Defect Passivation with 4-(Trifluoromethyl)Aniline for Efficient and Stable FAPbI₃ Quantum Dot Solar Cells

Conventional ligand exchange strategies for FAPbI₃ quantum dots (QDs) rely on polar solvents, which compromise colloidal stability and device performance. Herein, a ligand-mediated defect passivation strategy is proposed, in which 4-(trifluoromethyl)aniline (4-ATFB) is incorporated into the toluene-based solvent system during the purification of FAPbI₃ QDs. The amino group of 4-ATFB coordinates with undercoordinated Pb²⁺ sites to passivate defects and optimize FA⁺ charge distribution, while outward-oriented trifluoromethyl group forms a barrier against moisture. The dual functionality stabilizes the lattice and suppresses defects during the purification process. Moreover, the carrier dynamics are significantly improved with 4-ATFB treatment, attributed to reduced defect density and suppressed trap-mediated losses, leading to enhanced radiative recombination. Consequently, the fabricated FAPbI₃ QDs solar cells with 4-ATFB treatment exhibit a champion power conversion efficiency of 16.33%, representing a significant improvement over the control device (14.99%), together with exceptional operational stability that retains over 80% of the initial efficiency after 25 days of storage in an ambient atmosphere without encapsulation.