Investigation of the properties of deep-level defect in Cu(In,Ga)Se2 thin films by steady-state photocapacitance and time-resolved photoluminescence measurements

Abstract

The quantitative characterization of the deep-level defect located at around 0.8 eV above the valence band in Cu(In1−x,Gax)Se2 (CIGS) thin films was performed by steady-state photocapacitance (SSPC) and time-resolved photoluminescence (TRPL) measurements. The defect concentration, photoionization cross section and electron capture cross section were evaluated to be on the order of 1013–1014 cm−3, 10−17–10−16 cm2, and 10−14 cm2, respectively, in the Ga content x range from 0.30 to 0.80; the first two values increased with increasing Ga content while the last one remained almost constant. By comparing the obtained values with the actual device performance, the cause of the degradation of the conversion efficiency of CIGS solar cells with higher Ga content was discussed in relation to the 0.8 eV defect.