In Situ Bonding Regulation of Surface Ligands for Efficient and Stable FAPbI Quantum Dot Solar Cells.

Quantum dots (QDs) of formamidinium lead triiodide (FAPbI ) perovskite hold great potential, outperforming their inorganic counterparts in terms of phase stability and carrier lifetime, for high-performance solar cells. However, the highly dynamic nature of FAPbI QDs, which mainly originates from the proton exchange between oleic acid and oleylamine (OAm) surface ligands, is a key hurdle that impedes the fabrication of high-efficiency solar cells. To tackle such an issue, here, protonated-OAm in situ to strengthen the ligand binding at the surface of FAPbI QDs, which can effectively suppress the defect formation during QD synthesis and purification processes is selectively introduced. In addition, by forming a halide-rich surface environment, the ligand density in a broader range for FAPbI QDs without compromising their structural integrity, which significantly improves their optoelectronic properties can be modulated. As a result, the power conversion efficiency of FAPbI QD solar cells (QDSCs) is enhanced from 7.4% to 13.8%, a record for FAPbI QDSCs. Furthermore, the suppressed proton exchange and reduced surface defects in FAPbI QDs also enhance the stability of QDSCs, which retain 80% of the initial efficiency upon exposure to ambient air for 3000 hours.