Design and fabrication of a zero-bias visible light photodetector based on a coumarin-derived Schiff base thin film

A self-powered visible-light photodetector was fabricated using a coumarin-derived Schiff base, 4-FMCSB, as the active layer. The compound was synthesized via a two-step process and characterized using FT-IR, NMR, MALDI-TOF-MS, and UV-vis spectroscopy. The optical band gap of 4-FMCSB was determined to be 2.33 eV, with DFT calculations confirming a HOMO-LUMO gap of 2.79 eV. Thin films of 4-FMCSB were deposited on ITO substrates via spin coating, and aluminium contacts were thermally evaporated to form Al/4-FMCSB/ITO photodetectors. The device exhibited a strong rectification ratio, rapid photo response (rise time: 510 ms; fall time: 210 ms), and efficient operation under zero bias. Key performance metrics included a responsivity of 12.6 mA W^-1, detectivity of 9.31 × 10¹⁰ jones, and a linear dynamic range of 35.94 dB. These findings underscore the potential of coumarin-based Schiff bases in advancing the design of next-generation, energy-efficient optoelectronic devices.