Solar Cells Based on Cu(In, Ga)Se2 Thin-Film Layers

Abstract

This paper presents the results of experimental studies of spectral, dark current–voltage and light load characteristics of the selenide–copper–gallium–indium (Cu(In, Ga)Se2) solar cell. Тhe main fundamental parameters of the photoactive semiconductor layer Cu(In, Ga)Se2, such as the band gap, the resistivity of the layer, the equilibrium majority–carrier concentration, the lifetime and the product μnτn of nonequilibrium minority carriers from the spectral, photoelectric and dark current–voltage characteristics are determined. Based on an analysis of the light-load current–voltage characteristics at various solar radiation powers (50–1000 W/m2), the main parameters of the p–n junction were determined, as well as the nonideality factor and the magnitude of the reverse diode saturation current; a photogeneration mechanism was established in the studied solar radiation range, which had the character of a diffusion mechanism, where carrier recombination in the photoactive layer did not have a significant effect. We found that in conditions of real solar lighting (Рrad = 50–1000 W/m2), the output parameters of the solar cell – short-circuit current, open circuit voltage, the maximum output power increases with Рrad. The fill factor (FF) of the light-current–voltage characteristics has a maximum at Рrad ≈ 200 W/m2, and an efficiency has a maximum value at Рrad ≈ 600 W/m2. The observed dependences of FF and efficiency are explained by the dependence of the series (Rser) and shunt (Rsh) resistance of a solar cell on Prad. To maintain the efficiency of a solar cell based on thin-film layers Cu(In, Ga)Se2, equally high in conditions of increased radiation, as well as in conditions of low solar radiation, it is necessary that Rser decreases and Rsh does not change with Prad.