Vanadium oxide (V2O5-x) thin films with a thickness of about 4 nm were prepared by atomic layer deposition (ALD) to be used as a hole-transporting layer in an amorphous silicon solar cell. The ALD growth characteristics (growth rate, crystallinity, and surface morphology) of the V2O5-x films were investigated while exposed to different pulse times of ozone (O-3), which was used as an oxidant. The effect of the different ozone pulse times, used in the V2O5 layer, on the device performance was also investigated. At the ozone pulse time of 1 s, the maximum value of power conversion efficiency (PCE), i.e., 5.35%, was achieved, whereas at the ozone pulse time of 5 s, the PCE was 4.18%. Ultraviolet photoelectron spectroscopy (UPS) and X-ray photoelectron spectroscopy (XPS) analyses confirmed that increasing the proportion of crystalline phase in the V2O4 films with lower work function of V2O5 resulted in decreased open-circuit voltage and conversion efficiency as the ozone pulse time increased. (C) 2015 Elsevier B.V. All rights reserved.