Abstract
A nickel oxide (NiO (x) ) hole transport layer was made from nickel oxide powder by a simple process and non-stabilizer or chelating agent. We used ethanol as the main solvent and less than 2% nitric acid as the co-solvent. The formation reaction mechanism of the NiO (x) thin film was also studied. Perovskite solar cells (PSCs) with an optimum thickness of 70 nm exhibited a power conversion efficiency as high as 12.99%, which is superior to those of PSCs with their counterparts. The moisture stability of NiO (x)-based devices (non-encapsulated) remained above 70% of their initial output after 700 h storage at ambient conditions.