Stimuli-Responsive Reversible Band-Gap Engineering: Application of Oligo(p-phenylenevinylene) Derivatives for Visible-Light-Driven Photodetector Applications

Oligo-polyvinylene (OPV) compounds, with their conjugated structures, are widely used in optoelectronics due to the efficient charge generation and transport upon light absorption. Their high mobility, low response time, and strong sensitivity with a large signal-to-noise ratio make them ideal for photodetectors. By tuning their molecular structure and modifying the charge moieties and work function, their absorption spectra can be engineered. Protonation of OPV compounds enhances charge transfer and causes a red-shift in absorption from the UV to the visible region, indicating a reduced band gap and improved visible light absorption. The photodetection experiment was conducted under UV and visible illumination for both protonated and unprotonated samples. It was observed that the protonated samples exhibited higher responsivity compared to the unprotonated samples under both UV and visible illumination because of the higher charge transfer capability. Moreover, the deviation in responsivity of protonated samples is very high under visible illumination (2.57 × 10 –3 to 9.34 × 10 –3 A/W) compared to UV illumination (4.47 × 10 –4 to 5.57 × 10 –4 A/W), which is due to a shift in the absorption spectra of the protonated sample from the UV to the visible region and decrease in energy band gap. Thus, modulating the molecular structure of OPV compounds and converting unprotonated species to protonated species find extended application in various fields of optoelectronic applications.