2, Rensselaer Polytechnic Institute, Troy, New York, United States
3, Florida State University, Tallahassee, Florida, United States
4, Rensselaer Polytechnic Institute, Troy, New York, United States
Two-dimensinal van der Waals perovksites (RNH3)2PbX4 are self-assembled by alternating layers of inorganic lead halide and organic ligands. Due to reduced screening from organic layers, the exciton confined in inorganic lead halide layers show binding energy of several hundred meV. The highly stable excitons, along with direct bandgap nature, render (RNH3)2PbX4 an ideal candidate for exciton or polariton studies. While most of these materials/devices were synthesized/fabricated from solution methods, vapor-based synthesis are still needed to minimize impurity and defects. In this work, the vapor-phase growth of single crystalline (C4H9NH3)2PbI4 flakes with high optical quality is reported. Individual single crystalline domains with lateral size about 5-10 µm and thickness 15-100 nm were deposited on Si, SiO2/Si or muscovite mica, showing well-defined rectangular shape. Epitaxial relation were observed between perovskite flakes and mica/Si substrates. Due to the substrate effect therein, the structural phase transition at around 240 K were hindered and room-temperature phase were stabilized till liquid nitrogen temperature. Room temperature photoluminescence (PL) showed full width at half maximum (FWHM) of 70 meV and decay lifetime of several nanoseconds, indicating comparably high quality with mechanically exfoliated counterparts. Based on temperature dependent PL intensity, exciton binding energy 279 ± 46 meV and electron–phonon coupling (Fröhlich) strength around 20 meV are revealed. This vacuum-based method showed better controllability over thickness and structure, and may provide a solution for integrating layered perovskites into optoelectronic devices and systems.