Photoluminescence characterization of surface degradation mechanism in Cu(In,Ga)Se₂thin 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)Se 2 (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/SiO 2 (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 O 2 and H 2 O. CIGS solar cells were examined in relation to Mo sputtering conditions and the SiO 2 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.

Effect of potassium fluoride post-deposition treatment on Cu(In,Ga)Se2 thin films and solar cells fabricated onto sodalime glass substrates

“…In solar cells fabricated with KF-PDT, there were remarkable improvements in PL intensity and a decrease in the defect-related PL peaks observed at lower photon energy than that of the near-band edge emission. The PL decay curves of the CIGS solar cells fabricated with and without KF-PDT were well fitted by two exponential decay curves: where I(t) is the time-dependent PL intensity, τ 1 and τ 2 (minority carrier lifetime) are short and long PL lifetimes, respectively, and A 1 and A 2 are the PL intensities of the corresponding PL components [31][32][33][34][35][36][37][38]. The PL lifetime of the CIGS solar cells fabricated with KF-PDT is longer than that of the CIGS solar cells fabricated without KF-PDT.…”

Photoluminescence characterization of Cu(In,Ga)Se2 solar‐cell processes

“…However, there are very few studies on the properties of PL in the photovoltaic heterojunction . The authors have studied a near‐band‐edge (NBE) PL at room temperature in both CIGS thin films and CIGS solar cells . PL in the CIGS solar cell was compared with that in the CIGS thin film .…”

“…PL in the CIGS solar cell was compared with that in the CIGS thin film . Intensity and decay time in the NBE PL in CIGS solar cells are studied . PL intensity ( I PL ) and PL decay time ( τ PL ) in CIGS solar cells are found to be strongly affected by the photovoltage ( V photo ) due to the PL excitation light .…”

“…The two‐dimensional I PL mapping of in the CIGS solar cell demonstrated that the V oc distribution characterized by the PL method is much more sensitive than the light beam‐induced current (LBIC) method . The PL mapping method has been developed as the noncontact characterization of V oc during the solar‐cell process .…”

“…In this article, PL studies in CIGS solar cells are reviewed with emphasis on I PL and τ PL in the photovoltaic heterojunction, characterization of V photo by the PL mapping method, PL in CIGS solar‐cell process , and the degradation of the CIGS surface in air .…”