An optically transparent p-n heterojunction device consisting of p-NiO and n-ZnO thin films was fabricated by r.f. sputtering method. The structural and optical properties of the p-NiO/n-ZnO heterojunction were characterized by X-ray diffraction (XRD). UV-visible spectroscopy, Hall effect measurement, and J-V photocurrent measurements. The XRD shows that ZnO films are highly crystalline in nature with preferred orientation along the (0 0 0 2) direction. The p-NiO/n-ZnO heterojunction device has an average transmittance of over 80% in the visible region. The current-voltage curve of the heterojunction demonstrates obvious rectifying diode behavior in a dark environment. The lowest leakage current is 6.64 x 10(-8) A/cm(2) for the p-NiO/n-ZnO heterojunction device. (C) 2011 Elsevier Ltd. All rights reserved.