Multisite Synergistic Defect Passivation via Pyridine Molecules for High-Efficiency and Stable Perovskite Solar Cells

Abstract

A critical challenge in achieving high-efficiency and stable metal-halide perovskite solar cells (PSCs) is trap-mediated nonradiative charge recombination from charged defects at surfaces and grain boundaries. While molecular passivation strategies have been widely explored, developing a universal passivator capable of simultaneously addressing multiple defect types—such as undercoordinated Pb²⁺, halide vacancies I⁻, and organic cation disorders—remains a significant hurdle. An ideal passivator should incorporate multiple-functional groups that can interact synergistically with diverse defects. In this work, multifunctional pyridine-based molecules have emerged as promising candidates due to their dual role in modulating perovskite crystallization and passivating defects. Notably, 2-mercapto-5-trifluoromethylpyridine (MPTM) exhibits a unique triple-functional passivation mechanism: the thiol and pyridinic nitrogen groups coordinate with undercoordinated Pb²⁺ ions, mitigating deep-level traps; the trifluoromethyl functional group forms hydrogen bonds with FA⁺, suppressing its migration; and in polar solutions, MPTM undergoes isomerization to a zwitterionic thiocarbonyl imide, enabling simultaneous interactions with I⁻ vacancies, FA⁺, and Pb²⁺. This synergistic defect suppression minimizes nonradiative recombination, leading to enhanced charge transport and extraction. As a result, MPTM-passivated devices achieve a champion power conversion efficiency (PCE) of 24.32%. Furthermore, the optimized unencapsulated PSCs demonstrate outstanding environmental stability, retaining >91% of their initial PCE after 66 days in humid air.