Thomas Baier

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 CsPbI ₃ 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 PbI ₂ 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.

By means of Grazing Incidence Small Angle Neutron Scattering under hydrostatic pressure (HP - GISANS) and neutron reflectometry at the solid-liquid interface, we compare effects of pressure and temperature on two model homopolymer mixed brush systems in thin (< 100 nm) film geometry: a weakly incompatible (poly(methylmethacrylate) / poly(2-(dimethylamino)ethyl methacrylate)) (PMMA / PDMAEMA) and strongly incompatible ((poly((2,2,3,3,4,4,5,5-octafluoro)pentyl methacrylate))/ poly(2-(dimethylamino)ethyl methacrylate) ) (POFPMA/PDMAEMA) one. A dual responsive, temperature and pressure-sensitive, polymer (PDMAEMA) in both systems allows to explore the role of mixing incompatibilities between tethered macromolecules with solvent and also pressure on the morphological changes in the PDMAEMA-containing nanostructures. Our findings indicate distinct pressure-dependent response in both lateral (HP-GISANS) and transversal (specular NR) nanostructure depending on the chemical composition. Specular ToF-NR results suggest that temperature effects are found to be counteracted by pressure and also that presumably mixing non-idealities and residual unoccupied volume within the investigated mixed brushes are polymer-compatibility dependent as evidenced by enhanced D2O retention within the brush by the strongly incompatible POFPMA/PDMAEMA mixed brush. GISANS analysis indicates the presence of uncorrelated cylindrical hydrophobic nanostructures within a PDMAEMA-based swollen matrix. Moreover, off-specular scattering (OSS) analysis demonstrates that the spacing between hydrophobic domains and the associated surface coverage exhibits changes with pressure only for the strongly incompatible POFPMA/PDMAEMA mixed brush. Our HP - GISANS and off-specular scattering results suggest that the length scale of phase separation on the sample surface along the beam direction can strongly depend on the compositional variation in the mixed brushes.

Multimodal in situ experiments during slot-die coating of thin films pioneer the way to kinetic studies on thin-film formation. They establish a powerful tool to understand and optimize the formation and properties of thin-film devices, e.g., solar cells, sensors, or LED films. Thin-film research benefits from time-resolved grazing-incidence wide- and small-angle x-ray scattering (GIWAXS/GISAXS) with a sub-second resolution to reveal the evolution of crystal structure, texture, and morphology during the deposition process. Simultaneously investigating optical properties by in situ photoluminescence measurements complements in-depth kinetic studies focusing on a comprehensive understanding of the triangular interdependency of processing, structure, and function for a roll-to-roll compatible, scalable thin-film deposition process. Here, we introduce a modular slot-die coater specially designed for in situ GIWAXS/GISAXS measurements and applicable to various ink systems. With a design for quick assembly, the slot-die coater permits the reproducible and comparable fabrication of thin films in the lab and at the synchrotron using the very same hardware components, as demonstrated in this work by experiments performed at Deutsches Elektronen-Synchrotron (DESY). Simultaneous to GIWAXS/GISAXS, photoluminescence measurements probe optoelectronic properties in situ during thin-film formation. An environmental chamber allows to control the atmosphere inside the coater. Modular construction and lightweight design make the coater mobile, easy to transport, quickly extendable, and adaptable to new beamline environments.