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

Three–terminal tandem solar cells (3T 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, we conduct detailed balance limit calculations for different combinations of top and bottom cell bandgaps to determine the optimum bandgap pairing and limiting efficiency of 3T TSCs. An experimental realisation 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 parametrisation for non–radiative recombination. We further determine 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. To this end, we incorporate non–radiative recombination in our model and quantify it 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 our own best in–house 3T TSC. This article is protected by copyright. All rights reserved.