Tailoring Surface Chemistry of CsPbI₃ Perovskite Quantum Dots Using Multifunctional Ligand Enables Efficient and Stable Solar Cells

All-inorganic CsPbI3 perovskite quantum dots (PQDs) have emerged as promising lighting absorptions for solar cells due to their extraordinary optoelectronic properties and good solution-processability. However, the insulated and dynamic binding characteristics of long-chain ligands on the CsPbI3 PQD surface still challenge their photovoltaic efficiency and stability. Herein, an effective solution-ligand-exchange strategy is developed to modify the surface chemistry of the CsPbI3 PQD utilizing 5-aminopyridine-3-carboxylic acid (5A-3C) during the purification process. Systematic analyses reveal that 5A-3C serves as the multifunctional short-chain ligand to exchange long-chain ligands and is strongly bonded to the CsPbI3 PQD surface, thus facilitating the electronic coupling between neighboring PQDs to promote carrier transport ability. Meanwhile, 5A-3C reduced vacancy defects of the PQD surface and suppressed carrier nonradiation recombination in solar cells. Accordingly, the CsPbI3 PQD solar cells with 5A-3C treatment exhibit a champion power conversion efficiency (PCE) of 15.03%, significantly higher than that of the control device (13.45%). The operation stability of unencapsulated devices has also been significantly improved. This work offers a deep understanding of PQD surface chemistry and provides a feasible avenue to realize high-performance PQD solar cells.