Inverse Temperature Crystallization for Inch-Scale, Phase-Pure Ruddlesden-Popper Perovskite Single Crystals

Ruddlesden-Popper perovskites (RPP), a two-dimensional organic-inorganic hybrid perovskites, have emerged as a material class for next generation opto-electronic applications, due to defect-tolerance, solution process, band-gap engineering, and higher chemical stability compared to the three-dimensional perovskite. In particular, RPPs have shown a wider bandgap range (2 to 3 eV) than that of typical 2D transition metal dichalcogenides by controlling the number (<i>n</i>) of inorganic PbX₆ octahedron slabs between ligand layers, which is suitable for light-emitting device applications. While 2D materials are typically tolerant to surface defects, domain boundaries of RPP have been reported to possess a high degree of deep trap states. Therefore, various synthesis techniques including antisolvent vapor assisted crystallization, inverse temperature crystallization, and cation intercalation into pre-existing crystal have been developed to fabricate a large scale and high-quality RPP single-crystals. Although fabricated crystals by conventional methods have single domain in lateral direction, the crystals often contain stacks with different n values which can be considered as impurity phases.<br/>In this contribution, we develop a synthesis process for inch-scale, phase-pure RPP single crystals based on the inverse temperature crystallization technique. Nucleation and crystal growth mechanism are investigated to minimize the impurity phase formation. Various types of RPP single crystals including PEA₂PbBr₄, PEA₂MAPb₂Br₇, PEA₂PbI₄, PEA₂MAB₂I₇, and PEA₂MA₂Pb₃I₁₀ are successfully fabricated using the designed crystallization method with a lateral crystal size of inch scale. The opto-electronic properties of fabricated RPP crystals are characterized via time-resolved photoluminescence spectroscopy and conductive atomic force microscopy. Grazing incident wide angle X-ray scattering measurement is carried out to characterize the strain in RPP layers as well as crystallographic properties. Furthermore, phase purity of the crystal as well as the pico-second scale carrier dynamics are characterized by the transient absorption spectroscopy, demonstrating a potential towards emerging opto-electronic applications.