Theoretical studies of single and tandem Cu2ZnSn(S/Se)4 junction solar cells for enhanced efficiency

We simulated photovoltaic characteristics of single heterojunction solar cell with Cu2ZnSnS4 and Cu2ZnSnS4 absorber layer numerically using one dimensional solar cell capacitance simulator (SCAPS-1D). n-CdS/ZnO double buffer layer is used for hetrostructure interfaces with the absorber layer. The cell performance is investigated against variation of different material layer properties such as thickness, carrier concentration, and defect density. First, the performance is optimized for the single junction solar cell with Mo as back contact material with ' similar to 5 eV work function. A double junction CZTS/CZTSe tandem cell structure is realized keeping the same material properties as is used in the single CZTS and CZTSe solar cell simulation and flat band condition is considered at the interface for efficient carrier transport under matching current conditions. Tandem cell performance is determined after matching the current condition for top and bottom sub-cells. The CZTS/CZTSe short circuit current density is similar to 20.98 mA/cm(2) for current matched 211.33 nm thick CZTS top cell in conjunction with 2000 nm bottom cell. The maximum efficiency obtained under the flat band condition at the contact is similar to 21.7% with open circuit voltage similar to 1.324 V.