Scalable growth of lead-free single-crystalline CsAg2I3 perovskite microribbons with 1D electronic structure: Insights from experiment and DFT

Abstract

Recently, lead-free metal-halide materials have emerged as promising alternatives to traditional lead-based perovskites, offering superior optoelectronic properties while addressing concerns related to toxicity. Among these, ternary copper halides (TCHs) stand out due to their structural diversity, ease of synthesis, excellent optoelectronic characteristics, high abundance, and low cost. Despite the promising properties of TCHs, recent reports have highlighted the instability of Cu⁺ ions, which can readily oxidize to Cu²⁺. This instability poses challenges for the long-term stability and performance of TCH-based materials. Ag halides are a promising alternative due to the inherent stability of Ag⁺ ions. Herein, we report for the first time the successful large-scale synthesis of high-quality single-crystalline CsAg₂I₃ microribbons (MRs) using a novel saturated vapor-assisted crystallization (SVAC) method. The resulting MRs exhibit uniform morphology, smooth surfaces, and well-defined rectangular crystal facets. The MRs show a pure orthorhombic phase with strong preferential growth along the [110] direction. Additionally, strong electron–phonon coupling has been observed through a characteristic I-Ag-I vibrational mode at 111 cm^-1. Compositional homogeneity and chemical states of the CsAg₂I₃ MRs have also been confirmed. The step-by-step growth mechanism of the microribbons is elucidated, where controlled anti-solvent vapor diffusion and solvent evaporation drive nucleation at the droplet periphery, leading to self-assembled aggregates that evolve into uniform MRs. The MRs show strong UV absorption with a bandgap of 3.35 eV and a distinct PL emission at 595 nm, which is attributed to self-trapped excitons (STEs). Notably, CsAg₂I₃ MR demonstrates remarkable environmental stability, maintaining its structural, chemical, and morphological properties even after approximately 45 days of air exposure. DFT calculations reveal a unique 1D chain structure, with Ag-I tetrahedral chains isolated by Cs atoms. Strong covalent Ag-I bonds and highly dispersive bands along the [010] direction are observed, resulting in efficient charge transport and plasmonic excitations. It further enhances the material’s potential for UV sensing and other optoelectronic applications. Overall, the large-scale growth of CsAg₂I₃ MRs, combined with the remarkable stability and favorable optical and electronic properties, establishes CsAg₂I₃ as a highly promising candidate for next-generation high-performance optoelectronic devices, particularly in UV sensing and detection.