Tailoring\nSurface Chemistry of CsPbI<sub>3</sub> Perovskite\nQuantum Dots Using Multifunctional Ligand Enables Efficient and Stable\nSolar Cells

All-inorganic\nCsPbI<sub>3</sub> perovskite quantum dots\n(PQDs)\nhave emerged as promising lighting absorptions for solar cells due\nto their extraordinary optoelectronic properties and good solution-processability.\nHowever, the insulated and dynamic binding characteristics of long-chain\nligands on the CsPbI<sub>3</sub> PQD surface still challenge their\nphotovoltaic efficiency and stability. Herein, an effective solution-ligand-exchange\nstrategy is developed to modify the surface chemistry of the CsPbI<sub>3</sub> PQD utilizing 5-aminopyridine-3-carboxylic acid (5A-3C) during\nthe purification process. Systematic analyses reveal that 5A-3C serves\nas the multifunctional short-chain ligand to exchange long-chain ligands\nand is strongly bonded to the CsPbI<sub>3</sub> PQD surface, thus\nfacilitating the electronic coupling between neighboring PQDs to promote\ncarrier transport ability. Meanwhile, 5A-3C reduced vacancy defects\nof the PQD surface and suppressed carrier nonradiation recombination\nin solar cells. Accordingly, the CsPbI<sub>3</sub> PQD solar cells\nwith 5A-3C treatment exhibit a champion power conversion efficiency\n(PCE) of 15.03%, significantly higher than that of the control device\n(13.45%). The operation stability of unencapsulated devices has also\nbeen significantly improved. This work offers a deep understanding\nof PQD surface chemistry and provides a feasible avenue to realize\nhigh-performance PQD solar cells.