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Design rules for minimizing voltage losses in high-efficiency organic solar cells

Abstract

The open-circuit voltage of organic solar cells is usually lower than the values achieved in inorganic or perovskite photovoltaic devices with comparable bandgaps. Energy losses during charge separation at the donor–acceptor interface and non-radiative recombination are among the main causes of such voltage losses. Here we combine spectroscopic and quantum-chemistry approaches to identify key rules for minimizing voltage losses: (1) a low energy offset between donor and acceptor molecular states and (2) high photoluminescence yield of the low-gap material in the blend. Following these rules, we present a range of existing and new donor–acceptor systems that combine efficient photocurrent generation with electroluminescence yield up to 0.03%, leading to non-radiative voltage losses as small as 0.21 V. This study provides a rationale to explain and further improve the performance of recently demonstrated high-open-circuit-voltage organic solar cells.

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Fig. 1: Low-energy offset material systems and their photovoltaic performance.
Fig. 2: Spectroscopic studies on devices and solid films.
Fig. 3: Transient absorption characterization of the most efficient OSC systems under study.
Fig. 4: Description of relevant electronic states and (non)radiative transitions.

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Acknowledgements

The authors thank J. Durrant, J.-S. Kim, M. Pshenichnikov and D. Paraschuk for useful discussions. The research was supported by the Swedish Energy Agency Energimyndigheten (grant no. 2016-010174), the Swedish Research Council VR (grant nos 621-2013-5561, 2016-06146, and 2017-00744), the Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linköping University (faculty grant no. SFO-Mat-LiU #2009-00971), the National Natural Science Foundation of China (grants nos 91633301, 51673201 and 21325419), the Chinese Academy of Sciences (grant no. XDB12030200), the China Scholarship Council (CSC) (no. 201306730002) and the Department of the Navy, Office of Naval Research, under the MURI ‘Center for Advanced Organic Photovoltaics’ (awards nos N00014-14-1-0580 and N00014-16-1-2520). F.G. is a Wallenberg Academy Fellow and O.I. is a Wallenberg Scholar. A.A.B. is a Royal Society University Research Fellow. This project has also received funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (grant agreement nos 639750 and 717026). W.T. acknowledges an Ambizione fellowship from the Swiss National Science Foundation.

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The authors declare no competing interests.

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Contributions

F.G. conceived and directed the project. D.Q. fabricated the solar cell devices, performed the FTPS, steady-state photoluminescence, electroluminescence and EQEEL experiments. Z.Z. carried out the DFT calculations. X.L. performed the PLQE measurements. S.C. and G.P. carried out the transient photoluminescence measurements. H.F.Y., J.L., S.S.C. and S.L. synthesized the materials. T.R.H. and A.A.B. carried out the transient absorption measurements. T.R.H., J.Z. and A.A.B. analysed the time-resolved data. B.G. and Y.J. fabricated the solar cell devices. L.O. performed the cyclic voltammetry measurements. D.Q. was supervised by F.G. and F.Z. J.B. and V.C. supervised the DFT calculations. J.H. and H.Y. supervised the materials synthesis and device fabrication. I.B. and W.C. supervised the transient photoluminescence measurements. W.T., O.I. and F.Z. participated in data interpretation. D.Q., W.T., T.R.H., V.C., A.A.B. and F.G. wrote the manuscript. All authors discussed the results and commented on the final manuscript.

Corresponding authors

Correspondence to Veaceslav Coropceanu or Artem A. Bakulin or Feng Gao.

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Supplementary Figures 1–18, Supplementary Tables 1–10, Supplementary References 1–8

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Qian, D., Zheng, Z., Yao, H. et al. Design rules for minimizing voltage losses in high-efficiency organic solar cells. Nature Mater 17, 703–709 (2018). https://doi.org/10.1038/s41563-018-0128-z

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