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Suppressed recombination loss in organic photovoltaics adopting a planar–mixed heterojunction architecture

Abstract

At present, high-performance organic photovoltaics mostly adopt a bulk-heterojunction architecture, in which exciton dissociation is facilitated by charge-transfer states formed at numerous donor–acceptor (D-A) heterojunctions. However, the spin character of charge-transfer states originated from recombination of photocarriers allows relaxation to the lowest-energy triplet exciton (T1) at these heterojunctions, causing photocurrent loss. Here we find that this loss pathway can be alleviated in sequentially processed planar–mixed heterojunction (PMHJ) devices, employing donor and acceptor with intrinsically weaker exciton binding strengths. The reduced D-A intermixing in PMHJ alleviates non-geminate recombination at D-A contacts, limiting the chance of relaxation, thus suppressing T1 formation without sacrificing exciton dissociation efficiency. This resulted in devices with high power conversion efficiencies of >19%. We elucidate the working mechanisms for PMHJs and discuss the implications for material design, device engineering and photophysics, thus providing a comprehensive grounding for future organic photovoltaics to reach their full promise.

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Fig. 1: The Jablonski diagram and the active materials used for OPV fabrication.
Fig. 2: Photovoltaic cells characterizations.
Fig. 3: TA results and MD-simulated DSE dimers of neat materials.
Fig. 4: TA results of different blends.

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Data availability

The authors declare all data supporting the findings of this study are available within the manuscript and the Supplementary Information. The .cif files corresponding to single-crystal structures reported in this work are available from Cambridge Crystallographic Data Centre (T9TBO-F: 2081901; T9SBN-F: 2084244 and 2081902). The source data of Supplementary Table 2 and Supplementary Fig. 6c,d are provided as Supplementary Data 1 and 2.

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Acknowledgements

The work has been supported by the sponsorship of the Lee Shau-Kee Chair Professor (Materials Science; A.K.-Y.J.); the City University of Hong Kong under the APRC Grant 9380086 (A.K.-Y.J.); the Innovation and Technology Commission of Hong Kong under the TCFS Grant GHP/018/20SZ (A.K.-Y.J.) and MRP Grant MRP/040/21X (A.K.-Y.J.); the Environment and Ecology Bureau of Hong Kong under the Green Tech Fund 202020164 (A.K.-Y.J.); the US Office of Naval Research under the grant numbers N00014-20-1-2191 (A.K.-Y.J.), N000141712204 (Z.P. and H.A.) and N000142012155 (Z.P. and H.A.); the Research Grants Council of Hong Kong under General Research Fund 11307621 (A.K.-Y.J.) and 11316422 (A.K.-Y.J.), the Collaborative Research Fund C6023-19GF (A.K.-Y.J.) and the Hong Kong Postdoctoral Fellowship Scheme (F.R.L.); the Guangdong Major Project of Basic and Applied Basic Research under the grant number 2019B030302007 (A.K.-Y.J.); the Guangdong-Hong Kong-Macao Joint Laboratory of Optoelectronic and Magnetic Functional Materials under the grant number 2019B121205002 (A.K.-Y.J.); the National Key R&D Program of China under the grant numbers 2017YFA0303703 (C. Zhang), and 2018YFA0209100 (C. Zhang); the Fundamental Research Funds for the Central Universities under the grant number 0204-14380177 (C. Zhang); the National Natural Science Foundation of China under the grant numbers 22225305 (C. Zhang), 21922302 (C. Zhang), 21873047 (C. Zhang), 52002393 (J.Z.) and 51873160 (C. Zhong). The authors also gratefully acknowledge H. Zhang and Z. Cai from the Hong Kong Baptist University for the experimental assistances on MALDI-ToF measurements, and S. B. Jo from the Sungkyunkwan University for his help on analysing TA data.

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Authors

Contributions

K.J., F.R.L., J.Z., C. Zhang and A.K.-Y.J. conceived the project. K.J., F.R.L. and J.Z. designed the experiments. K.J. fabricated and characterized the cells. F.R.L. and F.Q. synthesized the materials and grew the single crystals. J.Z., Q.L., M.X. and C. Zhang conducted TA experiments and corresponding analysis. C. Zhong conducted the MD, density functional theory and Marcus rate calculations. W.K. solved the single-crystal structures. S.H.J. and F.R.L. analysed the molecular interactions in single crystals. Z.P. and H.A. carried out the GIWAXS and RSoXS experiments and corresponding analysis. J.Z., J.Y. and F.G. carried out the photovoltage loss measurements and corresponding analysis. X.D. provided help on optical measurements. H.H. carried out the ToF-SIMS measurement. D.S. carried out the UPS measurement. F.R.L., K.J., J.Z., C. Zhang and A.K.-Y.J. wrote the manuscript with input from all authors. A.K.-Y.J. and C. Zhang supervised the study.

Corresponding authors

Correspondence to Francis R. Lin, Chunfeng Zhang or Alex K.-Y. Jen.

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Supplementary Information

Supplementary Figs 1–107, Tables 1–19, Notes I–VI and Scheme 1.

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Supplementary Data 1

PV parameters behind the statistics of Supplementary Table 2.

Supplementary Data 2

PV parameters behind the statistics of Supplementary Figures 6c,d.

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Jiang, K., Zhang, J., Zhong, C. et al. Suppressed recombination loss in organic photovoltaics adopting a planar–mixed heterojunction architecture. Nat Energy 7, 1076–1086 (2022). https://doi.org/10.1038/s41560-022-01138-y

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