Texture-etched ZnO as a versatile base for optical back reflectors with well-designed surface morphologies for application in thin film solar cells

ZnO layers with a wide range of surface morphologies were studied for applications in thin film silicon solar cells. The texture of ZnO layers, achieved by chemical etching, was measured by atomic force microscopy (AFM) and statistically analyzed in terms of the roughness, the crater depth, the crater diameter, and the crater opening angle. We present a method to independently tune the lateral and vertical dimensions of the etched crater structures by combined variations of ZnO layer thickness and etching time. The optical scattering properties of the textured ZnO layers are investigated. The effects of these morphologies on the performance of the solar cells, prepared in both pin and nip configurations are analyzed. For the latter cell type the roughness is introduced at the back side, thus the cell does not sense ZnO absorption and conductivity of the different morphologies. The link between the morphology, the optical properties of ZnO layers, and the solar cell performance is discussed.