The effect of temperature on resistive ZnO layers and the performance of thin film CdTe solar cells

The use of a highly resistive transparent (HRT) layer has been shown to increase the efficiency of thin film CdTe heterostructure solar cells incorporating a thin CdS layer. In this study ZnO HRT layers were deposited at different substrate temperatures on soda lime glass and on fluorine-doped tin oxide-coated glass to enable structural, optical and electrical characterization. The performance of equivalent films was tested within CdS/CdTe solar cells. The ZnO thickness was limited to 150 nm, whilst the substrate temperature was varied from 20 degrees C to 400 degrees C during deposition. X-ray diffraction patterns and transmission electron microscopy of the cross-sectional microstructure of completed devices showed that the growth of the ZnO is improved when the films are deposited at higher temperatures. Film resistivity was lowest at 100 degrees C and highest at 400 degrees C, ranging from 10(-2) Omega.cm to 033 Omega.cm. The high temperature deposited ZnO exhibits improved micro-structural growth and an improvement in device efficiency. (C) 2016 The Authors. Published by Elsevier B.V.