Cu-rich CuInSe₂solar cells with a Cu-poor surface

Abstract

We present the effects of an In-Se surface treatment of Cu-rich ([Cu]/[In] > 1) CuInSe2 absorbers in order to utilize the superior transport properties of Cu-rich absorbers for high-efficiency solar cells. A Cu-poor surface was successfully formed on a Cu-rich absorber by co-evaporation of indium and selenium under appropriate conditions. The aim is to suppress the interface recombination, which is generally observed at the interface between CdS and Cu-rich CuInSe2. A surface-treated device achieved an efficiency of 13.1%, improved from 9.5% obtained with an untreated Cu-rich device. The open-circuit voltage of In–Se treated devices reach the same level as devices made from Cu-poor absorbers grown by a three-stage process. By comparing the results of the experiments and simulations, it is shown that the role of the Cu-poor surface on Cu-rich absorbers is to prevent interface recombination, mainly due to a lower doping level of the Cu-poor surface layer than in the Cu-rich CuInSe2. Thus, it becomes possible to uncouple the interface from the bulk properties in Cu-rich solar cells. Copyright © 2014 John Wiley & Sons, Ltd.