In Situ Reaction-Induced Surface Lattice Strengthening of CsxFA1–xPbI3 Perovskite Quantum Dots for Solar Cells with 18.55% Efficiency

Cesium-formamidinium lead triiodide perovskite quantum dots (Cs_xFA_1–xPbI₃ PQDs) exhibit great potential for next-generation photovoltaics, but the formamidinium (FA⁺) cations at the surface lattice of PQDs suffer from dissociation from the surface lattice due to weak binding strength, markedly deteriorating the optoelectronic performance and stability of PQDs. Herein, 2-(aminomethyl)pyridine (2-PyMA) is screened out to in situ react with the surface FA⁺ cation, forming the N-(2-methylpyridine)formamidinium (2-MPyFA⁺) cation. The in situ formed 2-MPyFA⁺ cation robustly anchors on the surface lattice of PQDs as functional ligands, which substantially suppresses the formation of surface lattice vacancies, resulting in PQDs with enhanced optoelectronic performance and stability being obtained. Additionally, PQDs also exhibit high orientation in PQD solids with enhanced electronic coupling, facilitating charge carrier transport between adjacent PQDs. Consequently, PQD solar cells yield an efficiency of up to 18.55%, representing the highest efficiency for Cs_xFA_1–xPbI₃ PQD solar cells. This study demonstrates valuable insights into the chemical design principles of surface ligands with executable approaches to realizing high-efficiency solar cells or other emerging optoelectronic devices.