Consecutive surface matrix engineering of FAPbI3 perovskite quantum dots for solar cells with over 19% efficiency

Formamidinium lead triiodide perovskite quantum dots (FAPbI₃ PQDs) attract increasing attention to new-generation photovoltaics due to their exceptional optoelectronic properties and solution processability. However, the high density of insulating ligands on the PQD surface significantly affects the charge carrier transport in the PQD solids, thus to a large extent dominating the photovoltaic performance of PQD solar cells (PQDSCs). Herein, a consecutive surface matrix engineering (CSME) strategy is reported to promote ligand exchange of the PQDs with diminished surface vacancies. The results reveal that the CSME could disrupt the dynamic equilibrium of the proton exchange between the oleic acid (OA) and oleylamine (OAm) by inducing the amidation reaction between the OA and OAm, which advances insulating ligand desorption from the PQD surface and thus enhances the electronic coupling of PQDs. Meanwhile, during the CSME, the short-chain conjugated ligands with high binding energy to the PQD surface could efficiently occupy the surface vacancies of the PQDs resulting from the insulating ligand desorption, suppressing trap-assisted nonradiative recombination. Consequently, a record high efficiency of up to 19.14% is realized in FAPbI₃ PQDSCs with improved operation stability. This work provides important insights into the design principles of the surface ligand engineering of PQDs with executable approaches for high-performance optoelectronic devices.