Gas-Phase Anion Exchange for Multisegment Heterostructured CsPb(Br_1-xCl_x) ₃ Perovskite Nanowires

Metal-halide perovskites (MHPs) are promising as active optoelectronic materials for a diverse range of devices. Anion exchange is a post-growth modification of MHP materials that allows tuning of the band gap and crystal structure by exposure to alternative halides, normally using solution methods. Here, low temperature gas-phase anion exchange for the conversion of CsPbBr3 nanowires (NW) into CsPb(Br1-xClx) NWs using two media, fuming HCl and Cl-2 gas, is systematically investigated. It is found that both methods can be used to tune the composition in the full range with excellent control. While fuming HCl is the simplest process, Cl-2 gives similar results with no surface damage and better process control. Based on a simple solid diffusion model, an average diffusivity of 1.4 x 10(-12) cm(2)s(-1) is extracted for Cl-anions inside CsPbBr3. By combining the Cl-2 exchange process with electron-beam lithography patterning, heterojunction NWs with varying halide compositions are produced, including complex barcode-like NWs with segment lengths as short as 500 nm. Designed heterostructures provide an important basis for optoelectronic device applications of MHPs, and gas-phase anion exchange should be suitable for any MHP morphology.