Microstructured ZnO coatings combined with antireflective layers for light management in photovoltaic devices

We describe microstructured ZnO coatings that improve photovoltaic (PV) device performance through their antireflective properties and their tendency to scatter incoming light at large angles. In many PV devices, reflection from the transparent conductive top contact significantly degrades performance. Traditional quarter-wave antireflective (AR) coatings reduce surface reflection but perform optimally for only a narrow spectral range and incident illumination angle. Furthermore, in some types of devices, absorption far from the junction increases the rate of recombination, and light management strategies are required to remedy this. The randomly patterned, microstructured ZnO coatings described in this paper, formed via a simple wet etch process, serve as both an AR layer with superior performance to that of a thin film AR coating alone as well as a large angle forward scatterer. We model formation of the coatings and evaluate their AR properties. When combined with a traditional quarter-wave MgF2 coating, these microstructured ZnO coatings increase short circuit currents of example Cu(In,Ga)Se-2 (CIGS) devices by over 20% in comparison to those of uncoated devices at normal incidence. A similar improvement is observed for illumination angles of up to 60 degrees. While demonstrated here for CIGS, these structures may prove useful for other PV technologies as well. Published 2016. This article is a U.S. Government work and is in the public domain in the USA. Progress in Photovoltaics: Research and Applications Published by John Wiley & Sons Ltd.