Inorganic ammonium salt doping in nickel oxide for highly efficient planar perovskite solar cells

Abstract Inverted perovskite solar cells (PSCs) have stood out in recent years for their great potential in offering low‐temperature compatibility, long‐term stability and tandem cell suitability. However, challenges persist, particularly concerning the use of nickel oxide nanoparticles (NiO x NPs) as the hole transport material, where issues such as low conductivity, impurity‐induced aggregation and interface redox reactions significantly hinder device performance. In response, this study presents a novel synthesis method for NiO x NPs, leveraging the introduction of ammonium salt dopants (NH 4 Cl and NH 4 SCN), and the solar cell utilizing the doped NiO x substrate exhibits much enhanced device performance. Furthermore, doped solar cells reach 23.27% power conversion efficiency (PCE) when a self‐assembled monolayer (SAM) is further employed. This study provides critical insights into the synthesis and growth pathways of NiO x NPs, propelling the development of efficient hole transport materials for high‐performance PSCs.