Solvent Dopant-Regulated Grain Formation for Bismuth Iodide Thin-Film Photodetectors.

Simple solution-based processes to generate pinhole-free bismuth iodide (BiI₃) thin films with large, interconnected crystal grains have remained elusive. Here, a survey of the solvent systems for BiI₃ is conducted. Using a novel binary solvent doping approach to carefully regulate the crystallization kinetics, we generate high-quality BiI₃ thin films. Our method circumvents the current requirement for unreliable postprocessing techniques such as solvent vapor annealing or antisolvent dripping. Investigations reveal that 2-methoxyethanol doped with small amounts of N-methyl-2-pyrrolidone (NMP) is the ideal combination of parent and dopant solvent providing high vapor pressure and the intermediate coordination strength necessary to successfully achieve large grain formation in a single step. To evaluate optoelectronic performance, we integrated our optimized thin films into lithographically patterned lateral photodetectors (PDs). Our PD devices show fast millisecond response times, record responsivities of ∼1.61 A/W at moderate device bias (5 V), and excellent sensitivity, with detectivity reaching 1.9 × 10¹² cm Hz^1/2 W^–1 (Jones). The high-quality BiI₃ semiconductor thin films outlined here, coupled with their ease of fabrication, enhance the development of BiI₃ optoelectronic devices and also serve as excellent template films for the fabrication of related bismuth perovskite materials. [ABSTRACT FROM AUTHOR]