Cesium- and Chlorine-Doped MAPbI3 Perovskites under Open-Air Conditions for Efficient and Stable Photovoltaic Devices

Nowadays, methylamine lead iodine (MAPbI3) perovskite materials with excellent photoelectric properties have been widely concerned. However, the poor material stability and the undesired film quality of MAPbI3 perovskites in air ambient seriously hamper their further development. Hence, we fabricated a series of Cs+ or Cl--doped CsxMA1-xPbI3 and MAPbI3-yCly films by one-step solution deposition method under open-air conditions to improve the thermal stability and crystallinity of MAPbI3 films, and systematically investigated the influence of doping ions. Results indicate that a small amount of Cs+ can improve the thermal stability of the MAPbI3 film and the power conversion efficiency (PCE) of the PSCs. However, excessive Cs⁺ doping may induce phase segregation, leading to the formation of δ-phase CsPbI3 and consequently deteriorating the performance of PSCs. Meanwhile，minor Cl⁻ incorporation markedly enlarges grain size in MAPbI3 films. After optimizing the doping contents of Cs+ and Cl-, we obtained the best Cs0.1MA0.9PbI3 and MAPbI2.5Cl0.05 PSCs, showing a maximum PCE of 19.61% and 19.56%, respectively. Subsequently, we further improve the performance of MAPbI3 films by co-doping with optimal concentrations of Cs⁺ and Cl⁻. Results indicate that, compared with MAPbI3-based devices, the Cs0.1MA0.9PbI2.95Cl0.05-based devices exhibit a longer carrier lifetime and a lower defect density. Consequently, the best-performance Cs0.1MA0.9PbI2.95Cl0.05 PSCs attain a remarkable PCE of 20.10% and a Voc of 1.14 V in air, surpassing the PCE of devices with either Cs⁺ or Cl⁻ incorporation alone. Moreover, the thermal stability of the Cs0.1MA0.9PbI2.95Cl0.05-based devices was also significantly improved compared to that of MAPbI3. Furthermore, by optimizing the thickness and sputtering process of the IZO transparent electrode, we successfully fabricated semi-transparent perovskite solar cells (ST-PSCs) with a PCE of 17.73%.