High-performance transparent ultraviolet photodetector based on thermally reduced graphene oxide and ZnO thin films

A transparent planar electrode from thermally reduced graphene oxide (TRGO) incorporated with a photoconductive thin film of zinc oxide (ZnO) was successfully employed in a visible-blind ultraviolet (UV) photodetector. The TRGO layer was obtained from thermal reduction of drop-cast GO layer at the temperature of 400 °C after which the electrical resistance of layer decreased four orders of magnitude to ~100 Ω. Then a pure and uniform ZnO thin film with the thickness of ~80 nm was sputtered on the TRGO layer. High UV absorption and visible transparency with the average transmittance of 92% in the range of 400–800 nm (T400−800) were obtained for the ZnO thin film. Moreover, the TRGO layer was highly capable in collecting photogenerated electrons from ZnO thin film and efficient transport of charge carriers to the contact electrodes. The ZnO/TRGO device showed an ideal Ohmic behavior and high visible-light transparency with T400−800 = 80%. Furthermore, the results of current–time measurements with cyclic exposure of the device to UV light indicated stable ON/OFF switching states and highly repeatable photoresponse.