Influence of the Ga Content on the Optical and Electrical Properties of CuIn $_{{\bm 1}\hbox{--}{\bm x}}$Ga $_{\bm x}$Se$_{\bm 2}$ Thin-Film Solar Cells

Thin-film solar cells that are based on Cu(In,Ga)Se
₂
(CIGS) absorbers with Ga/(Ga+In)-ratios from 0 to 1 are fabricated, and their optical and electrical properties are investigated by macroscopic (current density-voltage, external quantum efficiency) and microscopic (Kelvin probe force microscopy on untreated cross sections of solar cells) measurements. Combining all results, the diffusion voltages of individual solar cells are deduced and compared with the directly measured open-circuit voltages. An increasing splitoff between the diffusion voltage and the open-circuit voltage is observed for Ga addition, which indicates a higher recombination rate of photogenerated charge carriers in solar cells with higher Ga content.