Defect Passivation of Mesoporous Al2O3-Based Buried Interface for Efficient Inverted Perovskite Solar Cells

Buried interface engineering between the hole transport layer and perovskite remains a critical challenge for inverted perovskite solar cells (IPSCs). Al2O3-based interface modification provides excellent interfacial stability and ion-blocking capability; however, its insulating nature and chemical inertness limit effective carrier transport modulation and defect regulation at the buried interface. Here, a synergistic interface engineering strategy is developed by incorporating phenethylammonium bromide (PEABr) into an ultrathin Al2O3 matrix to construct a multifunctional composite interlayer at the NiOX/perovskite buried interface. The introduced PEABr chemically reconstructs the buried interface through the formation of an interfacial quasi-2D/3D perovskite heterostructure. Bromide species derived from PEABr interact with undercoordinated Pb2+ sites and compensate iodine-vacancy-related defects, while phenethylammonium (PEA+) cations participate in constructing the quasi-2D interfacial phase, which optimizes energy-level alignment and promotes efficient hole extraction across the NiOX/perovskite heterojunction. Moreover, the PEABr-induced quasi-2D/3D interfacial structure improves carrier selectivity and suppresses interfacial recombination, thereby enhancing carrier collection. Electronic characterizations demonstrate that the composite interlayer reduces the charge-transfer resistance from 462.81 to 279.65 kΩ, increases the built-in potential from 0.617 to 0.703 V, and decreases the ideality factor from 2.44 to 1.63, enabling a champion power conversion efficiency of 21.34% for IPSCs. This work provides a feasible strategy for constructing multifunctional oxide-based buried interfaces through simultaneous defect regulation, energy-level optimization, and efficient carrier extraction.