Photovoltaic activity of ZnO nanorods arrays co-sensitized by CdS and CuInS₂ quantum dots

One-dimensional ZnO nanorods arrays were self-assembly grown on a ZnO thin film, and then CdS quantum dots were deposited on the ZnO nanorods arrays by a successive ionic layer adsorption and reaction process. Scanning electron microscopy and transmission electron microscopy results indicate that the CdS quantum dots can be uniformly deposited on the ZnO nanorods arrays and the thickness of the CdS shell can be controlled through varying the number of the adsorption and reaction cycle. For a typical sample prepared by the adsorption and reaction cycles of 10 times, the thickness of the CdS is about 4.0 nm. Monodispersed CuInS₂ quantum dots with a size of 3.5 nm were synthesized by a solvothermal route and then deposited on the ZnO nanorods arrays coated with the CdS quantum dots by using an electrophoretic deposition technique. Optical and electrical properties indicate that the as-fabricated ZnO/CdS/CuInS₂ heterojunction structure not only exhibits a high absorption of the incident light in visible region but also can reduce a leakage current as compared to the ZnO/CdS heterojunction structure. Electrical impedance spectroscopy is used to analyze the electrochemical reaction of the interfaces.