Shape-, Size-, and Composition-Controlled Thallium Lead Halide Perovskite Nanowires and Nanocrystals with Tunable Band Gaps

Perovskite nanocrystals have shown themselves to be useful for both absorption- and emission-based applications, including solar cells, photodetectors, and LEDs. Here we present a new class of size-, composition-, and shape-tunable nanocrystals made from Tl3PbX5 (X= Cl, Br, I). These can be synthesized via colloidal methods to produce faceted spheroidal nanocrystals, and perovskite TlPbI3 nanowires. Crystal structures for the orthorhombic and tetragonal phase materials, for both pure and mixed halide species, are compared to the literature and also calculated from first-principles in VASP. We show the ability to tune the band gap by halide substitution to create materials that can absorb strongly between 250 and 450 nm. In addition, we show evidence of the confinement effect in pure halide Tl3PbBr5 nanocrystals suggesting size-tuning is possible as well. By tuning the band gap we can create materials with specific absorption spectra suitable for photodetection that display conduction and photoresponse properties similar to previously observed perovskite nanocrystals. We also observe weak emission consistent with indirect band-gap materials. Finally, we are able to demonstrate shape control in these materials, to give some insight into observable phase changes with varying reaction conditions, and to demonstrate the utility of the TlPbI3 perovskite nanowires as wide-band-gap photoconductors. These novel perovskite nanocrystalline materials can be expected to find applications in photodetectors, X-ray detectors, and piezoelectrics.