Fig. 1

 A schematic illustration of a the n-i-p (left), p-i-n (right) structure, and b mechanically stacked 4-T (left), monolithic 2-T (right) TSCs. Theoretical efficiency limit c for 2-T and d for 4-T tandems, calculated with different bandgap combination. The black dahsed line marks a bandgap of Si. The white dashed line marks the lowest bandgap of perovskite materials. Grey shading region indicates no efficiency gain by tandem cells. Reproduced with permission [79]. Copyright 2018, Springer Nature