Buried Interface Engineering in Metal-Halide Perovskite/NiO Heterostructures through Direct Observation of Interfacial Reactions

Inverted perovskite solar cells (i-PSCs) employing NiO as a hole transport layer (HTL) have attracted considerable attention owing to their p-type nature, wide bandgap, and low cost. However, Ni3+ species at the NiO surface can deprotonate organic cations and oxidize halide anions, promoting the formation of PbI2-rich interfacial layers that hinder hole extraction and enhance nonradiative recombination. Here, we directly reveal the formation of PbI2 and Pb–O species at the buried perovskite/NiO interface using multiple characterization techniques. Based on these insights, bridging molecular interlayers are introduced on NiO. Devices incorporating Me-4PACz and 3PATAT-C3 exhibit enhanced VOC and FF compared with those employing bare NiO, resulting in champion PCE improvements of 11.5% and 19.9%, respectively. These findings provide direct microscopic evidence of buried interfacial reactions at perovskite/ALD-NiO interfaces and demonstrate an effective strategy to mitigate interfacial degradation, offering important guidelines for the design of stable and high-efficiency i-PSCs.