CsPbBrI2 perovskites with low energy loss for high-performance indoor and outdoor photovoltaics

Over the years, the efficiency of inorganic perovskite solar cells (PSCs) has increased at an unprecedented pace. However, energy loss in the device has limited a further increase in efficiency and commercialization. In this work, we used (NH4)2C2O4·H2O to treat CsPbBrI2 perovskite film during spin-coating. The CsPbBrI2 underwent secondary crystallization to form high quality films with micrometer-scale and low trap density. (NH4)2C2O4·H2O treatment promoted charge transfer capacity and reduced the ideal factor. It also dropped the energy loss from 0.80 to 0.64 eV. The resulting device delivered a power conversion efficiency (PCE) of 16.55% with an open-circuit voltage (Voc) of 1.24 V, which are largely improved compared with the reference device which exhibited a PCE of 13.27% and a Voc of 1.10 V. In addition, the optimized treated device presented a record indoor PCE of 28.48% under a fluorescent lamp of 1000 lux, better than that of the reference device (19.05%).