Towards a high efficient Cd-free double CZTS layers kesterite solar cell using an optimized interface band alignment

In this paper, we suggest a potential high efficiency Kesterite solar cell with double CZTS layers including efficient band offset alignment. Several loss processes like radiative recombination, existence of defect and traps densities in bulk CZTS and interface CdS/CZTS are considered in the modeling framework. The prediction capability of the adopted modeling framework is assessed with respect to experimental results where a good matching can be distinguished. An optimal solar cell design is investigated by studying the effect of interfacial traps, beside doping and thickness of different device layers. In order to circumvent the CdS/CZTS interface drawback, several window Cd-free materials such as IGZO, TiO2, ZnO, WS2, ZnS are scrutinized. Our findings show that ZnO with high optical and electrical characteristics can significantly boost the solar cell performance. Moreover, in order to tune the band alignment at ZnO/CZTS interface, we explore an appropriate electron affinity of ZnO by varying Mg content where we find that pristine ZnO with (chi = 4.13 eV) establish an optimal band offset with a spike like conformation. The achieved results prove the efficiency of the proposed design in mitigating the unwanted effect of the recombination. By comparing these outcomes with the conventional device efficiency 8.8%, we achieved an enhanced efficiency of 10.68%. The proposed structure may provide advantages such as enhanced absorption behavior and decreased recombination effects.