CuInSe2 absorber layer grown under copper excess with a copper poor surface formed by a KF post deposition treatment

Abstract

The post deposition treatment (PDT) of chalcopyrite absorber layers with heavy alkalis leads to an increase in power conversion efficiencies in CI(G)S solar cells. Here, we present an in-situ treatment with etching step on CuInSe 2 absorber layers grown under copper excess, which improves the open circuit voltage (Voc), the fill factor (FF) and power conversion efficiency. Low temperature photoluminescence measurements show that besides the stoichiometric absorber a second copper deficient phase is present near the surface after the PDT. Calibrated photoluminescence measurements reveal that there is an improvement in quasi Fermi level splitting after treatment contributing to the improved Voc.