Sulfur‐Assisted One‐Pot Synthesis of Ultrathin Rhombus‐Shaped Bi ₂ S ₃ Nanosheets for Flexible NIR Photodetectors

Abstract A sulfur‐assisted one‐pot strategy is developed to synthesize ultrathin bismuth sulfide (Bi ₂ S ₃ ) nanosheets, enabling high‐performance flexible photodetectors. By tuning the sulfur content, the resulting morphology can be controlled to yield either bulk structures or nanosheets. The synthesized Bi ₂ S ₃ nanosheets exhibit a uniform thickness of ≈86 nm and a narrow bandgap of 1.24 eV, enabling broadband light absorption from the ultraviolet (UV) to the infrared (IR) regions. A flexible photodetector is fabricated by uniformly spray‐coating the Bi ₂ S ₃ dispersion onto a PDMS substrate. Under 980 nm Near‐IR (NIR) illumination, the device demonstrates a photocurrent of 61.2 µA, a responsivity ( R ) of 0.95 A W ⁻¹ , a detectivity ( D ^* ) of 1.4 × 10 ¹² Jones, and an external quantum efficiency (EQE) of 120%. The device also exhibits excellent operational stability, maintaining its initial photocurrent over 650 illumination cycles. It maintains 92% of its photocurrent under bending radii of 12, 10, and 8 mm, and retains ≈90% of its original performance after 20 000 bending cycles at a radius of 8 mm. These results demonstrate that morphology‐controlled Bi ₂ S ₃ nanosheets effectively mitigate brittleness, providing both enhanced mechanical flexibility and reliable photodetection performance.