Strain‐Induced Intrinsic Constraint Boosts Slow‐Thermalization and Fast‐Transfer of Carriers in FAPbI ₃ Quantum Dot Solar Cells

Abstract

Abstract Formamidinium lead iodide quantum dots (FAPbI 3 QDs) are extensively utilized in photovoltaic applications due to their superior optoelectronic characteristics. Nonetheless, the weak ionic bonds within their soft lattice structure lead to structural deformation, which causes a disordered charge distribution of FAPbI 3 QDs. Stress engineering not only can mitigate the inherent soft lattice by reinforcing ion bonds but also can promote electron localization, thus enhancing charge carrier transfer. This work introduces a strain‐induced intrinsic constraint (SIC) strategy that employs steric bulk modulation of nitrogen‐rich ligands to induce anisotropic surface strain (ɛ = 0.53–0.78) in FAPbI 3 QDs. By systematically designing nitrogen‐coordinating ligands, guanidinium acetate (GA‐acid) is demonstrated to facilitate controlled anisotropic lattice strain by filling A‐site vacancies while simultaneously establishing a self‐reinforcing stress, which effectively strengthens the antibonding interaction of Pb‐O/I and reduces Pb‐Pb orbital overlap, resulting in “slow‐thermalization and fast‐transfer” synergy for enhanced charge transfer. The PQDSCs engineered using the SIC approach achieve a photoelectric conversion efficiency of 17.11% and a highest short‐circuit current density of 20.96 mA·cm −2 . It is anticipated that stress‐induced modulation of nanocrystals offers a critical insight for advancing the photovoltaic performance of perovskite solar cells.