Multi‐Functional Interface Engineering for Monolithic Perovskite/Perovskite/Crystalline Silicon Triple‐Junction Tandem Solar Cells

Perovskite/perovskite/silicon triple-junction tandem solar cells (TSCs) hold significant potential for achieving higher efficiencies while lowering the levelized cost of electricity. The top subcell utilizing wide-bandgap (WBG) perovskite is crucial for improving the efficiency of TSCs. However, the defects caused by poorly crystallized WBG perovskite films and suboptimal energy level alignment lead to significant energy loss. Herein, we present a multifunctional interface engineering utilizing piperazinium bromide (PZBr) for enhancing the property of 2.03-eV perovskite films. The unique molecular structure of PZBr enables it to effectively passivate defects in perovskite films, to suppress photoinduced phase segregation, and to improve the energy band alignment between perovskite films and contact layers. Additionally, the PZBr modification facilitates the crystal ripening process in perovskite polycrystalline films. These functions result in suppressed non-radiative recombination and accelerated carrier extraction. Consequently, single-junction 2.03-eV perovskite solar cells (PSCs) achieved a remarkable efficiency of 13.82%, one of the highest efficiencies reported for PSCs with a bandgap exceeding 2.0 eV. In further, a monolithic triple-junction TSC was fabricated, achieving a photovoltage of 2.96 V and a champion efficiency of 20.05% (aperture area: 1 cm2). This work underscores the critical role of PZBr-based interface engineering in advancing WBG PSCs and triple-junction TSCs.