> ## Content Index > Fetch the complete content index at: https://research-pop.com/llms.txt > Use this file to discover other available public pages before exploring further. # Beijing University of Chemical Technology-led team directs molecular assembly for efficient organic solar cells - URL: https://research-pop.com/beijing-university-of-chemical-technology-led-team-directs-molecular-assembly-for-efficient-organic-solar-cells/ - Published: 2026-10-21T08:23:23.000Z - Updated: 2026-10-21T08:23:23.000Z - Author: ResearchPOP ![](https://storage.ghost.io/c/7c/5e/7c5e0911-739b-4a35-94eb-3e810bf78ba7/content/images/2026/10/Screenshot-2026-10-21-at-09.41.54.png) Source: [https://www.nature.com/articles/s41560-026-02148-w](https://www.nature.com/articles/s41560-026-02148-w?ref=research-pop.com) [Directed assembly of cathode interlayers enables efficient binary organic solar cells - Nature EnergyCathode interlayers play a pivotal role in improving the performance of organic solar cells. Yao, Zhang, Zhang, Wang et al. show a stepwise solvent treatment to achieve a vertically aligned cathode interlayer, enabling a certified efficiency of 20.65% in binary organic solar cells.![](https://storage.ghost.io/c/7c/5e/7c5e0911-739b-4a35-94eb-3e810bf78ba7/content/images/icon/favicon-48x48-b52890008c-dad8d869-8e4c-441f-a492-5503f913ed90.png)Nature Publishing Group UKJia Yao![](https://storage.ghost.io/c/7c/5e/7c5e0911-739b-4a35-94eb-3e810bf78ba7/content/images/thumbnail/41560_2026_2148_Fig1_HTML-8db8c4e0-8207-408e-9cb8-c4389c90e4d6.png)](https://www.nature.com/articles/s41560-026-02148-w?ref=research-pop.com) ## At a glance The efficiency of an organic solar cell depends on both its light-absorbing materials and the interfaces that charges cross before reaching the electrodes. A Beijing University of Chemical Technology-led collaboration improves that interface by controlling how molecules assemble in the cathode interlayer. The researchers treat the active layer with methanol before depositing a perylene diimide-based interlayer, PDISNN, from TFE. This sequence produces a more perpendicular molecular orientation. Spectroscopy, simulations and electrical measurements connect the arrangement with a stronger interfacial dipole, more favourable energy alignment and lower resistance. A D18:L8-BO binary organic solar cell reaches a champion power-conversion efficiency of 20.72%, with an independently certified value of 20.65%. A 1 cm² device achieves 19.20%, while stability testing gives a T₈₀ lifetime of 984 hours, compared with 330 hours for the comparison device. ## Background Organic solar cells use carbon-based semiconductors to absorb light and generate electrical charges. In a binary device, the active layer contains two principal components: an electron donor and an electron acceptor. Their interfaces help separate photoexcited states into electrons and holes, which must then travel towards opposite electrodes. The layers connecting the active material to those electrodes influence how efficiently charges are collected. At the electron-collecting contact, a cathode interlayer can adjust energy alignment, support electron transport and reduce losses. Even a thin interlayer can therefore affect the current, voltage and fill factor of the complete device. Molecular orientation is one way to tune that contact. A molecular dipole arises from an uneven distribution of charge. Its contribution to the potential across an interface depends on how it is aligned: molecules with similar dipoles can produce different interfacial effects if they lie flat, tilt or stand more upright. Assembly is also sensitive to processing. Solvents influence wetting, molecular interactions and the condition of the underlying surface. For amphiphilic molecules, whose different regions interact differently with their surroundings, the deposition sequence can help determine the final arrangement. This study connects those processing choices with device physics. The researchers compare three PDI-based interlayers—PDINN, PDISNN and PDI2SNN—and then investigate whether a methanol pretreatment can direct their assembly on the active layer. ## Research question Can changing the order of solvent treatment and interlayer deposition produce a molecular orientation that improves electron extraction? The researchers examine whether structural measurements can connect the deposition sequence to changes in interfacial dipole, work function, built-in potential and resistance. They also test whether the strategy transfers across several active-layer and interlayer combinations, and whether its benefits persist in larger-area and stability experiments. ## Inside the study ### Selecting an interlayer with suitable packing and electronic properties ![](https://storage.ghost.io/c/7c/5e/7c5e0911-739b-4a35-94eb-3e810bf78ba7/content/images/2026/10/Screenshot-2026-10-21-at-09.42.03.png) **Figure 1 introduces the three interlayer molecules and compares their optical, electronic and packing characteristics.** This establishes why molecular selection and assembly control need to be considered together. Among the tested materials, PDISNN has the shortest reported π–π stacking distance, 3.47 Å, and the largest coherence length, 50.41 Å. Its relative crystallinity is 1.00\. Together, these measurements indicate comparatively close and extended ordered packing within the series. PDISNN also has a conductivity of 5.79 × 10⁻⁴ S cm⁻¹, relevant to its role as a charge-transporting contact layer. Its calculated molecular dipole is 1.08 D, compared with 0.33 D for PDI2SNN. A larger molecular dipole does not automatically produce a stronger useful interfacial effect. Its orientation matters as well. The material comparison therefore establishes the starting point for the study’s central question: how to arrange the selected molecules at the electrode interface. ### Changing the order of deposition ![](https://storage.ghost.io/c/7c/5e/7c5e0911-739b-4a35-94eb-3e810bf78ba7/content/images/2026/10/Screenshot-2026-10-21-at-09.42.13.png) **Figure 2 compares three processing routes and their effects on wetting, assembly and solar-cell performance.** Method I deposits the interlayer directly from TFE. Method II follows that deposition with a methanol rinse. Method III reverses the sequence: the active layer is treated with methanol first, and the interlayer is then deposited from TFE. The third route changes the surface that the incoming interlayer molecules encounter. The authors describe it as methanol-templated assembly, linking the pretreatment to improved wetting and a different molecular arrangement. In a PM6:BTP-eC9 device using PDISNN, Method III gives a power-conversion efficiency of 18.25%, compared with approximately 14.6–15.0% for the direct-deposition comparisons. The Method III device has an open-circuit voltage of 0.85 V, a short-circuit current density of 27.23 mA cm⁻² and a fill factor of 78.40%. These results show that the sequence of processing steps can substantially affect performance even when the principal active-layer and interlayer materials remain the same. ### Connecting molecular orientation with charge extraction ![](https://storage.ghost.io/c/7c/5e/7c5e0911-739b-4a35-94eb-3e810bf78ba7/content/images/2026/10/Screenshot-2026-10-21-at-09.42.36.png) **Figure 3 brings together the structural and electrical evidence for the proposed assembly mechanism.** Sum-frequency generation spectroscopy, molecular dynamics and near-edge X-ray absorption fine structure measurements provide complementary views of the interlayer orientation. The reported average orientation angle increases from 74.54° for Method I to 78.38° for Method II and 85.01° for Method III. Under the authors’ angle convention, the methanol-pretreated route produces the arrangement closest to perpendicular. Surface-potential measurements connect this change with the local energetic environment. Method III gives a surface-potential difference of 233 mV and shifts the active-layer work function from 4.26 to 4.17 eV. The device measurements show a corresponding change in charge collection. The built-in potential rises from approximately 0.65 to 0.82 V, while series resistance falls from 158.6 to 29.6 Ω. Taken together, the results support the authors’ proposed sequence: methanol pretreatment changes assembly, the more upright molecular arrangement strengthens the effective interfacial dipole, and the resulting energy alignment facilitates charge extraction. The mechanism is supported by several measurements beyond the final efficiency comparison. ### Testing the strategy across materials, area and operating time ![](https://storage.ghost.io/c/7c/5e/7c5e0911-739b-4a35-94eb-3e810bf78ba7/content/images/2026/10/Screenshot-2026-10-21-at-09.42.43.png) **Figure 4 examines how broadly the assembly strategy works.** The researchers extend the tests to PM6:PY-IT, PM6:L8-BO and D18:L8-BO active layers, as well as several interlayers. The champion D18:L8-BO device reaches 20.72% power-conversion efficiency. Independent certification gives 20.65% efficiency with an 82.7% fill factor. The fill factor describes how effectively the device’s current–voltage response translates its voltage and current into usable maximum power. A device with an area of 1 cm² achieves 19.20% efficiency. This extends the demonstration to a larger laboratory cell and provides a separate measure of performance beyond the champion device. Stability testing gives a T₈₀ lifetime of 984 hours, compared with 330 hours for the comparison device. T₈₀ is the time taken for performance to fall to 80% of its initial value under the specified test conditions. Within the tested configurations, the processing strategy is therefore associated with both higher initial efficiency and longer performance retention. Establishing how these results translate to modules will require further assessment of coating uniformity, operating conditions and manufacturing processes. ## Takeaways and outlook The study shows how a solvent-treatment sequence can control the molecular arrangement of a cathode interlayer. Treating the active layer with methanol before depositing PDISNN produces a more perpendicular orientation, with accompanying changes in interfacial potential, energy alignment and resistance. Its evidence connects several levels of device design: molecular properties guide interlayer selection, processing directs assembly, spectroscopy examines orientation, and electrical measurements link the interface to solar-cell performance. The certified efficiency, tests across multiple material combinations, 1 cm² device and operational-retention measurements broaden the experimental case. Further work can establish whether the same orientation control remains effective over larger areas and under manufacturing-relevant coating and drying conditions. ## About the researchers Jia Yao, Rui Zhang, Ming Zhang and Tonghui Wang contributed equally. Jia Yao is affiliated with Beijing University of Chemical Technology and the Institute of Chemistry, Chinese Academy of Sciences. Rui Zhang is affiliated with Soochow University and Linköping University, Ming Zhang with Beijing University of Chemical Technology, and Tonghui Wang with Jilin University. The corresponding authors are Zhen Zhang of the Institute of Chemistry, Chinese Academy of Sciences; Feng Gao of Linköping University; and Zhi-Guo Zhang of Beijing University of Chemical Technology. Nakul Jain is affiliated with Linköping University. Yushan Liu, Caihe Liu, Xiaohan Liu and Yongfang Li are affiliated with the Institute of Chemistry, Chinese Academy of Sciences. Shixin Meng, Aonan Song, Qingyuan Wang and Qi Chen are affiliated with Beijing University of Chemical Technology. ## Original research Jia Yao; Rui Zhang; Ming Zhang; Tonghui Wang; Nakul Jain; Yushan Liu; Caihe Liu; Xiaohan Liu; Zhen Zhang; Shixin Meng; Aonan Song; Qingyuan Wang; Qi Chen; Feng Gao; Zhi-Guo Zhang; Yongfang Li. “Directed assembly of cathode interlayers enables efficient binary organic solar cells.” *Nature Energy*, published 20 October 2026. Original paper: [https://doi.org/10.1038/s41560-026-02148-w](https://doi.org/10.1038/s41560-026-02148-w?ref=research-pop.com) --- ## Research POP Notes This article reflects the independent interpretation of the Research POP team and does not represent the views of the authors, their institutions or the journal. If you identify any inaccuracies or have concerns regarding the content, figures or attribution, please contact us at [team.researchpop@gmail.com](mailto:team.researchpop@gmail.com). We will review the matter promptly and make corrections or remove the relevant material where appropriate.