Hierarchically ordered, narrow-bandgap Bi13S18Br2 nanorod superstructures synthesized via template-guided topotactic transformation

Abstract

Herein, we describe the templated synthesis of near-Infrared (NIR) Bi₁₃S₁₈Br₂ superstructures composed of hierarchically ordered nanorod (NR) networks formed via topotactic transformation. The reaction was performed over two steps in a single batch. First, BiOBr templates were synthesized from BiBr₃ precursors via a heat-up process. Through the delayed hot-injection of elemental sulfur, these chemical templates were topotactically transformed into highly uniform Bi₁₃S₁₈Br₂ nanoframes with orthogonally ordered NR networks. The orthogonal networks of NRs are attributed to preferential growth along the crystallographic orientation of the BiOBr templates. By modulating the morphology of the BiOBr templates, diverse superstructures, such as nanoframes, woodpiles, and multipods, were synthesized while maintaining size and structural uniformity. The colloidal Bi₁₃S₁₈Br₂ superstructures exhibited NIR absorption properties, with an indirect bandgap of 0.80 eV. Owing to their colloidal stability and solution processability, NIR-active photoconductors were fabricated via solution-based deposition followed by a ligand exchange process under ambient conditions. The photoresponsive properties of the Bi₁₃S₁₈Br₂ photodetectors, which exhibited characteristic NIR responsivity under 980-nm illumination, were investigated. Because the proposed reaction can be conducted in a single batch, it can be easily scaled up for mass production. This approach holds considerable potential to facilitate the fabrication of toxic-metal-free, NIR-responsive semiconductors for emerging optoelectronic applications.