Minimizing interfacial energy losses via multifunctional cage-like diammonium molecules for efficient perovskite/silicon tandem solar cells

Wide bandgap (WBG) perovskites hold tremendous potential for enabling efficient perovskite/silicon tandem solar cells. However, interfacial energy losses at the perovskite/electron selective contact interface remain a substantial obstacle in approaching its theoretical efficiency limit. Herein, for the first time, a multifunctional cage-like diammonium chloride molecule, featuring Lewis acid/base groups and strong molecular polarity, is designed to reduce film defects and modulate the interfacial dipole, thereby suppressing non-radiative recombination and optimizing surface band alignment. More importantly, the unique cage-like cation can induce the formation of a phase-pure quasi-2D perovskite with spontaneous in-plane orientation and exhibits a pronounced ferroelectric effect, facilitating carrier further apart and extraction by upshifting the surface work function. Consequently, we achieve 1.68 eV perovskite solar cells with power conversion efficiencies (PCEs) of 22.6% (0.1 cm²) and 21.0% (1.21 cm²). Furthermore, two-terminal monolithic perovskite/silicon tandem solar cells based on tunnel oxide passivating contact yield an impressive PCE of 31.1% (1.0 cm²) and demonstrate a decent operational stability (ISOS-L-1, T₈₅ > 1020 h in ambient conditions without encapsulation). The ferroelectric interface physics opens new possibilities for efficient and stable perovskite-based tandem photovoltaics.