Adjusting the Introduction of Cations for Highly Efficient and Stable Perovskite Solar Cells Based on (FAPbI₃)_0.9(FAPbBr₃)_0.1

Although the power conversion efficiency (PCE) of perovskite solar cells (PSCs) has increased to 22.7 %, the instability when exposed to moisture and heat has hindered their further practical development. In this study, to gain highly efficient and stable perovskite components, methylammonium (MA), Cs, and Rb cations are introduced into a (FAPbI₃)_0.9(FAPbBr₃)_0.1 (FA=formamidine) film, which is rarely used because of its poor photovoltaic performance. The effects of different contents of MA, Cs, or Rb cations on the performance of (FAPbI₃)_0.9(FAPbBr₃)_0.1 films and devices are systematically studied. The results show that the devices with Cs cations exhibit markedly improved photovoltaic performance and stability, attributed to the clearly enhanced quality of films and their intrinsic stability. The (FAPbI₃)_0.9(FAPbBr₃)_0.1 devices with 10 % Cs show a PCE as high as 19.94 %. More importantly, the unsealed devices retain about 80 % and 90 % of the initial PCE at 85 °C after 260 h and under 45±5 % relative humidity (RH) after 1440 h, respectively, which are better than that with 15 % MA and 5 % Rb under the same conditions. This indicates that a highly efficient and stable perovskite component has been achieved, and PSCs based on this component are expected to promote their further development.