Electrical characterization of Cu(In,Ga)Se2-solar cells by voltage dependent time-resolved photoluminescence

Time-resolved photoluminescence (TRPL) is a promising method for the investigation of charge carrier dynamics and recombination kinetics in semiconductor devices. To characterize Cu(In,Ga)Se2 (CIGSe) solar cells, we measured TRPL for different applied external forward voltages. We show that the TRPL decay time increases with increasing voltage in case of a high excitation intensity. This result is valid for a wide range of excitation frequencies of the laser. By simulation of the measured transients we determined semiconductor parameters which allow fitting the experimental photoluminescence transients for different voltages. The deduced quantities are the lifetime for deep defect assisted Schockley-Read-Hall recombination, doping density and charge carrier mobilities of the solar cell's absorber layer with values of 10 ns, 2 × 1015 cm− 3 and 1 cm2 V− 1 s− 1, respectively, for a standard CIGSe solar cell. We further studied the appearance of a photovoltage in TRPL experiments with single-photon-counting methods. By experimental results we show a dependence of the open circuit voltage on the laser repetition rate, which influences the TRPL decay.