Photonic Intermediate Structures for Perovskite/c-Silicon Four Terminal Tandem Solar Cells

Tandem perovskite/silicon devices are promising candidates for highly efficient and low-cost solar cells. Such tandem solar cells, however, require careful photon management for optimum performance, which can be achieved with intermediate photonic structures. Here, we identify the ideal requirements for such intermediate structures in perovskite/silicon tandem cells. Counter-intuitively, we find that the reflectance in the perovskite absorption window, i.e., below approx. 800 nm wavelength, does not have a strong impact on the tandem performance. Instead, the main function of the intermediate structure is to act as an optical impedance matching layer at the perovskite-silicon interface. This insight affords the design of simple and tolerant photonic structures that can obtain efficiencies surpassing 30%, assuming a passivated emitter, rear locally diffused (PERL) bottom cell and realistic perovskite top cell, by optical impedance matching alone.