Bandgap tuning of a CsPbBr3 perovskite with synergistically improved quality via Sn2+ doping for high-performance carbon-based inorganic perovskite solar cells

Abstract

Narrowing the bandgap and promoting the quality of inorganic perovskites are the key points to improve the performance of inorganic perovskite solar cells. Herein, we incorporate Sn²⁺ into an inorganic CsPbBr₃ perovskite to simultaneously tune the bandgap and improve the quality of the perovskite film. The density functional theory calculations demonstrate that the incorporation of Sn²⁺ leads to an obvious shift of the conduction band minimum of the CsPbBr₃ perovskite towards the lower energy region. Therefore, the bandgap of CsPb_1−xSn_xBr₃ perovskites is gradually reduced with the increase of the Sn²⁺ content. Additionally, when Pb²⁺ is substituted with an appropriate amount of Sn²⁺, the doped perovskite films display largely promoted quality compared to the undoped one. These advantages lead to the suppression of charge recombination and the enhancement of light harvesting in the as-fabricated perovskite solar cells (PSCs). Consequently, the CsPb_0.95Sn_0.05Br₃-based PSC with a structure of FTO/TiO₂ layer/perovskite/carbon delivers a greatly promoted power conversion efficiency of 8.04% compared with the efficiency of 5.93% for the controlled device. Moreover, the CsPb_0.95Sn_0.05Br₃ PSC without any encapsulation preserves over 91% of its initial efficiency after 720 h of storage in ambient air, suggesting an excellent stability.