Thin film solar cells based on multinary compound Cu(In,Ga)Se2 show record photovoltaic conversion efficiency approaching 20%. Investigation on defect physics in this compound is crucial for making further progress in the technology. In this work we present the results on photocapacitance (PC) and deep level optical spectroscopy (DLOS) for two types of cells – high efficiency Cu(In,Ga)Se2 cell with about 20% of gallium and pure gallium CuGaSe2 device. We show that PC and DLOS, employed as the techniques complimentary to deep level transient spectroscopy DLTS and admittance spectroscopy, are useful methods in providing information on defect levels in solar cells. In particular they are helpful in diffierentiating between levels belonging to the bulk of absorber and to the interface states. We tentatively assign some of the observed deep levels to InCu or GaCu antisites and Cu interstitials.

A method for defects extraction for a mercury cadmium telluride (MCT) multilayer low-bandgap heterostructure is presented. The N⁺/T/p/T/P⁺/n⁺ epitaxial layer was deposited on a GaAs substrate by a metal-organic chemical vapour deposition (MOCVD). The absorber was optimized for a cut-off wavelength of λ_c = 6 μm at 230 K. Deep-level transient spectroscopy (DLTS) measurements were conducted for the isolated junctions of the N⁺/T/p/T/P⁺/n⁺ heterostructure. Three localised point defects were extracted within the p-type active layer. Two of them were identified as electron traps and one as a hole trap, respectively.