Direct-current-sputtered nickel oxide (NiO) films with improved p-type conduction characteristic: impact of substrate temperature on structure, optical and electrical properties

Abstract Nickel oxide (NiO) films are direct current sputtered at different substrate temperatures (T sub ) using high sputtering power density and sputtering pressure. The improvement in crystallization of the films with T sub results in the decrease of concentration of the coexisting Ni vacancies and interstitial O atoms, thereby increasing the hole mobility and resistivity. All the films have an approximate near-violet absorption edge of ca. 3.6 eV. The only difference is the rate of increase of transmittance that is attributed to the tail states produced by the tensile stress. The polycrystalline NiO film with 200 °C T sub can be used as the hole-transporting layer material of inverse-architecture perovskite solar cells due to the maximum free hole concentration, minimum resistivity and intermediate hole mobility.