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

Abstract 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 Pb 2+ 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 cm 2 ), and wide‐bandgap (1.73 eV) devices, respectively. Meanwhile, the unencapsulated devices exhibit excellent stability after long‐term storage, thermal‐aging, or light‐soaking.