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

Abstract

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.

All-blade-coated flexible perovskite solar cells & modules processed in air from a sustainable dimethyl sulfoxide (DMSO)-based solvent system

“…Furthermore, LP helped to eliminate the d-FAPI peak at 11.9°and there is no evidence of other major peaks of d-FAPI. 62 The peaks of cubic FAPI and CsPbI 3 at 13.9°and 13.2°are visible in the optimally dried perovskite, which proves the presence of the perovskite phase.…”

Probing proton diffusion as a guide to environmental stability in powder-engineered FAPbI3 and CsFAPbI3 perovskites

“…Though reports appear to suggest a performance enhancement in powder-engineered FAPbI 3 PSCs, 14 , 30 , 31 , 32 the reason for intrinsic stability remains undiscovered to an extent. While comparing the conventional and powder engineering methods, we speculate that the precursor solution step acts as a Y junction in the perovskite fabrication process, and their investigations are crucial.…”

“…We show this is a particularly suitable technique to allow direct probing of local environmental effects, such as relative humidity, on the migration of hydrogen species. Additionally, we have opted for powder-engineered perovskites as the choice of material owing to them (1) achieving the highest PCEs and reproducibility over their conventional counterpart 30 , 31 , 32 and (2) reducing the microstrain and Urbach energy values for perovskite layers fabricated from the powder engineering process, indicating mitigated structural and electronic disorders. 32 Additionally, the powder methodology would overcome the Pb impurities issue from the Pb precursors and eliminate the error in the weighing of the precursors.…”

“…Additionally, we have opted for powder-engineered perovskites as the choice of material owing to them (1) achieving the highest PCEs and reproducibility over their conventional counterpart 30 , 31 , 32 and (2) reducing the microstrain and Urbach energy values for perovskite layers fabricated from the powder engineering process, indicating mitigated structural and electronic disorders. 32 Additionally, the powder methodology would overcome the Pb impurities issue from the Pb precursors and eliminate the error in the weighing of the precursors. The indirect assessment of the moisture protection by surface modification of the powder-engineered α-FAPbI 3 and α-CsFAPbI 3 is obtained by simply monitoring the rate of hydrogen exchange within the active layer in the presence of ambient moisture.…”

Molecular design for perovskite solar cells

“…The halide perovskite precursor solutions are rich in tunable organic molecules, including the precursors, the additives, and the solvent molecules; these are all closely related to the coordination chemistry of the functional molecules and strongly affect the resulting perovskite film quality. Many efforts have been devoted to modifying the precursor solution, additives, and solvents, such as on those for FAPbI 3 preparation, 56‐58 additive MACl, 59‐62 ionic liquid, 63‐65 and MAPbBr 3 quantum dots 66‐68 . For example, the AX and BX 2 precursors in the precursor solution are essentially in the molecular form at the starting point, and non‐stoichiometric precursors are viable to generate improved perovskite film quality; the unreacted PbI 2 is suggested to improve the perovskite film crystallinity 69‐71 and facilitate the electron transfer to the neighboring TiO 2 layer.…”