Altantulga Buyan-Arivjikh

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.

Optoelectronic performance, defect density, and thin-film morphology of solution-processable lead halide perovskites are highly dependent on nucleation and growth conditions during processing. Additionally, Cs+ incorporation into the lattice can have benign effects on the thin films, which is challenging for scalable, deposition-friendly solvents such as 2-methoxyethanol or acetonitrile due to their highly limited solubility of Cs-containing salts. To address both issues, we present an interface-engineering approach that utilizes CsPbI3 nanocubes as seed crystals for slot-die coating of FAPbI3. The seeds improve growth-control at the bottom interface and enhance Cs+ incorporation into the active layer lattice. Incidence angle varied grazing-incidence wide-angle X-ray scattering enables depth-resolved structural probing of thin films, revealing increased Cs+ incorporation with increasing film depth. Additionally, morphological parameters, such as thin-film “face-on” orientation and crystallographic texture, are significantly improved in the seeded film. Accordingly, the seeded films exhibit reduced defect density and enhanced charge-carrier separation due to increased structural ordering and Cs+ alloy-induced bandgap tuning across the active layer thickness. Resulting p-i-n photovoltaic devices exhibit superior mean values as well as a narrower spread across short-circuit current density, fill factor, and power conversion efficiency, highlighting the beneficial effects of nanocrystal seeding on active-layer quality and reproducibility.

Understanding how material and defect characteristics govern photoelectrochemical performance is essential for developing efficient and stable photoelectrodes. Although bulk properties are often emphasized, surfaces and interfaces can equally determine activity and stability under operation. Here, we use depth-sensitive characterization to disentangle surface and bulk properties of Ta ₃ N ₅ thin films. By preparing photoelectrodes from TaO _x , TaN _x , and Ta precursors, we systematically vary shallow and deep-level defect concentrations. Structural, compositional, and optoelectronic analyses show that the surfaces consistently exhibit oxygen enrichment, increased structural disorder, and higher deep-level defect densities than the bulk. However, the specific surface structure and its spatial extent depend strongly on precursor chemistry. Ta ₃ N ₅ derived from TaO _x forms an extended, amorphous, oxide-rich surface with fewer deep-level defects, whereas TaN _x and Ta-derived Ta ₃ N ₅ films exhibit thinner, more crystalline surfaces with increased mid-gap defect densities. A brief hydrofluoric acid treatment removes the disordered surface layer, improving crystallinity and hydrophilicity and enhancing photoelectrochemical performance and stability for ferrocyanide oxidation. These results highlight interfacial and defect engineering as routes toward durable, high-efficiency Ta ₃ N ₅ photoelectrodes.

Lead-halide hybrid perovskites (RNH₃PbX₃, X = halide, e.g., Cl, Br, I; R = organic moiety) show promise for next-generation optoelectronic devices due to their simple synthesis routes, strong light absorption, and high photoluminescence quantum yield. However, postsynthetic halide exchange in lead-halide perovskites poses a challenge for the functionality of many perovskite devices. For example, in all-perovskite heterostructures, halide diffusion results in the formation of undesired mixed alloys rather than sharp interfaces required for many optoelectronic applications. To address this issue, we incorporated lysine molecules, one of the 20 common amino acids, into a hybrid perovskite MAPbBr₃ (MA = CH₃NH₃) host and investigated their impact on the host's ability to undergo postsynthetic halide exchange. We immersed lysine-incorporated MAPbBr₃ crystals in solutions containing Cl^- or I^- for varying durations and analyzed subsequent halide exchange-related changes using ion chromatography, high-resolution powder X-ray diffraction, and photoluminescence spectroscopy. Our findings unanimously indicate that incorporated lysine significantly impedes postsynthetic Cl^- and I^- diffusion into bulk MAPbBr₃. Our new bioinspired approach opens a route toward mitigating postsynthetic halide exchange in lead-halide hybrid perovskites and improving the suitability of perovskite devices for optoelectronic applications.

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.