Morphology-Controlled Synthesis of Ruddlesden-Popper Nanowires of Monolayered Lead Bromide Perovskite

Layered two-dimensional organic-inorganic hybrid perovskites (OIHPs) are promising materials for light emitting purposes owing to their higher exciton binding energies compared to the three-dimensional lattices. Stacking of the 2D layers into ordered phases such as Ruddlesden-Popper phase with well-formed external morphologies is expected to create nanostructures that will bring in nano-confined optical properties while maintaining the quantum-confined electronic nature of layered perovskite sheets. Coupling band excitons with optical cavity modes, for example, has been exploited in nanowires (NWs) and nanoplatelets of 3D perovskites to enable ultra-small, low-threshold lasers. The cavity-coupled light emission is expected to experience a substantial enhancement if the nanostructures are made of layered 2D perovskite sheets. In this presentation, I will show the morphology-controlled synthesis of NWs of monolayered butylammonium lead bromide, (C₄H₉NH₃)PbBr₄, via chemical vapor deposition (CVD). We have systematically investigated the morphological outcomes with independent growth parameters including source temperatures, reactor pressure, and gas flow rates, which is well-summarized in a morphology phase diagram. Structural, elemental, crystallographic analyses will be presented to validate the quality of our NWs. We have observed a sharp, quantized absorption around 400 nm and strong photoluminescence at 405 nm, an indication of the presence of layered (C₄H₉NH₃)PbBr₄ sheets. I will present time-resolved photoluminescence and variable-temperature measurements to show stronger exciton binding characteristics in NWs of 2D (C₄H₉NH₃)PbBr₄than of 3D CsPbBr3. Lastly, I will share the amplified light emission behaviors of the NWs upon pulsed excitation. Our NWs of layered OIHPs present potential to develop ultra-compact, coherent ultraviolet and visible light sources.