Balancing Crystallization Kinetics and Lattice Strain Enables Thermally Stable Slot-Die-Coated Narrow-Bandgap Perovskite Solar Cells.

Unbalanced crystallization kinetics in mixed Sn-Pb perovskite cause film heterogeneity and high defect densities, thereby constraining overall performance and stability, particularly under scalable processing conditions. Here, we investigate nanocrystal-mediated crystallization regulation in ambient-processed, slot-die-coated narrow-bandgap Sn-Pb perovskites by combining CsPbI3 nanocrystal-assisted processing with time-resolved in situ grazing-incidence wide-angle X-ray scattering (GIWAXS). After nine ISOS-T-3 thermal cycles, the perovskite solar cells (PSCs) fabricated from seeded perovskite films retain 80% of their initial efficiency at 25°C. Operando GIWAXS reveals differences in lattice evolution, residual PbI2 formation, and microstrain accumulation between the control and nanocrystal-assisted films. By linking scalable processing and crystallization kinetics to the subsequent lattice response under thermal cycling, this work establishes a processing, crystallization, structure, stability relationship for narrow-bandgap Sn-Pb perovskites and highlights the importance of controlling early-stage film formation for thermally robust, scalable perovskite photovoltaics.