCs. e) Light intensity dependence of V OC values of the corresponding OSCs. f) TPC properties of devices The femtosecond transient absorption spectroscopy (fs-TA) was selected to gain deep insight into the dynamics of the excitons generation and dissociation in the GDD systems [31] . The pump laser was set at 800 nm for selectively exciting Y6 acceptor, and spectra recorded at different decay time are shown in Figure 3 . And the corresponding TA map was exhibited in Figure S9. There is an evident ground state bleach (GSB) recorded at 810 nm, which indicated the formation of the excited state for Y6. Observingly, the broad excited state absorption (ESA) of acceptor was evident for DZ-2:Y6 system at 580 nm, but DZ-1:Y6 system was unclear. The GSB matching the absorption of DZ-1:Y6 and DZ-2:Y6 systems was also observed at 645 and 628 nm, respectively, which suggested that the ultrafast hole transfer from Y6 to GDDs at the D/A interface, and then recombination to ground state. In addition, although the ESA CT was also observed at 669 and 674 nm for DZ-1:Y6 and DZ-2:Y6 systems, the ESA CT based on the DZ-1:Y6 system was low-fluctuation, proving that the charge transfer was low efficiency between donor and acceptor [32] . Furthermore, the kinetic trace of the GSB for donors was compared, and the fitting of the time-resolved spectra was collected in Figure 3b . The DZ-2:Y6 system gives the shortest charge transfer lifetime of 12 ps, which exhibited the faster CT process than DZ-1:Y6 system. Figure 3. a) The fs-TA spectra recorded ranging from 60 fs to 1.5 ns for DZ-1:Y6. b) The fs-TA spectra recorded ranging from 60 fs to 1.5 ns for DZ-2:Y6. c) The fitting curves at GSB D for DZ:Y6 and DZ-2:Y6. To explore the reason of charge transfer difference for DZ-1:Y6 and DZ-2:Y6 systems, the microtopography of GDD blend films was study by the GIWAXS and atomic force microscope (AFM) measurement. As shown in Figure 4a , all blend films showed obvious edge-on molecular orientation in the OOP direction, and the corresponding diffraction peaks are located at 0.33 Å -1 (d-spacing: 19.02 Å) and 0.31 Å -1 (d-spacing: 20.26 Å) for DZ-1:Y6 and DZ-2:Y6. It was worth mentioning that the DZ-1:Y6 blend film had stronger 100 diffraction peak than DZ-2:Y6 system in the OOP direction, indicated the increased the molecular packing. Interestingly, the 010 diffraction peak of DZ-2:Y6 system was stronger than DZ-1:Y6 blend film. Therefore, the DZ-2:Y6 system tended to mix molecular stacking orientation. On the other hand, the CCLs of DZ-1:Y6 and DZ-2:Y6 systems were calculated in the OOP direction, which were 12.54 and 6.60 Å, respectively. Judging from the CCL results, the DZ-1:Y6 system existed exceedingly large crystallinity, thereby causing the difficulty in charge extraction. As shown in Figure 4b , the DZ-1 neat film exhibited a higher root-mean-square (RMS) roughness values of 0.66 nm compared to DZ-2 (0.37 nm). Under the optimized device fabrication conditions, the DZ-1:Y6 blend film showed sharply increased phase separation (RMS = 6.21 nm), which was worse microstructure compared to DZ-2:Y6 blend film (RMS = 0.62 nm). This result proved that the terrible microtopography of DZ-1:Y6 active layer caused the inferior charge transfer, influencing the improvement of photovoltaic performance. Figure 4. a) The GIWAXS images of GDDs: Y6, and the corresponding IP and OOP line cuts. b) AFM height images of GDDs neat films and GDDs: Y6 blends with optimal condition. Because the miscibility between the donor and acceptor play an important role for tuning the intermolecular charge transfer, the contact angles (CA) of two solvents (water and glycerol) on the DZ-1, DZ-2 and Y6 neat films were measured to calculate the interfacial tensions ( γ ) between the donor and acceptor by the Wu model [33] . In Figure S10 , the water/glycerol contact angles were 96.1°/85.4°, 94.8°/83.2°, and 97.3°/81.0° for DZ-1, DZ-2, and Y6, and corresponding γ values were 19.649, 21.381, and 26.956, respectively. The detailed data was summarized in Table S2. Then the Flory-Huggins interaction parameter was calculated by the equation of\(\chi\propto{(\sqrt{\gamma_{A}}-\sqrt{\gamma_{B}})}^{2}\), to evaluate the miscibility between donor and acceptor [34] . The calculated χ values were 0.577 and 0.323 for DZ-1:Y6 and DZ-2:Y6 systems, which indicated that the DZ-2 had better miscibility with Y6 than DZ-1, achieving the efficient intermolecular charge transfer. 2.3. The Effect of Dimerization on Device Stability The T g of small molecule is a critical thermal property of organic photovoltaic materials to maintain the morphological stability. Generally, the T g values of small molecule can affect their diffusion and crystallization in the active layer, thus influencing the device stability [35] . Due to no glass transition signals of GDDs in the DSC, the T g values of GDDs were estimated by the absorption spectroscopy following the previous research method [36] . To comprehend this T g difference between small molecule donor and giant dimeric donor, the T g of BTR-Cl was also estimated, and the initial data was showed in Figure S11 . As shown in Figure 5a-c , the DZ-1 and DZ-2 had higher T g values compared to BTR-Cl, which was conducive to suppressing the diffusion-enabled demixing in the active layer. Thereinto, DZ-2 exhibited highest T g values of 91.9 ℃, and this result was matched with the crystallization temperature ( T c ) ( Figure 5d ) [37] . To verify the device stability for OSCs including GDDs, the photostability and thermostability were tested in the N 2 atmosphere, respectively. As shown in Figure 5e , the photostability of devices was measured under white light, and the DZ-1 and DZ-2 based OSCs suffered from alleviated burn-in, exhibited better photostability in comparison with that of BTR-Cl based OSCs. Thereinto, the devices based on GDDs:Y6 maintained an initial efficiency over 75% after more than 160 h, which was much stronger than the small molecule based device. Furthermore, benefiting from the high T g of GDDs, the GDD-based devices showed much slower decay trend at 100 °C in the nitrogen atmosphere ( Figure 5f ). It was worth noting that the T80 (retained 80% of the initial efficiency) of DZ-1 and DZ-2 based devices were about 350 and 480 h, which was higher than the 130 h of BTR-Cl based OSCs, indicating the better device thermostability for GDDs. Besides, the AFM height images based on GDDs:Y6 blend films and BTR-Cl:Y6 blend films were tested after 96 hours of heating in the nitrogen atmosphere. As shown in Figure S12 , compared to the optimized blend films based on GDDs:Y6, the aged blend films of GDDs showed minor change of RMS, indicating the stability of microstructure after heating. For the active layer based on BTR-Cl:Y6, the RMS value was 1.27 nm under the optimized condition. However, the RMS value of BTR-Cl based blend film dropped from 1.27 to 0.693 nm, suggesting the obvious change of microstructure for active layer. This result reasonably explains the tethered GDDs limited the available molecular motion to reduce their diffusivity in the blend film, which was beneficial to maintain morphological stability, thus achieving the excellent device stability than all-small-molecule OSCs. Figure 5. a)-c) T g of BTR-Cl, DZ-1, and DZ-2, as well as the slope of deviation metric over temperature above T g . d) T c of BTR-Cl, DZ-1, and DZ-2. e) photostability test of the GDDs:Y6 and BTR-Cl: Y6 based devices under the illumination of a 100 mW cm -2 white LED. f) Normalized PCEs of the GDDs: Y6 and BTR-Cl: Y6 based devices under long-term annealing at 100 °C in nitrogen-filled glovebox. 2.4. The Application of GDDs as Third Components in the Ternary OSCs Considering the excellent features of GDDs, we further applied GDDs as third component to the ternary OSCs, and the detailed fabrication processes were summarized in the supporting information. The current density-voltage ( J-V ) curves of the optimized ternary devices were exhibited in Figure 6a , and corresponding detailed device parameters were listed in Table 3 . The binary PM6:L8-BO device exhibited a PCE of 17.53% with a J SC of 25.21 mA cm -2 , a V OC of 0.898 V, and an FF of 77.45%. With the introduction of DZ-1 and DZ-2 as third components, the ternary devices exhibited improved PCEs of 17.75 and 18.89%, respectively. In comparison, these ternary devices had a higher J SC than the binary device, and the proportions of increase in J SC are 1.86 and 6.55% for DZ-1 and DZ-2 as third components, respectively. In view of this, the corresponding external quantum efficiency (EQE) spectra are shown in Figure S13 . All the ternary OSCs showed strong photoresponse than binary OSCs in the wavelength range of ≈ 400-850 nm, consequently, the ternary devices displayed the highest J SC values. Table 3. Summary of device parameters of PM6:GDDs:L8-BO based devices based on optimized conditions under the illumination of AM 1.5 G, 100 mW cm -2 . PM6:L8-BO a) 0.898 (± 0.005) 25.21 (± 0.3) 24.20 (± 0.25) 77.45 (± 0.05) 17.53 (± 0.3) PM6:DZ-1:L8-BO a) 0.893 (± 0.005) 25.68 (± 0.3) 24.71 (± 0.25) 77.42 (± 0.05) 17.75 (± 0.3) PM6:DZ-2:L8-BO a) 0.894 (± 0.005) 26.86 (± 0.3) 25.62 (± 0.25) 78.65 (± 0.05) 18.89 (± 0.3) a) Fabricated with 0.25% DIO and annealing at 85 °C; b) Integrated from EQE values; c) All average values were calculated from ten devices. To ascertain the reason of higher J SC s for ternary devices, the charge transport ability was evaluated from horizontal and vertical directions. For horizontal charge transport, DZ-1 and DZ-2 were fabricated on the SiO 2 /Si wafer, and the top-contact (TC) OFETs devices were constructed after symmetric Au electrodes were evaporated onto the films with the assistance of shadow masks. As shown in Figure 6b and 6c , the OFET device of DZ-1 showed a higher carrier mobility of 1.9 × 10 -1 cm 2 V -1 s -1 comparing to DZ-2 (4.4 × 10 -2 cm 2 V -1 s -1 ) under the same V G . The improved performance of the OFETs was attributed to the enhanced edge-on aggregation for DZ-1, which facilitated the lateral charge transfer. Afterwards, the vertical charge carrier mobilities of the binary and ternary devices were measured by the SCLC method ( Figure S14 ). The corresponding parameters were summarized in Figure 6d and Table S6 . The binary device based on PM6:L8-BO had μ h of 4.65 × 10 -4 cm 2 V -1 s -1 and μ e of 4.12 × 10 cm 2 V -1 s -1 . With the addition of GDDs, the charge motilities of ternary devices had a corresponding increase. In particular, the μ h and μ e of ternary blend film based on PM6:DZ-2:L8-BO reached 6.86 × 10 -4 cm 2 V -1 s -1 and μ e of 6.42 × 10 cm 2 V -1 s -1 , respectively. Moreover, the ratio of μ h / μ e was only 1.07 for DZ-2 based ternary blend film. Therefore, these results interpreted that the ternary OSCs based on PM6:DZ-2:L8-BO systems had higher J SC and FF. Besides, the photostability and thermostability of binary and ternary devices was investigated in the N 2 atmosphere, respectively. As shown in Figure 6e and 6f , the ternary devices based on PM6:DZ-1:L8-BO and PM6:DZ-2:L8-BO systems maintained better photostability and thermostability than those of binary devices. Thereinto, the DZ-2-based ternary devices presented the best performance in this research, which maintained more than 80% of the initial performance over 390 h for photostability of devices, and more than 80% over 500 h for thermostability of devices. Figure 6. a) J-V curves of the best binary and ternary OSCs based under the illumination of AM1.5G, 100 mW cm -2 . Charge transfer characteristic of OFET based on b) DZ-1 and c) DZ-2. d) Charge mobilities of the binary and ternary devices by SCLC method. e) photostability test of the binary and ternary OSCs under the illumination of a 100 mW cm -2 white LED. f) Normalized PCEs of the binary and ternary OSCs under long-term annealing at 100 °C in nitrogen-filled glovebox. The study of details including molecular stacking, and microstructure of active layers helped us understand the causes of high PCE and favourable device stability. As illustrated in Figure 7a , the binary and ternary systems showed pronounced scattering peaks (010) in the OOP direction by the GIWAXS measurement, but the intensity of 010 peaks were different. On the one hand, the DZ-1-based and DZ-2-based ternary films had stronger and weaker 010 peaks than that of binary films, respectively, which attributed to the crystallinity difference. The corresponding diffraction peaks were located at 1.748 and 1.757 Å -1 (d-spacing: 3.593 and 3.574 nm) in the DZ-1-based and DZ-2-based ternary films, which was a little more than the binary films (3.568 nm). Meanwhile, the CCLs of the binary and ternary films were 4.83, 12.2, and 3.61 Å in the OOP direction, respectively. On the other hand, the DZ-2-based ternary films exhibited significantly enhanced 100 scattering peaks in the IP direction, and CCLs of the binary and ternary films were 30.37, 54.35, and 24.15 Å in the IP direction, respectively. These results suggested that the introduction of edge-on orientation of DZ-1 and DZ-2 was contributed to forming the mixed face-on and edge-on orientation, facilitating the establishment of 3D charge pathways in the ternary films. However, the ternary films based on PM6:DZ-1:L8-BO had greater crystalline change than binary films, resulting in the difficult synchronization for horizontal and vertical charge transfer, thereby sparingly improving J SC . For DZ-2-based ternary films, the crystalline was less change as opposed to binary films, thus further improving the charge transport capacity of ternary OSCs by the 3D charge pathways [38-40] . Afterwards, the microstructure of the active layers of binary and ternary films were investigated by the AFM. As shown in Figure S15 , the introduction of DZ-1 and DZ-2 enhanced and reduced the RMS values to some extent, due to the difference of crystallinity in the ternary films, respectively. After 96 hours of heating in the nitrogen atmosphere, the aged binary films showed great change of RMS, and aged ternary systems had minor change of RMS. Especially, the RMS values of ternary based on PM6:DZ-2:L8-BO dropped from 1.06 to 0.94 nm, and the minimal morphological change among three systems contributed to achieving the excellent device stability. The influencing mechanism of GDDs on the ternary OSCs can be well described in Figure 7b . The stable stacking of GDDs help improve the stability of microstructure of active layers originated from the high T g of GDDs, realizing the good device stability. But the crystallinity difference of GDDs can influence the establishment of 3D charge pathways in the ternary films, showing different abilities of hole bypassing acceptor domains and refraining from the annihilation of holes in the acceptor regions. Figure 7. a) The GIWAXS images of binary and ternary blend films, as well as corresponding IP and OOP line cuts. b)Schematic diagram of the GDDs influencing the PCE and device stability ternary OSCs. 3. Conclusion In conclusion, to enhance batch stability of organic photovoltaic material while improving device stability, here we innovatively designed and developed “face-to-face” type giant dimeric donors by covalently tethering BTR-Cl monomer. In the molecular fragment, the BTR-Cl monomers were linked to a benzyl core with a flexible spacer, and the different rhodanine-based terminals significantly tuned their molecular interaction and thermal-driven assembly capability of DZ-1 and DZ-2. Due to the excessively molecular aggregation, the DZ-1 exhibited “slablike” microstructure and poor miscibility with Y6 acceptor in the blend films. In comparison, DZ-2 had moderate molecular stacking and compatible miscibility in the blend film. As a results, DZ-2 based OSCs exhibited a higher PCE of 13.27% than DZ-1 based device. Importantly, the GDDs with increasing molecular size suppressed the molecular diffusion in blend films. Meanwhile, the T g of GDDs was improved than BTR-Cl monomer, thereby realizing dramatically increased photostability and thermostability in devices. Furthermore, the ternary OSCs based on PM6:DZ-2:L8-BO achieved an improved PCE of 18.89% and higher device stability, due to the establishment of 3D charge transport channel and suppression of the molecular diffusion. Considering that the face-to-face type giant dimeric donors can be further optimized via molecular engineering (such as tuning small molecule monomer, linker core, and terminals), this study provides a new design strategy of giant molecule donors to develop high-performance and stable OSCs. Conflicts of interest The authors declare that they have no conflict of interest. Acknowledgements L. Zeng and Y. He contributed equally to this work. The research was supported by the Scientific Research Project of Shandong Second Medical University, the Shandong Province Natural Science Foundation (ZR2024QB300, ZR2022QB246), Special Funds for Taishan Scholar Foundation of Shandong Province (tsqn202211366). The grazing incidence wide-angle X-ray scattering (GIWAXS) were collected on the NFPS BL17B1 of Shanghai Synchrotron Radiation Facility (SSRF), and were provided technical support by “Ceshigo Research Service, www.ceshigo.com”. References [1] C. Liu, Y. Fu, J. Zhou, L. Wang, C. Guo, J. Cheng, W. Sun, C. Chen, J. Zhou, D. Liu, W. Li, T. Wang, Alkoxythiophene‐Directed Fibrillization of Polymer Donor for Efficient Organic Solar Cells, Adv. Mater. 2023 , 36 , 2308608. [2] S. Liu, J. Wang, S. Wen, F. Bi, Q. Zhu, C. Yang, C. Yang, J. Chu, X. Bao, Efficient Dual Mechanisms Boost the Efficiency of Ternary Solar Cells with Two Compatible Polymer Donors to Exceed 19%, Adv. Mater. 2024 , 36 , 2312959. [3] H. Chen, R. Zhang, X. Chen, G. 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Keywords giant dimeric donors organic solar cells photostability thermostability Authors Affiliations Landi Zeng Shandong Second Medical University View all articles by this author Yongrui He Shandong Second Medical University View all articles by this author Ying Huang Shandong Second Medical University View all articles by this author Xucong Zhou Shandong Second Medical University View all articles by this author Jing Li Technical Institute of Physics and Chemistry Chinese Academy of Sciences View all articles by this author Kuan Li Shandong Second Medical University View all articles by this author Xiaoling Ma Beijing Jiaotong University View all articles by this author Xin Zheng shandong industrial technician college View all articles by this author Bin Wang Shandong Second Medical University View all articles by this author Fujun Zhang Beijing Jiaotong University View all articles by this author Jingxia Wang 0000-0003-4780-4367 Technical Institute of Physics and Chemistry Chinese Academy of Sciences View all articles by this author lijun huo Beihang University View all articles by this author yuchen yue Technical Institute of Physics and Chemistry Chinese Academy of Sciences View all articles by this author Bing Zheng 0009-0004-3841-7271 [email protected] Shandong Second Medical University View all articles by this author Lei Jiang Beihang University View all articles by this author Metrics & Citations Metrics Article Usage 201 views 133 downloads .FvxKWukQNSOunydq8rnd { width: 100px; } Citations Download citation Landi Zeng, Yongrui He, Ying Huang, et al. Face-to-Face Type Giant Dimeric Donors Synergistically Improve the Stability and Efficiency of Organic Solar Cells. Authorea . 15 April 2025. DOI: https://doi.org/10.22541/au.174475647.79456101/v1 If you have the appropriate software installed, you can download article citation data to the citation manager of your choice. Simply select your manager software from the list below and click Download. For more information or tips please see 'Downloading to a citation manager' in the Help menu . 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