Effects of RbF postdeposition treatment and heat-light soaking on the metastable acceptor activation of CuInSe₂ thin film photovoltaic devices

Granular particles formed on a CuInSe₂ (CIS) thin film surface with alkali-halide RbF post-deposition treatment (RbF-PDT) are found to concentrate preferably on other than smooth (112)-planes present on the CIS film surface. As a consequence, a large number of distinctive pores are selectively formed at relatively rough facets. Although the open circuit voltage and fill factor values of CIS solar cells improve with either RbF-PDT or heat-light soaking (HLS) treatment, the effects of these treatments are distinguishable. The ratio of carrier recombination rates at the interface (Rⁱ) to that in the bulk (R^b), namely, Rⁱ/R^b, decreases with RbF-PDT. HLS treatment performed on RbF-PDT CIS devices leads to a further decrease in the value of Rⁱ/R^b, whereas the value of Rⁱ/R^b of CIS devices fabricated without RbF-PDT increases with HLS treatment. Ternary CIS solar cells grown with RbF-PDT and HLS treatment reproducibly demonstrate enhanced photovoltaic efficiencies.