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Elucidating the photodegradation pathways of polymer donors for organic solar cells with seven months of outdoor operational stability

Nature Photonics volume 19, pages 415–425 (2025)Cite this article

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Abstract

The operating lifetime under real-world climates is a critical metric to evaluate the commercial potential of any photovoltaic technology. Organic solar cells (OSCs) have experienced rapid breakthroughs in performance over the past decade owing to advances in device and materials engineering, including interfaces, electron acceptors, and donors. However, the intrinsic photodegradation of polymer donors remains poorly understood, and a path to stable OSCs is yet to be demonstrated under outdoor testing conditions. Herein we elucidate the side-chain-induced degradation mechanism in polymer donors and present an outdoor stability database covering 15 representative non-fullerene-based OSCs, supported by in-lab photostability and thermostability analysis. By understanding the performance losses induced by several photoactive layers and interfaces, we demonstrate that encapsulated non-fullerene-based OSCs can retain 91% of the initial efficiency after seven months of operation under hot and sunny Saudi Arabian climates. These findings reveal encouraging prospects of non-fullerene-based OSCs for outdoor applications.

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Fig. 1: Photodegradation and device mechanisms of OSCs.
Fig. 2: Photochemical degradation of polymer donors.
Fig. 3: Tracking morphological changes of donor:Y6-based blends at nanometre scale.
Fig. 4: Generality of side-chain-induced photodegradation in the studied polymer donors.
Fig. 5: Outdoor stability of the OSC devices.
Fig. 6: Seven-month outdoor stability of the cells from September 2022 to April 2023.

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Data availability

We declare that the data supporting the findings of this study are available within this paper and its Supplementary Information. Alternative formats for raw data files may be requested from the corresponding author on reasonable request. The raw data for the NMR spectra (Extended Data Fig. 3) and the outdoor stability database (Extended Data Fig. 8) are available in the data files provided with this paper. Source Data are provided with this paper.

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Acknowledgements

This publication is based on work supported by the King Abdullah University of Science and Technology (KAUST) Office of Sponsored Research (OSR) under award no. CCF-3079. J.H. expresses gratitude to the Alexander von Humboldt Foundation and the support during his stay in T. B. Marder’s group at Julius-Maximilians-Universität Würzburg. H.X. would like to extend thanks to A. V. Marsh and M. Heeney for providing the training and technical support related to the GPC instrumentation. We would like to thank the KAUST weather team for providing access to weather station data. We acknowledge the use of the KAUST Solar Center and the support from its staff.

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Author notes

  1. These authors contributed equally: Han Xu, Jianhua Han.

Authors and Affiliations

  1. Material Science and Engineering Program (MSE), Physical Sciences and Engineering Division (PSE), King Abdullah University of Science and Technology (KAUST), Thuwal, Kingdom of Saudi Arabia

    Han Xu, Jianhua Han, Maxime Babics, Luis Huerta Hernandez, Diego Rosas Villalva, Jules Bertrandie, Yongcao Zhang, Ye Liu, Hu Chen, Joel Troughton, Frédéric Laquai, Stefaan De Wolf & Derya Baran

  2. Institut für Anorganische Chemie and Institute for Sustainable Chemistry and Catalysis with Boron (ICB), Julius-Maximilians-Universität Würzburg, Am Hubland, Würzburg, Germany

    Jianhua Han

  3. POLYMAT, University of the Basque Country UPV/EHU, San Sebastian, Spain

    Matteo Sanviti & Jaime Martin

  4. Universidade da Coruña, Campus Industrial de Ferrol, CITENI, Esteiro, Ferrol, Spain

    Matteo Sanviti & Jaime Martin

  5. School of Physical Sciences, Great Bay University, Dongguan, China

    Hu Chen

  6. Imaging and Characterization Core Lab, King Abdullah University of Science and Technology (KAUST), Thuwal, Saudi Arabia

    Lingyun Zhao

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  1. Han Xu
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Contributions

D.B. conceived the idea and directed the project. H.X. and J.H. designed the experiments, fabricated the solar cells and conducted the DFT calculations. M.B. and S.D.W. conducted the encapsulation of outdoor solar cells and outdoor stability measurements (Fig. 5d). L.H.H., J.B. and J.T. built the outdoor set-up and conducted outdoor stability measurements for PM6, D18 and PCE10-based devices (Fig. 5a). H.C. and H.X. performed the GPC measurements. Y.L., D.R.V. and H.X. conducted the Raman spectra measurements. D.R.V. conducted the GIWAXS and GISAXS measurements. M.S. and J.M. performed the GISAXS fitting analysis. L.Z. conducted the HR-TEM measurements. Y.Z. performed the AFM measurements and assisted in the fabrication of OFETs. F.L., S.D.W. and D.B. supervised the project and contributed to the manuscript. The manuscript was written by H.X. and J.H. and edited by all of the co-authors.

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Correspondence to Derya Baran.

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Extended data

Extended Data Fig. 1 Investigation of the contribution of BHJ layers and interfaces to the photodegradation of PM6:Y6-based devices.

(a) Scheme of the device fabrication and photo-aging conditions (plasma lamp with a spectrum close to AM1.5 G, N2 atmosphere) for understanding the role of interface stability. (b) J-V curves of the fresh and 200-hour aged-PM6:Y6-based devices. (c) TPC lifetime and (d) fitted n values (VOC versus Plight) for the fresh and 200-hour aged-PM6:Y6-based devices. (e) PV parameters for the fresh and 200-hour aged devices. Herein, both half-cell aged-PM6:Y6- and PCE10:Y6-based devices were examined to demonstrate further the role of BHJ and interface stability. It is also noteworthy, as reported in the literature57, that photochemical degradation of polymer donors could also be a source that induces chemical changes at interfaces between BHJ and transport layers, contributing to device degradation. The error bars represent the s.d. of independent measurements: n = 8 for PM6:Y6 and n = 6 for PCE10:Y6. Initial PCEs for the fresh-PM6:Y6-based devices: 14.9(14.8 ± 0.1)% and the fresh PCE10:Y6-based devices: 8.9(8.7 ± 0.2)%. The increased TPC lifetimes, decreased PCEs, changes in the fitted n values (VOC versus Plight)40, and VOC changes between aged-PEDOT:PSS:BHJ-based devices and aged full-cells demonstrate that the PCE losses come from both the degradation of the BHJ layer and interface. The detailed PV parameters are provided in Supplementary Table 3.

Extended Data Fig. 2 Investigation of the contribution of polymer donor PM6 and acceptor Y6 to the photodegradation of PM6:Y6 devices.

(a) Scheme of the fabrication of aged-PM6:fresh-Y6 and fresh-PM6:aged-Y6 devices (with fresh interlayers). Photo-aging condition: plasma lamp with a spectrum close to AM1.5 G, N2 atmosphere. (b) J-V curves of the aged-PM6:fresh-Y6 and fresh-PM6:aged-Y6 devices. Photovoltaic parameters are summarized in Supplementary Table 3. (c–e) The exciton dissociation and charge collection efficiency, TPC and TPV lifetime, α and n values for the 200-hour aged devices. We also subjected PCE10 to 200-hour photo-aging and subsequently fabricated the devices using fresh-Y6 and fresh interlayers, and Supplementary Fig. 12c shows that the devices based on aged-PCE10:fresh-Y6 still demonstrate stable PCEs compared to the fresh devices. To further elucidate the photodegradation effects of PM6 and Y6, we extended the photo-aging process from 200 hours to 500 hours. Notably, after 500 hours of extended aging, insoluble by-products formed when dissolving PM6 in CHCl3 during device fabrication, accompanied by an increase in solution viscosity. Although mixing aged-PM6 with fresh-Y6 is different from the one with in-situ photodegradation in the blends (due to the formation of insoluble photodegraded products and the remixing process of PM6:Y6), herein, we can observe the existence of photodegradation of PM6, which agrees with the reported work46,47.

Extended Data Fig. 3 NMR spectra of the fresh, 500-hour aged, and 1000-hour aged polymer thin films.

a, NMR spectra from the fresh and aged PM6 films. b, NMR spectra from the fresh and aged D18 films. c, NMR spectra from the fresh and aged PCE10 films. The NMR spectra of polymer donors were recorded in CDCl3 with a concentration of 1 mg/mL (Supplementary Figs. 52–60). In addition to the proven side-chain-induced degradation for classic polymer donors in the literature21,26,27,28,29,31, the appearance of new peaks at ~1.21 and ~1.18 ppm in Extended Data Fig. 3 for all three aged polymer donors also offers chemical evidence for the side-chain-induced photodegradation pathway. It is worth mentioning that insoluble solids were formed in CDCl3 solution for the aged D18 sample. These results agree with the NMR spectra in the literature and the side-chain degradation for dioxythiophene-based conjugated polymers reported by Reynolds et al.26. Source data for all the NMR spectra are provided with this paper.

Source data

Extended Data Fig. 4 Raman spectra and GPC curves of the polymer donors.

(a) Raman spectra and (b) GPC curves of the polymer thin films before and after photo-aging. Discussion on Raman and GPC changes arising from side-chain cross-linking, see Supplementary Note 4. The simulated Raman spectra of polymer donors and their degradation modes are presented in Supplementary Figs. 17–29. The Raman spectra for 500-hour aged polymer films are presented in Supplementary Fig. 35. The LBO values and chemical structures of the model polymers for DFT calculations are presented in Supplementary Figs. 33. PCE10 with BDT-TT linkage is more photostable than PTQ10 in the absence of O2, see discussion in Supplementary Fig. 39.

Extended Data Fig. 5 Optimization of interfaces for outdoor stability measurements.

(a) Thermal stability of PM6:Y6 blends with the PDINO and PNDIT-F3N interfaces. The error bars represent the s.d. of independent measurements. Initial PCEs: PDINO-based devices (65 °C): 14.3(14.1 ± 0.1)%, n = 6. Stability data for PDINO-based devices (RT, storage stability) and PNDIT-F3N-based devices (65 °C) is extracted from Supplementary Fig. 32 and Fig. 5b. (b) Photostability of PM6:Y6, D18:Y6, and PCE10:Y6 blends with the PNDIT-F3N interface. Initial PCEs: 15.0%, 15.1%, 9.3%; (c) PCEs, (d) TPC lifetimes, and (e) fitted n values (VOC versus Plight) for the PM6:Y6-based devices with different photo-aging conditions. Error bars in Extended Data Fig. 5c represent the s.d. of the mean, with the centres indicating the mean values. Data are presented as mean values +/− s.d., with the maximum values shown in parentheses. Initial PCEs for the PNDIT-F3N-based devices: 15.9(15.4 ± 0.3)%, n = 8; Full-cell stability data in Extended Data Fig. 5c is extracted from Fig. 1c (PDINO-based devices) and Extended Data Fig. 5b (PNDIT-F3N-based devices). TPC lifetimes and n values (VOC versus Plight) for PDINO-based devices are extracted from Extended Data Fig. 1. Herein, PDINO is more photostable than PNDIT-F3N, fitting for investigating the BHJ photostability in devices. PNDIT-F3N is thermally stable and can suppressed the thermal diffusion effect within/across the interlayers under heat stress, fitting for the outdoor stability testing58. The results also show that the PCE losses come from both the BHJ layer and interface degradation.

Extended Data Fig. 6 Irradiance and temperature effect on outdoor performance of the PM6-, D18-, and PCE10-based devices.

a, Temperature-dependent J-V curves of PM6:Y6. b, Temperature-dependent J-V curves of D18:Y6. c, Temperature-dependent J-V curves of PCE10:Y6. d, Efficiency evolutions of the devices on 16th September 2022 at different irradiance. e, Efficiency evolutions of the devices on 16th September 2022 at different time. Due to the spectra difference (AM 1.5 G and solar irradiance at KAUST) and temperature effect59, the calculated PCEs from outdoor data (PCE*) are different from the PCEs under standard AM 1.5 G condition measured in-lab (details in Supplementary Fig. 49 and Table 8). In this study, we calculated PCEs based on the highest power output values during PM 12:00-12:30.

Extended Data Fig. 7 Photo-, thermal, and outdoor stability of the PM6:PCE13:PY-IT-based ternary devices.

(a) PCE13 with fragile S-containing side-chains (LBO values in Supplementary Fig. 50). (b) Photostability of the PM6:PCE13:PY-IT-based ternary devices. Initial PCEs for the devices: PM6:PY-IT (15.4%); PCE13:PY-IT (11.3%); PM6:PCE13:PY-IT (0.95:0.05:1, 15.9%); PM6:PCE13:PY-IT (0.9:0.1:1, 15.7%). The photostability test was conducted under open-circuit conditions at 27 °C, using AM 1.5 G 100 mW cm−2 illumination in an N2 atmosphere. Notably, different from the direct energetic trap states caused by the tiny oxidized fullerenes in blends24, the introduction of small amount of guest polymer donor with unstable side-chains had a negligible impact on the photo- and outdoor stability of ternary OSCs. When transitioning to the comparable binary systems, it becomes evident that PM6-based devices is more photostable than the PCE13-based devices. (c) Thermal stability of the PM6:PCE13:PY-IT-based ternary devices. Initial photovoltaic parameters are listed in Supplementary Table 9. The error bars represent the s.d. of independent measurements (n = 6), and the centres represent the average values. (d) outdoor stability of the PM6:PCE13:PY-IT-based ternary devices. Initial PCEs for the encapsulated devices: PM6:PY-IT (15.1/14.4/15.0%); PCE13:PY-IT (7.7/7.6/7.4%); PM6: PCE13:PY-IT (0.95:0.05:1, 12.8/13.7/13.5%); PM6:PCE13:PY-IT (0.9:0.1:1, 13.4/14.2/14.0%).

Extended Data Fig. 8 Summary of the outdoor stability testing located in the KAUST testing site, Saudi Arabia.

Poutput is the power output of the devices under outdoor conditions. The highest Poutput during the first and last day were utilized to compare the outdoor stability, and the devices in the same group were aged under identical real-world climates. The whiskers represent the maximum and minimum values, and the box edges indicate the 75th and 25th percentiles. The center lines in the box-plot chart indicate the mean values. In group 2, the first 4-week outdoor stability database for PM6:N3, PM6:BTP-BO-4Cl, and PM6:BTP-eC9 blends, and the first 60-day outdoor stability database for PM6:Y12, PM6:Y6, and PM6:Y7 blends are available from the previous work11. All the outdoor stability database is available in the source data files provided with this paper.

Source data

Supplementary information

Source data

Source Data Extended Data Fig. 3

Unprocessed NMR Source Data.

Source Data Extended Data Fig. 8

Raw data for the outdoor stability database.

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Xu, H., Han, J., Babics, M. et al. Elucidating the photodegradation pathways of polymer donors for organic solar cells with seven months of outdoor operational stability. Nat. Photon. 19, 415–425 (2025). https://doi.org/10.1038/s41566-025-01644-x

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