Environmental stability of highly conductive nominally undoped ZnO layers

Highly conductive nominally undoped ZnO (b-ZnO) films represent an attractive alternative for ZnO:Al windows employed in thin film solar cells. In order to assess their suitability for the PV industry, we examine here their stability in various environments. We show that the b-ZnO films can exhibit comparable stability to ZnO:Al films in both ambient and heated air. However, b-ZnO films degrade faster in accelerated open damp heat (DH) conditions, which can be related to their columnar microstructure. Finally, a b-ZnO multilayer coating with an improved environmental stability is presented.