Strain-Induced Intrinsic Constraint Boosts Slow-Thermalization and Fast-Transfer of Carriers in FAPbI₃ Quantum Dot Solar Cells.

Abstract

Formamidinium lead iodide quantum dots (FAPbI₃ 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 FAPbI₃ 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 FAPbI₃ 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.