Sputtered Zn(O,S)/In2O3:H window layers for enhanced blue response of chalcopyrite solar cells

A combination of undoped ZnO and ZnO:Al is the most commonly used window layer stack for chalcopyrite solar cells. The high carrier density and thickness required to achieve a sufficiently low sheet resistance lead to optical absorption and cause losses in photocurrent, in particular in monolithically interconnected modules. Additionally, the band gap of the CdS buffer layer and of un-doped ZnO limit the blue response. These losses could be avoided by using a transparent conductive oxide with high carrier mobility and wider band gap in combination with a buffer layer which also has a wide band gap. We propose a stack of Zn(O,S) and In2O3:H and report on our first results concerning its implementation. This stack is Cd-free, highly transparent over a wide range, and can be deposited completely by sputtering which is an industrially proven dry process. (© 2015 WILEY-VCH Verlag GmbH &Co. KGaA, Weinheim)