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Emissive and charge-generating donor–acceptor interfaces for organic optoelectronics with low voltage losses

Abstract

Intermolecular charge-transfer states at the interface between electron donating (D) and accepting (A) materials are crucial for the operation of organic solar cells but can also be exploited for organic light-emitting diodes1,2. Non-radiative charge-transfer state decay is dominant in state-of-the-art D–A-based organic solar cells and is responsible for large voltage losses and relatively low power-conversion efficiencies as well as electroluminescence external quantum yields in the 0.01–0.0001% range3,4. In contrast, the electroluminescence external quantum yield reaches up to 16% in D–A-based organic light-emitting diodes5,6,7. Here, we show that proper control of charge-transfer state properties allows simultaneous occurrence of a high photovoltaic and emission quantum yield within a single, visible-light-emitting D–A system. This leads to ultralow-emission turn-on voltages as well as significantly reduced voltage losses upon solar illumination. These results unify the description of the electro-optical properties of charge-transfer states in organic optoelectronic devices and foster the use of organic D–A blends in energy conversion applications involving visible and ultraviolet photons8,9,10,11.

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Fig. 1: Studied material systems, reciprocity relation between CT absorption and emission, and current–voltage characteristics.
Fig. 2: Temperature-dependent Voc and the EL measurements.
Fig. 3: Open-circuit voltage and non-radiative voltage losses as a function of ECT.

Data availability

The data that support the plots within this paper and other findings of this study are available from the corresponding authors upon reasonable request.

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Acknowledgements

This work was supported by the German Federal Ministry for Education and Research (BMBF) through the InnoProfile project ‘Organische p–i–n Bauelemente 2.2’ (03IPT602X) and by the German Research Foundation (DFG) project Photogen (VA 1035/5-1). X.J. and Y.L. acknowledge support from the China Scholarship Council (nos. 201706140127 and 201506920047, respectively). The authors also acknowledge the DFG for supporting K.T. (project 382633022 ‘RECOLPER’), F.P., S.Ro. and D.N. (SFB 951 ‘HIOS’) and A.F. (RE 3198/6-1 ‘EFOD’).

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S.U., J.B., X.J., D.S. and K.V. designed the experiments, prepared photovoltaic devices and optimized their processing parameters for photovoltaic performance. S.U., X.J., Y.L. and J.W. performed temperature-dependent characterization of the devices. J.B. and X.J. measured the sensitive EQEPV spectra. K.T., V.C.N., F.P. and S.Ro. measured the EQEEL and corresponding electroluminescence spectra. D.N., A.F., S.Re. and K.V. supervised sub-tasks (OPV and OLED design, investigation and data interpretation) within the project and participated in discussions of the findings. K.V. supervised the overall project. All authors contributed to the data analysis and writing of the manuscript.

Corresponding authors

Correspondence to Sascha Ullbrich or Johannes Benduhn or Koen Vandewal.

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Supplementary Tables 1–5, Supplementary Figures 1–8, Supplementary References 1–35

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Ullbrich, S., Benduhn, J., Jia, X. et al. Emissive and charge-generating donor–acceptor interfaces for organic optoelectronics with low voltage losses. Nat. Mater. 18, 459–464 (2019). https://doi.org/10.1038/s41563-019-0324-5

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