Enhancing Efficiency of Inverted Perovskite Solar Cells by Sputtered Nickel Oxide Hole-Transport Layers

Perovskite solar cells (PSCs) are now approaching their theoretical limits and the optimization of the auxiliary layers is crucial for fully exploiting the potential of perovskite materials. In this study, NiO_x as a hole-transport layer (HTL) for inverted p–i–n PSCs is focused on. Sputtered NiO_x is an attractive p-type HTL owing to its facile processing, wide energy bandgap that prevents electron transfer, high transparency, stability, and effective hole extraction. Despite substantial research on sputtered NiO_x, the relationship between the carrier concentration and work function is still unclear. In this study, the use of sputtered NiO_x as a widely compatible HTL and the effect of its thickness on PSC device performance are investigated. Inverted PSCs with the optimal 10 nm thick NiO_x achieve a remarkable power conversion efficiency of 20.54%, which is the highest reported to date for sputtered NiO_x-based PSCs. Furthermore, PSCs with various NiO_x thicknesses demonstrate similar performances, demonstrating the excellent versatility of NiO_x for use with different perovskite absorbers. The devices exhibit excellent thermal and photostability, retaining 97% of their initial power conversion efficiency at 65 °C and 1 sun illumination for 350 h. Sputtered NiO_x HTLs have great potential for use with diverse perovskite compositions and PSC structures.