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

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 (n) of a CsBr solution, the phase conversion from CsPb2Br5 (n 3), to CsPbBr3 (n=4), and Cs4PbBr6 (n5) 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 degrees C or 80 degrees C at zero humidity, the optimized device retained 87% PCE over 130days or 95% over 40days, compared to the initial efficiency.