Molecularly tailored quaternary pyridinium salt for post-treatment to enhance defect passivation and charge carrier dynamics in perovskite solar cells

The modification of the perovskite surface using functional additives is one of the most promising strategies to reduce nonradiative recombination and improve the stability of perovskite solar cells (PSCs). In this work, a novel quaternary pyridinium-based halide salt, 1-ethyl-4-(methoxycarbonyl) pyridinium iodide (EMCP-I), is introduced as an effective post-treatment molecule to improve the quality of the perovskite film. EMCP-I exhibits dual functionality to passivate both negatively and positively charged defects and improve the film morphology. Furthermore, the treatment fine-tunes energy level alignment between the perovskite layer and the hole transport layer (HTL), facilitating more efficient charge transport. Consequently, EMCP-I-treated devices achieve a remarkable power conversion efficiency (PCE) improvement from 20.5% to 22.6%, driven primarily by an enhanced open-circuit voltage (V_OC). Beyond efficiency gains, the treatment significantly enhances the environmental and operational stabilities of solar cells. This work provides a guide for tailoring quaternary pyridinium-based molecules for simultaneous improvement of the efficiency and stability of PSCs.