CuIn1-xGaxSe2 thin film solar cells by two-selenizations process using Se vapor

A novel process consisting of two-selenizations of magnetron sputtered metallic precursors using Se vapor and a method for Ga incorporation using a single Cu-Ga(22 at.%) alloy target without deleterious indium-gallium interaction have been developed for preparation of well-adherent, large, compact, well faceted-polyhedral-grain CuIn1-xGaxSe2 thin films having optimum composition of Cu:In:Ga:Se in atomic percent of 24.25:22.21:4.40:49.14. Higher indium proportion in the first precursor resulted in elimination of pits in the CuIn1-xGaxSe2 films, which made them more suitable for preparation of solar cells with thin CdS heterojunction partner layers. Optimized selenization parameters with the maximum temperature of 550-560°C and a Se vapor incidence rate of 50-75 angstrom s-1 resulted in improved morphology and enhanced gallium content of completed CuIn1-xGaxSe2 thin films. The best solar cell had an open-circuit voltage Voc of 451.8 mV, a short-circuit current density Jsc of 34.5 mA, a fill factor of 57.87%, a total-area efficiency of 9.02%, and a fairly constant spectral response over the entire spectral range.