Development of high-efficiency CuInxGa1-xSe 2 thin-film solar cells by selenization with elemental Se vapor in vacuum

On the basis of the establishment of the two-stage method developed in this study which is directly linked to the control of the Se beam-flux intensity during the precursor preparation stage, achievements in the development of CIGS thin-film absorbers are reported with remarkably high efficiency of 14.9% in the band gap of about 1.3 eV. Furthermore, it is demonstrated for the first time, that the two-stage method developed in this study is applicable to the formation of a graded band-gap structure by adjusting the Se beam-flux intensity during the precursor preparation stage to over 1.5×10^-5 Torr, which leads to rather high efficiency of 10.1%. These results demonstrate (1) a significantly high capability of the two-stage method developed in this study to prepare device-quality CIGS thin-film absorbers and (2) the control of Se is the most important factor to fabricate a sufficiently high-quality CIGS thin-film absorber in this method