Photoluminescence characterization of surface degradation mechanism in Cu(In,Ga)Se2 thin films grown on Mo/soda lime glass substrate

Abstract

Intensity and decay time of a near-band-edge photoluminescence (PL) of a Cu(In,Ga)Se2 (CIGS) thin film grown on a Mo/soda lime glass (SLG) substrate decreased with air exposure time, showing the degradation of the CIGS film surface. The dependence of Mo sputtering conditions on intensity and decay time of PL was studied in CIGS films deposited on Mo/SLG substrates. The Mo/SiO2 (20 nm)/SLG substrate was used to control Na diffusion during CIGS deposition. Intensity and decay time of PL with time in air changed depending on the Mo-film sputtering temperature and pressure. Based on the secondary ion mass spectroscopy, the in-depth profile of Na in the CIGS film is correlated with those of H and O, which depended on the Mo-film sputtering condition and air exposure time. The degradation of the CIGS film in view of PL is discussed in terms of the Na close to the CIGS surface, which reacted with O2 and H2O. CIGS solar cells were examined in relation to Mo sputtering conditions and the SiO2 sodium barrier. The control of Na diffusion was found to be important for both reducing the rate of CIGS film surface degradation and the realization of a CIGS solar cell with a uniform PL intensity image.