Combustion Processed Nickel Oxide and Zinc Doped Nickel Oxide Thin Films as a Hole Transport Layer for Perovskite Solar Cells

Combustion processed nickel oxide (NiOx) thin film is considered as an alternative to the sol-gel processed hole transport layer for perovskite solar cells (PSCs). In this paper, NiOx thin film was prepared by the solution–combustion process at 250 °C, a temperature lower than the actual reaction temperature. Furthermore, the properties of the NiOx hole transport layer (HTL) in PSCs were enhanced by the incorporation of zinc (Zn) in NiOx thin films. X-ray diffraction and X-ray photoelectron spectroscopy results revealed that the formation of NiOx was achieved at lower annealing temperature, which confirms the process of the combustion reaction. The electrical conductivity was greatly improved with Zn doping into the NiOx crystal lattice. Better photoluminescence (PL) quenching, and low PL lifetime decay were responsible for better charge separation in 5% Zn doped NiOx, which results in improved device performance of PSCs. The maximum power conversion efficiency of inverted PSCs made with pristine NiOx and 5% Zn-NiOx as the HTL was 13.62% and 14.87%, respectively. Both the devices exhibited better stability than the PEDOT:PSS (control) device in an ambient condition.