Managing Grain Boundary Energy by Dipole Strategy in Sn-Pb Perovskite for All-Perovskite Tandems

All-perovskite tandem solar cells (TSCs) offer a path to exceed the Shockley-Queisser limit of single-junction devices, yet their development is hindered by the inferior efficiency and stability of low-bandgap tin-lead (Sn-Pb) perovskite bottom cells. The inherent grain boundaries (GBs) in Sn-Pb perovskites feature detrimental p-type energy states and unfavorable upward energy band bending that promote non-radiative charge recombination and pathways for ion migration-induced degradation. Herein, we employ dipole management at GBs of Sn-Pb perovskite by 4-(trifluoromethyl)benzohydrazide (FBH), which effectively modulates the GB energy landscape throughout the film. The dipole effect reverses the top surface GB energy states to create downward bending of the energy band, promoting efficient charge separation at GBs. Concurrently, FBH treatment enhances perovskite film quality through grain growth regulation, defect passivation, and immobilization of FA⁺/I^- ions. Consequently, the optimized Sn-Pb perovskite solar cell achieves a high efficiency of 23.25% with outstanding operation stability, i.e., keeping over 80% of its initial efficiency under 85°C thermal stress after 400 h and 90% of its original efficiency upon 1872 h in glove box. All-perovskite TSC obtains 29.67% efficiency and retains 90% of its initial efficiency after approximately 1000 h maximum power point tracking.