This work investigates the impact of annealing on the performance of p-CuO/n-Si heterojunction, where the CuO nano-powder is synthesized by using CBD technique and subsequently used to grow CuO thin films by employing vapour-liquid-solid method. Investigations are performed in terms of film morphology, crystallite structure and photovoltaic performances. The photovoltaic parameters including open circuit photo-generated voltage, short-circuit current density and energy conversion efficiency are estimated by measuring the current-voltage characteristics of p-CuO/n-Si diodes under illumination. The power conversion efficiencies are obtained to be 0.26% and 6.13% for the as-deposited and annealed films respectively, for a power input of 0.037 mW/cm2.