The impact of the carrier concentration and recombination current on the p+pn CZTS thin film solar cells

Abstract

One of the main causes of low performance of Cu2ZnSnS4 (CZTS) based thin film solar cells is its high recombination current. In this paper, the effects of the carrier concentration and recombination current in the CZTS thin film solar cells have been carefully scrutinized. In continue, for comparison and validation, two simulated structures based on the CZTS absorber layer have been reproduced and the influence of the absorber layer defects and carrier concentration has been analyzed. In this work, two different structures using p+-CZTS intermediate layer (between the CZTS absorber layer and Mo back-contact) and dual CZTS layer have been proposed and optimized to decrease recombination and extract the desired photovoltaic parameters. By using and optimizing these structures as p+pn junction, 15.62% and 19.08% efficiencies have been achieved in p+-CZTS intermediate layer and p+pn CZTS dual layer structures, respectively. The highest efficiency of dual absorber based solar cell is achieved when the carrier concentration of the p+-CZTS and p-CZTS absorber layers is 1 × 1018 cm−3 and 5 × 1015 cm−3, respectively. Moreover, the optimum thickness of the p+-CZTS and p-CZTS absorber layers in p+pn CZTS dual layer structure is 1 and 1.5 µm, respectively. Finally, the total recombination current density is reduced to 2.05 mA/cm2.