Face-centered cubic p-type NiO films room-temperature prepared via direct-current reactive magnetron sputtering-Influence of sputtering power on microstructure, optical and electrical behaviors

High-quality p-type NiO films are crucial for NiO-based heterojunction solar cells. Herein, a series of face-centered cubic, p-type NiO films was prepared at room temperature through DC reactive magnetron sputtering. The increased sputtering power (SP) improves the film crystallization. The film's lattice strain is increased and a microstress transition from compressive to tensile stress occurs with increased SP. The film's lattice strain reduces the LO and 2LO phonon frequency. The blueshifted optical absorption edge with increased SP is caused by the improved film crystallization. The film's free hole concentration is slightly increased and subsequently reduced with increased SP. The former is mainly due to the increased number of the nickel vacancies, whereas the latter to the improved film crystallization that reduces the content of the nickel vacancies and interstitial oxygen. The hole mobility is strongly affected by the scatterings by the crystal lattice and point defects.