Effect of first-stage temperature on Cu(In,Ga)Se2 solar cells using the evaporation of binary selenide compounds

Cu(In,Ga)Se2 films were prepared by a three-stage process using the evaporation of In2Se3, Ga2Se3, Cu2Se, and Se. In the first stage, the (In,Ga)2Se3 layer was deposited at the substrate temperatures of 150°C and 325°C by the evaporation of In2Se3, Ga2Se3, and Se. The CIGS film had small grains with a bi-layer morphology at 150°C, while the film had large grains without the bi-layer morphology at 325°C. As the first-stage temperature increased, the CdS/Cu(In,Ga)Se2 solar efficiency was improved from 9.3% to 11.7% for 0.21 cm2 active area. The efficiency improvement was attributed to the reduction of the recombination at the CdS/Cu(In,Ga)Se2 interface and recombination within Cu(In,Ga)Se2 film bulk due to the increase of Cu(In,Ga)Se2 grain size. These findings were supported by the increased hole density, reduced reverse saturation current, and enhanced spectral response with increasing the first-stage temperature.