Novel etch process to tune crater size on magnetron sputtered ZnO:Al

Abstract

Magnetron sputtered aluminum-doped zinc oxide (ZnO:Al) is used as a window layer in silicon-based thin-film solar cells due to its high transparency, high conductivity, and ability to provide effective light trapping after etching in a dilute HCl solution. A challenge with this method is the strong influence of sputtering conditions on the density and shape of the ZnO:Al etch features. Here we present a novel chemical etch process based on HF that enables the modification of surface features through the etch process itself, thus allowing the separate optimization of ZnO:Al deposition and texturization. The different etch characteristics of HCl and HF are studied on single crystal ZnO. Using the different etch characteristics of HF we effectively texturize polycrystalline ZnO:Al films which previously exhibited only poor light trapping in silicon thin-film solar cells. The light trapping improvement is seen by an 18% increase in short circuit current density when used in microcrystalline silicon solar cells. Additionally, using mixtures of HCl and HF we are able to tune the feature size and shape on a given ZnO:Al sample. Scanning electron microscope images of high-rate deposited ZnO:Al etched in HCl and HF. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.