Revealing Performance-Limiting Buried Interfaces in Layered Dion–Jacobson Lead–Iodide Perovskites

Dion-Jacobson (DJ) two-dimensional (2D) perovskites have emerged as promising photovoltaic materials due to their superior structural and chemical stability compared to three-dimensional (3D) perovskites. However, their optoelectronic performance remains limited by imperfections at interfaces and a fundamental understanding of these interfacial properties is missing. Herein, we present interfacial structure-property relationships in DJ perovskites by directly probing buried interfaces using combined spectroscopic and microscopic characterization techniques. Multiscale heterogeneities, including phase polydispersity, structural disorder, and nonemissive domains, are more concentrated at buried interfaces than at the top surfaces, limiting overall photophysical performance. A sulfate-based inner-sphere complexation strategy is exploited to homogenize crystal growth and passivate crystal termination, specifically at buried interfaces. This approach suppresses nonradiative recombination and promotes ultrafast interphase carrier transfer within DJ perovskite films. DJ perovskite solar cells achieve a record power conversion efficiency of 20.7% while exhibiting improved environmental stability relative to their 3D counterparts. These findings establish the critical link between the buried interface heterogeneity and the optoelectronic performance of DJ 2D perovskites.