Solution-processed 100 nm size Ag and Au nanoparticles (NPs) were included in p-n diodes based on ZnO:Ga (GZO)/p-Si heterojunction. The NPs were deposited using spin-coating process on GZO layer. The inclusion of these particles led to improved optical absorption and consequently increased the performance of the devices in terms of photoelectric properties. Generally, higher performance was demonstrated by the Ag NPs-coated device. The devices were highly sensitive to UV illumination. Photoresponsivity (PR) of 0.73 A W-1 at-3 V was exhibited by the Ag NPs-coated device against 0.60 and 0.54 A W-1 for the Au NPs-coated and without NPs (bare) devices, respectively. The devices also demonstrated a photovoltaic (PV) behaviour under AM1.5 illumination. Compared to the bare device, significant improvement of 167.3% in the short circuit current (I-sc) and 83.1% in the PV conversion efficiency were obtained with the Ag NPs-coated device.