On the role of non‐doped ZnO in CIGSe solar cells

Abstract

ABSTRACTWe investigate the role of the non‐doped i‐ZnO layer in thin‐film Cu(In,Ga)Se2 solar cells. A large number of laboratory scale module cells with different non‐doped ZnO thicknesses are inspected by JV analysis, lock‐in thermography and optical spectroscopy. We find that the role of the i‐ZnO layer in our samples is to reduce the impact of randomly occurring electrical shunt paths in the devices. Accordingly, the i‐ZnO layer leads to a somewhat smaller spread of device parameters. In the case of absent shunt paths, the device parameters of cells and modules without i‐ZnO are similar to those with a thin i‐ZnO layer. An effect of i‐ZnO on the Voc is not systematically observed. However, for larger i‐ZnO thickness, Jsc is systematically reduced, which is identified as due to optical absorption in the i‐ZnO layer. We further find by high‐resolution lock‐in thermography that the junction homogeneity is not affected by the i‐ZnO layer. Only the non‐linear reverse bias current reduces with increasing i‐ZnO thickness—an effect that appears to be independent from the saturation current density. Copyright © 2011 John Wiley & Sons, Ltd.