Dynamic ligand control of crystalline phase and habit in cesium lead halide nanoparticles (1702.05382v1)

Abstract: Active control over the shape, composition and crystalline habit of nanocrystals is a long sought-after goal. Various methods have been shown to enable post-synthesis modification of nanoparticles, including the use of the Kirkendall effect, galvanic replacement and cation or anion exchange, all taking advantage of enhanced solid-state diffusion on the nanoscale. In all these processes, however, alteration of the nanoparticles requires introduction of new precursor materials. Here we show that for cesium lead halide perovskite nanoparticles, a reversible structural and compositional change can be induced at room temperature solely by modification of the ligand composition in solution. Reversible transformation of cubic CsPbX3 nanocrystals to rhombohedral Cs4PbX6 nanocrystals is achieved by controlling the ratio of oleylamine to oleic acid capping molecules. This scheme does not only enable fabrication of high purity monodisperse Cs4PbX6 nanoparticles with controlled sizes. Rather, dependent on the Cs4PbX6 nanoparticles final size afforded by reaction time, the back reaction yields CsPbX3 nanoplatelets with controlled thickness. These results shed some light on the unique properties of this family of materials, provide hints to the origin of their superb photovoltaic performance and point at possible routes for their controlled fabrication and stabilization.