Bandgap Pairing in Three‐Terminal Tandem Solar Cells: From Limiting Efficiency to Voltage‐Matched Device Performance

Three‐terminal tandem solar cells (3 T TSCs) have recently sparked increasing interest as they feature a lean monolithic device architecture similar to two‐terminal TSCs and, like four‐terminal TSCs, do not require current matching for optimal operation. In this contribution, detailed balance limit calculations for different combinations of top and bottom cell bandgaps are conducted to determine the optimum bandgap pairing and limiting efficiency of 3T TSCs. An experimental realization of a 3T TSC with perovskite and silicon sub‐cells and a combined efficiency of 28.9% is presented and used to derive a realistic parameterization for non‐radiative recombination. Herein, the optimum bandgap pairing and resulting maximum efficiency under voltage‐matched conditions for voltage‐matching ratios of 1:2 and 2:3, which is relevant for stringing and module integration of 3T TSCs, are further determined. To this end, non‐radiative recombination is incorporated in the model and quantified by matching theoretical open‐circuit voltages and those of real‐world high‐efficiency solar cells based on different absorber materials (and thus bandgaps), including the perovskite top cell of the best in‐house 3T TSC.