Low-temperature water-processed NiO hole transport layers for high-efficiency CH3NH3PbI3 perovskite solar cells

Solution-processed NiO film is widely applied as the hole transport layer (HTL) of metal halide perovskite solar cells (PSCs). In general, a process temperature over 300 degrees C is necessary to improve the nucleation and crystallization of NiO grains. This temperature is higher than the glass transition temperature of most low-cost flexible substrates. In this paper, NiO nanoparticle water solution was prepared to spin-coat NiO films at a treatment temperature of 100 degrees C. The solar cell with the invert planar structure of ITO/NiO/CH3NH3PbI3/ZnO/Ag presented a power conversion efficiency of 11.24 %, which is comparable with that of similar CH3NH3PbI3 solar cells with the NiO HTLs prepared at the high temperature. The water-processed NiO HTL greatly decreases the process temperature and simplifies the preparation process of PSCs, showing promising applications in low-cost flexible PSCs.