Zinc as a New Dopant for NiO_x-Based Planar Perovskite Solar Cells with Stable Efficiency near 20%

Organic–inorganic lead halide perovskite solar cells are potential alternatives to commercial silicon solar cells because of their attractive photon conversion efficiency and general material costs, except for the widely adopted organic hole-transporting polymers, which are currently expensive and have low conductivity. Inorganic hole-transporting layers (HTLs) have recently garnered attention due to their excellent stability and relatively effective cost. Nickel oxide (NiOx) is a typical p-type oxide semiconductor with a deep valence band (VB) and is expected to be used as HTL. Unfortunately, the charge extraction efficiency has been hindered by its poor conductivity, resulting in lower efficiency when compared with organic HTL-based devices. Here, we report a new solution-processed doping strategy for NiOx with zinc dopant to improve its conductivity for perovskite solar cells. The NiOx:Zn HTL showed high transparency and significantly enhanced electrical conductivity in comparison with the pristine NiOx. Our best NiOx:Zn-based P-i-N planar device showed an efficiency of 19.6% with negligible hysteresis, which is comparable with the reported planar solar cell with an organic HTL. Moreover, the NiOx:Zn-based perovskite device displayed distinguished stability in ambient conditions. This paper demonstrated important progress toward high-efficiency planar perovskite devices with low-cost inorganic HTLs.