Bifunctional interface engineering for stable perovskite photovoltaics: Synergistic crystallization and defect passivation with a pyridine-3,5-dicarboxylic acid interlayer

In inorganic perovskite solar cells (IPSCs), interfacial stability and defect passivation remain key challenges for achieving higher photovoltaic performance. Here, we propose a buried interfacial molecular engineering strategy using pyridine-3,5-dicarboxylic acid (PDC) as a bifunctional passivator to simultaneously improve crystallinity and suppress defects. The carboxylic groups of PDC chemically anchor onto the TiO 2 surface through esterification with surface hydroxyls, forming a robust interfacial layer, while the nitrogen atom in the pyridine ring coordinates with undercoordinated Pb 2+ ions in the perovskite absorber. This dual interaction effectively passivates defects on both TiO 2 and perovskite surfaces, facilitating efficient electron extraction, improving film crystallinity, and suppressing nonradiative recombination. As a result, the PDC-modified devices deliver a significantly enhanced power conversion efficiency of 14.05%, compared to 9.81% for the control devices, representing an improvement of over 43% under standard AM 1.5G illumination. In addition, the PDC-treated devices exhibit markedly improved environmental and mechanical stability, retaining approximately 90% of their initial efficiency after 500 h of continuous operation without encapsulation. This work demonstrates an effective interfacial molecular engineering strategy for simultaneously boosting efficiency and long-term stability in inorganic perovskite solar cells.