Fine-tuning of the chemical structure of photoactive materials for highly efficient organic photovoltaics

Abstract

The performance of organic photovoltaics is largely dependent on the balance of short-circuit current density (JSC) and open-circuit voltage (VOC). For instance, the reduction of the active materials’ optical bandgap, which increases the JSC, would inevitably lead to a concomitant reduction in VOC. Here, we demonstrate that careful tuning of the chemical structure of photoactive materials can enhance both JSC and VOC simultaneously. Non-fullerene organic photovoltaics based on a well-matched materials combination exhibit a certified high power conversion efficiency of 12.25% on a device area of 1 cm2. By combining Fourier-transform photocurrent spectroscopy and electroluminescence, we show the existence of a low but non-negligible charge transfer state as the possible origin of VOC loss. This study highlights that the reduction of the bandgap to improve the efficiency requires a careful materials design to minimize non-radiative VOC losses.

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Fig. 1: Chemical structures, and optical and electrochemical properties of the photoactive materials.
Fig. 2: Photovoltaic performance of devices based on different material combinations.
Fig. 3: Morphology of neat and blend films.
Fig. 4: Energy loss analysis.

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 financially supported by the Ministry of Science and Technology (no. 2014CB643501) and the National Natural Science Foundation of China (nos 91633301, 51521002, 51673069, 21520102006 and 21822505). N.L. gratefully acknowledges financial support from the DFG research grant BR 4031/13-1, the ETI funding at FAU Erlangen-Nürnberg, and the Bavarian Ministry of Economic Affairs and Media, Energy and Technology by funding the HI-ERN (IEK11) of FZ Jülich. C.J.B. gratefully acknowledges financial support through the ‘Aufbruch Bayern’ initiative of the state of Bavaria (EnCN and ‘Solar Factory of the Future’), the Bavarian Initiative ‘Solar Technologies go Hybrid’ (SolTech), the SFB 953 (DFG) and the Cluster of Excellence ‘Engineering of Advanced Materials’ (EAM) at FAU Erlangen-Nürnberg. RSoXS was performed at beamline 11.0.1.2 and GIWAXS was performed at beamline 7.3.3 at the Advanced Light Source of Lawrence Berkeley National Laboratory (LBNL), which was supported by the DOE, Office of Science and Office of Basic Energy Sciences. We acknowledge the support for film sample preparation at the Molecular Foundry, LBNL. Work at the Molecular Foundry was supported by the Office of Science, Office of Basic Energy Sciences, of the US Department of Energy under contract no. DE-AC02-05CH11231.

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B.F., L.Y., N.L. and F.H. conceived the ideas and coordinated the work. B.F. and L.Y. designed the donor polymers. B.F. synthesized the polymers, conducted the ultraviolet–visible and cyclic voltammetric measurements, performed the device fabrication and characterization, and analysed the data. X.D. and X.T. conducted the FTPS and EL measurements. X.D. analysed the FTPS and EL data. X.T. performed the temperature-dependent J–V characterization. R.X. synthesized the acceptor molecules. F.L., W.Z., J.X. and W.M. conducted the GIWAXS measurements and analysed the data. F.L. and W.Z. performed the RSoXS measurements and analysed the data. K.A. performed the light-intensity-dependent J–V characterization. N.L. assisted with the large-area device fabrication and evaluation. B.F., L.Y., N.L., C.J.B., F.H. and Y.C. contributed to manuscript preparation. All authors commented on the manuscript.

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Correspondence to Lei Ying or Ning Li or Fei Huang.

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Fan, B., Du, X., Liu, F. et al. Fine-tuning of the chemical structure of photoactive materials for highly efficient organic photovoltaics. Nat Energy 3, 1051–1058 (2018). https://doi.org/10.1038/s41560-018-0263-4

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