Theoretical analysis of CZTS/CZTSSe tandem solar cell

Kesterite Cu2ZnSn(SxSe1−x)4 has tunable band-gap values in the range 1 to 1.5 eV depending upon the Sulphur/Selenium stoichiometry. We analyze the proposed tandem configuration of kesterite absorber family using SCAPS-1D for device performance. Pure sulphide kesterite Cu2ZnSnS4 (CZTS) of bandgap 1.5 eV is utilized as top cell and a sulpho-selenide Cu2ZnSn(SxSe1−x)4 (CZTSSe) of band-gap 1.1 eV as the bottom cell stacked in a tandem configuration. We utilize the script file capability of SCAPS to simulate the effect of the presence of the top cell on the bottom cell; as the incident spectrum passes though the top cell, a portion of the incident spectrum is filtered out before it reaches the bottom cell. The condition of identical short circuit current (JSC) in the two cells in the tandem is attained by device optimization. We observe that a conservative estimate of two-junction tandem configuration of CZTS could achieve a minimum efficiency of 15%. This study brings out the device configuration of thin film CZTS/CZTSSe multi-junction for enhancing the efficiency of earth abundant CZTS based solar cells.