Cesium Doped NiO x as an Efficient Hole Extraction Layer for Inverted Planar Perovskite Solar Cells

Abstract Organic–inorganic hybrid perovskite solar cells have resulted in tremendous interest in developing next generation photovoltaics due to high record efficiency exceeding 22%. For inverted structure perovskite solar cells, the hole extraction layers play a significant role in achieving efficient and stable perovskite solar cell by modifying charge extraction, interfacial recombination losses, and band alignment. Here, cesium doped NiO x is selected as a hole extraction layer to study the impact of Cs dopant on the optoelectronic properties of NiO x and the photovoltaic performance. Cs doped NiO x films are prepared by a simple solution‐based method. Both doped and undoped NiO x films are smooth and highly transparent, while the Cs doped NiO x exhibits better electron conductivity and higher work function. Therefore, Cs doping results in a significant improvement in the performance of NiO x ‐based inverted planar perovskite solar cells. The best efficiency of Cs doped NiO x devices is 19.35%, and those devices show high stability as well. The improved efficiency in devices with Cs:NiO x is attributed to a significant improvement in the hole extraction and better band alignment compared to undoped NiO x . This work reveals that Cs doped NiO x is very promising hole extraction material for high and stable inverted perovskite solar cells.