Proposition and computational analysis of a kesterite/kesterite tandem solar cell with enhanced efficiency

Abstract

We propose a dual junction Cu₂ZnSnS₄/Cu₂ZnSnSe₄ (kesterite/kesterite) based tandem configuration and analyze its prospect and viability as a solar cell. Cu₂ZnSnS₄ and Cu₂ZnSnSe₄, both having the kesterite crystal structure, are used as the main absorbers for the top and bottom of cells, respectively. We optimize the thickness of the absorbers using optoelectronic simulations and investigate the effect of absorber thickness on short circuit current density and open circuit voltage. The optimized thicknesses for peak efficiency are found to be 200 nm and 850 nm for Cu₂ZnSnS₄ and Cu₂ZnSnSe₄, respectively. The maximum efficiency of the tandem cell is estimated to be 19.87% including recombination effects such as Shockley–Read–Hall (SRH) and radiative recombination mechanisms. We also investigate the effect of band gap on the performance of the tandem cell and show that a 21.74% efficient tandem cell can be achieved for optimized band gaps. Finally, we report that efficiency could be further enhanced by replacing the CdS buffer layer with eco-friendly ZnS buffer layer and optimizing the tandem structure. The proposition and computational analysis presented in this work may help in achieving higher efficiency kesterite solar cells.