Growth of Perovskite Nanorods from PbS Quantum Dots

Abstract

Organolead iodide perovskites, CH₃NH₃PbI₃, have attracted the attention of researchers around the world due to their optical and electrical properties. Their main characteristics include, direct band-gap (1.4 to 3.0 eV), large absorption coefficient in the visible spectrum, long carrier diffusion length and ambipolar charge transport. Aside that, perovskite thin films can be produced with low cost and are compatible with large-scale manufacture. Perovskite thin films have been synthesized mainly by spin-coating technique and thermal evaporation, which can be executed in one or two steps. Aiming to increase the light absorption, nanostructured perovskite thin films are also under intense study, since the nanostructures can absorb more light than a flat film. Thus, in this work, we reported the synthesis of perovskite (CH₃NH₃PbI₃) nanorods by means of conversion of lead sulphide quantum dots (PbSQD). The perovskite nanorods were grown by exposing the PbSQD to a highly concentrated iodine atmosphere and then dipping the resulting film in methylammonium iodide (CH₃NH₃I) solution. The first step converts completely the PbSQD into lead iodide (PbI₂) nanowires, ≈50 μm long and ≈200 nm diameter, through substitution of sulphur by iodine atoms and subsequent aggregation of the particles. The later step converts the PbI₂ nanowires in perovskite nonorods (≈5 μm long and ≈400 nm diameter). The perovskite nanorods present a regular geometry along all its length. A preferential alignment of nanorods to the substrate plane was observed. The preliminary results show that we can control the size of nanorods through exposition time of PbSQD to iodine, which change the size of PbI₂ nanowire as well. The conversion process was studied by x-ray diffraction, optical absorption, photoluminescence and scanning electron microscopy.