In Situ Self-Elimination of Defects via Controlled Perovskite Crystallization Dynamics for High-Performance Solar Cells

Understanding and controlling crystallization is crucial for high-quality perovskite films and efficient solar cells. Herein, the issue of defects in formamidinium lead iodide (FAPbI3) formation is addressed, focusing on the role of intermediates. A comprehensive picture of structural and carrier evolution during crystallization is demonstrated using in situ grazing-incidence wide-angle X-ray scattering, ultraviolet-visible spectroscopy and photoluminescence spectroscopy. Three crystallization stages are identified: precursors to the & delta;-FAPbI3 intermediate, then to & alpha;-FAPbI3, where defects spontaneously emerge. A hydrogen-sulfate-based ionic liquid additive is found to enable the phase-conversion pathway of precursors & RARR; solvated intermediates & RARR; & alpha;-FAPbI3, during which the spontaneous generation of & delta;-FAPbI3 can be effectively circumvented. This additive extends the initial growth kinetics and facilitates solvent-FA+ ion exchange, which results in the self-elimination of defects during crystallization. Therefore, the improved crystallization dynamics lead to larger grain sizes and fewer defects within thin films. Ultimately, the improved perovskite crystallization dynamics enable high-performance solar cells, achieving impressive efficiencies of 25.14% at 300 K and 26.12% at 240 K. This breakthrough might open up a new era of application for the emerging perovskite photovoltaic technology to low-temperature environments such as near-space and polar regions. It is found that a hydrogen-sulfate-based ionic liquid additive enables the phase-conversion pathway of precursors & RARR; solvated intermediates & RARR; & alpha;-FAPbI3, which results in the self-elimination of defects during crystallization. The improved perovskite crystallization dynamics finally endow solar cells with high efficiencies of 25.14% at 300 K and 26.12% at 240 K. image