Efficiency evaluation on Csx[NH2CH = NH2]1−xPb(I1−yBry)3/crystalline silicon tandem solar cells

Compared with the conventional organic cation lead halide perovskite, the mixed-cation lead mixed-halide perovskite CsxFA1−xPb(I1−yBry)3 (FA: NH2CH = NH2) possesses a much better stability thanks to the substitutions of Cs for FA, and Br for I. Moreover, its band gap, Eg, can be tuned in a wide range to meet the request of a high efficient tandem solar cell (TSC) with it as a subcell material. In this work, efficiencies for the four-terminal CsxFA1−xPb(I1−yBry)3/c-Si TSCs are theoretically investigated. Herein, Eg of CsxFA1−xPb(I1−yBry)3 is adjusted approaching 1.75 eV, which is the optimal Eg of top cell material for the TSC with c-Si as the bottom cell. By means of density functional calculations, three sets of x and y for CsxFA1−xPb(I1−yBry)3, which have Eg around 1.75 eV, are obtained. And their refractive indices and extinction coefficients, are also calculated. With the thickness of perovskite top cell, d1, changing from 100 nm to 10 μm, the highest efficiencies of the three sets of CsxFA1−xPb(I1−yBry)3/c-Si TSCs and the corresponding thicknesses of c-Si bottom cell, d2, are studied. For the top cell, radiative recombination is considered. For the bottom cell, Auger recombination is also taken into account. Besides, the radiation coupling effect between two subcells is included. It is found that the Cs0.11FA0.89Pb(I0.56Br0.44)3/c-Si TSCs achieve the highest efficiency among the three sets of TSCs with the same d1. With a 500-nm-thick Cs0.11FA0.89Pb(I0.56Br0.44)3 top cell, the highest efficiency of the Cs0.11FA0.89Pb(I0.56Br0.44)3/c-Si TSC reaches 35.5% when d2 is 160 μm. In an extreme situation, when the thickness of the Cs0.11FA0.89Pb(I0.56Br0.44)3 top cell is 10 μm, the highest efficiency of the TSC is 40.0% and d2 is 190 μm.