In Situ Bonding Regulation of Surface Ligands for Efficient and Stable FAPbI3 Quantum Dot Solar Cells

Abstract Quantum dots (QDs) of formamidinium lead triiodide (FAPbI 3 ) 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 3 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 3 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 3 QDs without compromising their structural integrity, which significantly improves their optoelectronic properties can be modulated. As a result, the power conversion efficiency of FAPbI 3 QD solar cells (QDSCs) is enhanced from 7.4% to 13.8%, a record for FAPbI 3 QDSCs. Furthermore, the suppressed proton exchange and reduced surface defects in FAPbI 3 QDs also enhance the stability of QDSCs, which retain 80% of the initial efficiency upon exposure to ambient air for 3000 hours.