Self-biased photodetector using 2D layered bismuth triiodide (BiI 3 ) prepared using the spin coating method.

Layered bismuth triiodide (BiI 3 ) is a 2D material that has emerged as an ideal choice for optical sensors. Although BiI 3 has been prepared using vacuum-based deposition techniques, there is a dearth of research studies on synthesizing this material using chemical route. The present work uses a facile spin coating method with varying rotation speeds (rpm) to fabricate BiI 3 material thin films for photodetection applications. The structural, optical, and morphological study of BiI 3 thin films prepared at 3000-6000 rpm were investigated. XRD analysis indicates formation of BiI 3 films and revealed that BiI 3 has a rhombohedral crystal structure. FESEM analysis showed that BiI 3 films prepared at different rpm are homogeneous, dense, and free from cracks, flaws, and protrusions. In addition, films show an island-like morphology with grain boundaries having different grain sizes, micro gaps, and the evolution of the granular morphology of BiI 3 particles. The UV spectroscopy and photoluminescence analysis revealed that BiI 3 films strongly absorb light in the visible region of spectra with a high absorption coefficient of ∼10 4 cm -1 , have an optical band gap of ∼1.51 eV. A photodetector was realised using fabricated BiI 3 film obtained at an optimum spin speed of 4000 rpm. It showed rapid rise and decay times of 0.4 s and 0.5 s, a responsivity of ∼100 μA W -1 , external quantum efficiency of 2.1 × 10 -4 %, and detectivity of ∼3.69 × 10 6 Jones at a bias voltage of 0 V. Our results point towards a new direction for layered 2D BiI 3 materials for the application in self-biased photodetectors.