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 BiI(3 )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 similar to 1.61 A/W at moderate device bias (5 V), and excellent sensitivity, with detectivity reaching 1.9 x 10(12) 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.