Surface modification of CsPbI2Br perovskite film with an organic ammonium salt for efficient photovoltaics

To date, the best efficiency of organic-inorganic hybrid perovskite solar cells (PSCs) has reached 25.7%, but the volatile nature of organic compounds at high temperature results in their poor thermal stability. All-inorganic perovskites such as CsPbI2Br, possess excellent thermal stability, but the power conversion efficiency (PCE) of CsPbI2Br PSCs still lag far behind their organic-inorganic perovskite counterparts. To enhance the PCE of CsPbI2Br PSCs, an organic ammonium salt, namely benzylamine hydroiodide (BZAI) has been adopted to modify the surface of CsPbI2Br films. The BZA+ can interact with Iˉ and Brˉ on the surface of CsPbI2Br film to passivate perovskite surface defects. In addition, the BZAI interfacial layer can finely adjust the energy levels of CsPbI2Br perovskite to match with the hole transporting layer (HTL), and thus reduce the charge recombination at the perovskite/HTL interface. Finally, the PCE of the devices is notably increased from 12.87% to 15.08% after introducing the BZAI interfacial layer, and the device stability in nitrogen environment is also improved.