High‐Purity Inorganic Perovskite Films for Solar Cells with 9.72 % Efficiency.

Abstract: All‐inorganic perovskite solar cells with high efficiency and improved stability are promising for commercialization. A multistep solution‐processing method was developed to fabricate high‐purity inorganic CsPbBr3 perovskite films for use in efficient solar cells. By tuning the number of deposition cycles (<italic>n</italic>) of a CsBr solution, the phase conversion from CsPb2Br5 (<italic>n</italic> ≤3), to CsPbBr3 (<italic>n=</italic>4), and Cs4PbBr6 (<italic>n</italic>≥5) was optimized to achieve vertical‐ and monolayer‐aligned grains. Upon interfacial modification with graphene quantum dots, the all‐inorganic perovskite solar cell (without a hole‐transporting layer) achieved a power conversion efficiency (PCE) as high as 9.72 % under standard solar illumination conditions. Under challenging conditions, such as 90 % relative humidity (RH) at 25 °C or 80 °C at zero humidity, the optimized device retained 87 % PCE over 130 days or 95 % over 40 days, compared to the initial efficiency. [ABSTRACT FROM AUTHOR]