Electroreflectance of CuInS2 thin film solar cells and dependence on process parameters

The electroreflectance (ER) of CuInS2 thin film solar cells prepared by seq uential processing is investigated as a function of the process parameters Cu/In ratio and sulfurization temperature in order to get a better understa nding of the growth mechanisms. A detailed interpretation of the ER spectra is presented. The disappearance of the ER signal under indium-rich conditi ons is explained by a superficial CuIn5S8 secondary phase. An additional st ructure in ER spectra below the band gap energy is attributed to electroabs orption and is explained by the transition between copper vacancies and sul fur vacancies in CuInS2 as identified by photoluminescence. The strong depe ndence of this electroabsorption structure on the process parameters and th e occurrence of the superficial CuIn5S8 secondary phase is explained by pha se transitions in the equilibrium phase diagrams of the metal sulfides form ed during sulfurization. (C) 2001 American Institute of Physics.