Tailoring Low-Miller-Index Crystal Facets Realizes Perovskite Solar Cells with Flat Grain-boundary Grooves

Charge transport and nonradiative recombination loss at the buried interface are important factors, which limit the efficiency and stability of perovskite solar cells (PSCs). Herein, we screen a series of diphosphate Lewis-base molecules, where N,N-bis(diphenylphosphino)amine (N-DPPM) with appropriate alkyl chains and multiple active sites not only can efficiently facilitate carrier transport but also coordinate with undercoordinated Pb²⁺ and interact with FA⁺ through N⋯H bond. These features prompt the formation of high-quality perovskite films along (100)/(200) crystal facets. Interestingly, these oriented low-Miller-index crystal facets have approximately a twice-increase in heterointerface energy and twice-decrease in grain-boundary energy, flattening grain-boundary grooves, thereby reducing nanoscale physical voids and releasing residual stress. Consequently, the champion inverted PSCs exhibit impressive power conversion efficiencies of 26.80%, 26.18%, and 20.59% for narrow-bandgap (1.55 eV), large-area (0.5 cm²), and wide-bandgap (1.73 eV) devices, respectively. Meanwhile, the unencapsulated devices exhibit excellent stability after long-term storage, thermal-aging, or light-soaking.