Effect of bath temperature on the efficiency and properties of Cu2O/ZnS/ZnO heterojunctions thin film prepared by electrodeposition and chemical bath deposition methods

A novel p-n type Cu2O/ZnS/ZnO heterojunction thin film was successfully fabricated by a combination of electrodeposition and chemical bath deposition techniques. The effect of bath temperature (T = 75, 80, 85, 90 degrees C) on the growth of ZnS layers was investigated. The influence of ZnS buffer layers on the properties and efficiency of the prepared heterojunction thin films were examined using XRD, FE-SEM, AFM, EDS, UV-Vis, and electrochemical measurements. The analysis of prepared films revealed that the Cu2O/ZnS/ZnO heterojunction exhibits a unique combination of hexagonal structure of ZnO and the cubic structure of Cu2O. It was found that all the heterojunction films exhibit the growth of composed pyramids and corner grains with a homogenous distribution. The optical band-gap of the deposited ZnS buffer layers decreased from 3.46 eV to 3.35 eV with an increase of bath temperature from 75 degrees C to 90 degrees C. Moreover, the obtained results revealed that the thicknesses and the surface roughness of ZnS buffer layers increased when bath temperature increased. Mott-Schottky results of the heterojunctions indicate a p-type semiconductor behavior for the Cu2O, while it was observed an n-type semiconductor behavior for the ZnO and ZnS layers. As a result, the photocurrent response of Cu2O/ZnO heterojunctions with ZnS layer insertion was enhanced from 0.175 to 0.730 mA, which can be attributed to the reduced electron transfer resistance, enlarged photo-generated (e-/h(+)) carrier separation efficiency, and enhanced light absorption due to the presence of ZnS buffer layers. These results highlight the advantages of the bath temperature on the deposition of ZnS for photoelectrochemical and solar cells applications