Synergistic Effect of Codoped Nickel Oxide Hole–Transporting Layers for Highly Efficient Inverted Perovskite Solar Cells

Abstract

Inverted perovskite solar cells (PSCs), which feature an attractive structure for diverse applications such as tandem SCs or flexible devices, continue to be rapidly developed. Among various hole‐transporting layer (HTL) materials, nickel oxide (NiO x ) is widely used as a stable and superior HTL even though it exhibits poor conductivity. Although various methods have been proposed to overcome the low conductivity of NiO x films, codoping methods have not been extensively studied and remain poorly understood. Herein, Li:Cu:NiO x is systematically investigated to explore the synergistic effect of codoping in various NiO x HTLs and PSCs. The optical, chemical, and morphological properties of the films are characterized and the dependence of these properties on the codoping ratio are investigated. A gradual improvement of the electrical properties and a tunable Fermi energy level resulting from the Li:Cu codopants is subsequently demonstrated. Furthermore, the structure of the perovskite films on HTLs and the synergistic effect on the preferred crystal growth behavior are elucidated. An inverted PSC with high efficiency was attained as a result of the enhanced electrical properties of the NiO x HTLs and the high quality of the perovskite film, which were attributed to the synergistic effect of the Li:Cu codoping method.