Influence of Se beam pressure on deep-level defects in Cu(In,Ga)Se_2 thin films studied by photocapacitance and time-resolved photoluminescence measurements

Abstract

The properties of deep-level defects in Cu(In,Ga)Se2 thin films grown under different Se beam pressure were investigated by photocapacitance (PC) and time-resolved photoluminescence (TRPL) measurements. A generally known deep-level defect located at around 0.8 eV above the valence band was identified for all samples by transient photocapacitance measurement, the position of which was unvaried with the Se beam pressure. The defect concentration and the capture cross section of the minority carrier were obtained from the steady-state photocapacitance and TRPL measurements, which were evaluated to be on the order of 1013 cm−3 and 10−14 cm2, respectively, in the Se beam pressure range from 1.3×10−3 to 4.4×10−3 Pa. The relatively higher defect concentration and larger minority carrier capture cross section were considered as possible causes of the degradation of the conversion efficiency of CIGS solar cells grown under low Se beam pressure.