Bromine-functionalized carbazole derivatives in perovskite precursors: defect passivation for enhanced perovskite photovoltaics

-carbazol-9-yl)ethylphosphonic acid (Br-2PACz), were directly incorporated into perovskite precursors to investigate their influence on film formation and electronic structure. Compared with the control film, the incorporation of both 2PACz and Br-2PACz improved film uniformity and morphology, and significantly prolonged carrier lifetimes, indicating suppressed non-radiative recombination and reduced defect density. Notably, Br-2PACz shows a more pronounced effect: the bromine substituent enhances the electron-withdrawing character of the molecule, leading to a deeper highest occupied molecular orbital (HOMO) level and pronounced modulation of the interfacial electronic structure. As a result, the energy-level alignment at the perovskite/electron-transport interface is optimized, facilitating charge extraction and defect passivation. These synergistic effects contribute to higher power conversion efficiency (PCE). This work demonstrates an additive-engineering approach based on carbazole SAMs to control perovskite crystallization and interfacial energetics, providing a promising pathway toward high-efficiency PSCs.