Formation of CdS Thin Film on Different Substrates Using Electrochemical Atomic Layer Deposition (E-ALD)

Abstract

With solar energy being a promising alternative to fossil fuels, the need for high quality and high efficiency photovoltaic (PV) materials is obvious. As a major component in thin film solar cells, CdS thin film can be combined with absorber layers such as CdTe or CIGS (Cu, In, Ga, Se) to form p-n junction for light energy conversion.1 Electrochemical deposition is a low cost and controllable method for the fabrication of CdS thin films. Electrochemical atomic layer deposition (E-ALD) is the electrochemical form of atomic layer deposition that utilizes surface limited reaction to deposit one or less than one layer of element each time.2-3 High quality thin films can be using E-ALD but may take a relatively long time. Thus E-ALD is particularly suitable for making CdS films where a thickness as low as 50 nm is sufficient for the heterojunction formation.4 CdS thin films on Au have been made using E-ALD, and the film thickness increases linearly with increasing cycle number. The resulting CdS thin film is a single crystal with cubic <111> structure. SEM images show a conformal coating of CdS on Au substrate with a grain size of around 70 nm. The same method is applied to form CdS thin film on Ag and Ag nanorods for enhanced photoelectrochemical response. Preliminary study of CdS deposition on indium-tin-oxide (ITO) has been conducted by reducing the oxide substrate to a minimum amount of metallic surface to increase the nucleation sites for film growth.