Influence of post-deposition selenium supply on Cu(In,Ga)Se2-based solar cell properties

Cu(In,Ga)Se2 (CIGSe) layers have been deposited by the 3-stage process and once the growth was completed, the structures have been kept at high temperature for 50 min with or without Se supply. Both the resulting CIGSe layer and related device properties are compared with those obtained when the substrate is cooled down right after the deposition. Moreover, such experiments have been performed with and without alkali availability. The results show that keeping the absorber at high temperature differently impacts [Ga] / ([In + Ga]) atomic ratio distribution and crystalline preferential orientation depending on whether Se is supplied. Moreover, this work shows that chalcogen supply can be detrimental for cell performance when the CIGSe contains alkali and in contrast be beneficial when the CIGSe is free of alkali. These observations suggest an intimate relationship between alkali and Se.