Bifunctional Modulation of Nucleation and Phase Transformation by TFMBT for Efficient Carbon-Based CsPbI3– x Br x Perovskite Solar Cells

All-inorganic CsPbI3–xBrx perovskites have emerged as promising photovoltaic materials owing to their excellent thermal stability and tunable bandgap. However, solution-processed CsPbI3–xBrx films continue to suffer from sluggish crystallization kinetics and poor phase stability, which severely limit device performance. Herein, we introduce 6-(trifluoromethyl)–2(3H)-benzothiazolethione (TFMBT) as a multifunctional additive to regulate nucleation and phase transformation. The N–H and C=S groups of TFMBT synergistically weaken the DMSO-[PbI6]4– coordination via hydrogen bonding and Lewis acid–base interactions, facilitating solvent removal and lowering the nucleation barrier. Meanwhile, the CF3 group engages the N–H group of DMA+ in N–H···F contacts, accelerating DMA+ deintercalation and Cs+ incorporation to expedite phase transformation. This synergistic effect cooperatively accelerates the crystallization kinetics, yielding high-quality films with enlarged, uniform grains and suppressed defects. Benefiting from the optimized crystallization regulation and improved film quality, the TFMBT-modified carbon-based CsPbI3–xBrx perovskite solar cells achieve a champion power conversion efficiency of 15.34%, significantly outperforming the control devices (12.75%), along with excellent stability.