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

A sulfur-assisted one-pot strategy is developed to synthesize ultrathin bismuth sulfide (Bi₂S₃) 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 Bi₂S₃ 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 Bi₂S₃ 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 × 10¹² 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 Bi₂S₃ nanosheets effectively mitigate brittleness, providing both enhanced mechanical flexibility and reliable photodetection performance.