Microstrain and Urbach Energy Relaxation in FAPbI₃-Based Solar Cells through Powder Engineering and Perfluoroalkyl Phosphate Ionic Liquid Additives

Structural and electronic imperfections are the origin of defects and lead to nonradiative recombination that is detrimental to fabricating efficient perovskite solar cells. Here, we propose a powder engineering methodology for α-FAPbI3 as a precursor material. Our developed methodology of α-FAPbI3 synthesis mitigates the notorious structural and electronic imperfections evidenced by a significant decline in the microstrain and Urbach energy as compared to reported δ-FAPbI3 powder and conventional precursor routes. In addition to the performance enhancement in photovoltaics, our engineered powder showed remarkable thermal and moisture stability along with cost-effectiveness through the employment of low-grade PbI2. Further, through additive engineering, with the use of ultrahydrophobic perfluoroalkyl phosphate anion-based ionic liquids, the microstrain and Urbach energy achieved the lowest values of 1.67 × 10–4 and 12.47 meV, respectively, as a result of defect passivation and a semi-ionic F–Pb interaction that stabilizes the surface.