Optoelectronic Modulation of Undoped NiO_x Films for Inverted Perovskite Solar Cells via Intrinsic Defect Regulation

Ni vacancy (VNi) as an intrinsic defect plays an important role in the optical and electronic properties of NiOx films for inverted planar perovskite solar cell (PSC) applications. This work presents a facile method to fabricate highly dense and continuous NiOx films with excellent optical transmittance and electronic conductivity by pulsed laser deposition. By simply adjusting the preparation parameters, including oxygen partial pressure, postannealing temperature, and duration time, the well-regulated VNi defects contribute to the modified conductivity and optical transmittance of the NiOx films. The conductivity and optical transmittance of NiOx films are all dramatically enhanced with the increasing oxygen partial pressure. Specifically, the valence band level of NiOx is adjusted by the VNi defect densities to better match or align with that of the perovskite layer for faster hole extraction with lower energy losses. Density functional theory calculation displays that the Fermi energy level is shifted to a lower energy level due to the enhanced hole carrier concentration generated from the increased VNi. Benefiting from the excellent optical transmittance, electronic conductivity, and well-matched energy alignment, the inverted PSC with NiOx hole transport layer (HTL) exhibits the highest power conversion efficiency of 16.85% with high open-circuit voltage (1.14 V), short-circuit current density (20.49 mA/cm2), fill factor (0.72), and negligible current–voltage hysteresis effect. This work reveals that modulating the intrinsic defects of NiOx HTLs is an efficient way to achieve high performance of NiOx-based inverted PSCs.