High‐Speed Broadband Self‐Powered Photodetectors Based on Tin Sulfide/Graphitic Carbon Nitride Composites for Environmental Monitoring

Developing photodetectors with rapid response, broad spectral coverage, and self‐powered operation remains a major challenge since they are mutually exclusive. This challenge is tackled by compositing tin sulfide (SnS) and graphitic carbon nitride (g‐C 3 N 4 ) through a controlled incorporation of g‐C 3 N 4 (0.5–15 wt.%), to modulate depletion width, band alignment, and surface defects. The optimized composite (1 wt.% g‐ C 3 N 4 , named SG‐1) exhibits broadband absorption spanning 250–1400 nm, a strong zero‐bias photocurrent (2.24 µA), and rapid rise/decay times of 0.48/0.47 ms, which are among the fastest reported for SnS‐based photodetectors. Scanning Kelvin probe (SKP) analysis reveals a pronounced illumination‐induced work‐function modulation (ΔWF ≈ 0.23 eV), confirming enhanced built‐in field and reduced surface defect density. Correspondingly, SG‐1 achieves a responsivity of 2.8 mA/W and a detectivity of 1.9 × 10 9 Jones that is ∼4× greater than pristine SnS. The combined optical, electrical, and contact potential difference (CPD) establishes that g‐C 3 N 4 ‐driven depletion modulation is instrumental for rapid carrier dynamics. These results validate SnS/g‐C 3 N 4 composites as promising candidates for next‐generation ultrabroadband, low‐power, and high‐speed photodetectors for environmental sensing, optical communication, and IoT‐integrated systems.