Optical parameters of Cu(In,Ga)Se <sub>2</sub> thin films in polyimide-based solar cells
The structure and optical properties of Cu(In,Ga)Se 2 thin films and cells deposited on Mo­coated polyimide at temperatures 430 and 450 °C are studied by the experimental techniques. The band gap energy E g of the Cu(In,Ga)Se 2 thin films at 4.2 K is determined by employing photoluminescence excitation spectroscopy. The spectral positions of the photoluminescence bands are about 190 - 270 meV below the band gap of E g. Such spectral positions and excitation power dependences of the band suggest that these bands have a deep donor­acceptor (DA) recombination nature influenced by a strong spatially fluctuating potential. The most likely defects, involved in the DA recombination, are the Cu vacancy (V Cu) as acceptors and the Se vacancy (V Se) or In Cu substitutional defects as donors.