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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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 126.96.36.199 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.
The authors declare no competing interests.
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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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