Graded band gap structure of kesterite material using bilayer of CZTS and CZTSe for enhanced performance: A numerical approach

Abstract

Thin film solar cells based on Cu2ZnSn(S,Se)4 are very promising, because they contain earth abundant elements and show high absorptive behavior. However, the performance of these solar cells are limited and needs to be improved in order to reach efficiencies as high as that reported for Cu(In,Ga)Se2 and CdTe based solar cells. To obtain enhanced performance, the present study investigates the output effect of fixed bilayer CZTS/CZTSe structure with band gap 1.5 and 0.9 eV respectively and the effect of MoS2 interfacial layer between CZTS and CZTSe layer to avoid unintentional elemental diffusion. The idea of bilayer CZTS/CZTSe and CZTS/MoS2/CZTSe structure was exploited to achieve higher open circuit voltage and efficiency by band engineering mechanism compared to single layer. In this numerical study the focus is given to fixed band gap model as the structure is practically feasible to realize with the associated materials. The thin interfacial layer introduced between the two layers ultimately diminishes the recombination process due to the back induced electric field. Finally, the fixed bandgap CZTS/MoS2/CZTSe exhibits better performance with open circuit voltage of 0.88 V and efficiency of 21.1%.