Flexible hybrid photodetector based on silver sulfide nanoparticles and multi-walled carbon nanotubes

Herein, we reported a wearable photodetector based on hybrid nanocomposites, such as carbon materials and biocompatible semiconductor nanocrystals (NCs), exhibiting excellent photoresponsivity and superior durability. Currently, semiconductor nanocrystal quantum dots (QDs) containing heavy metals, such as lead or cadmium (in the form of lead sulfide (PbS) and cadmium sulfide (CdS)), are known to display excellent detection properties and are thus widely employed in the fabrication of photodetectors. However, the toxic properties of these heavy metals are well known. Hence, in spite of their enormous potential, the QDs based on these heavy metals are not generally preferred in biological or biomedical applications. These limitations, though, can be overcome by the judicious choice of alternate materials such as silver sulfide (Ag₂S) NCs, which are biocompatible and exhibit multiple excitons in Ag₂S QDs. The other chosen component is a carbon-based material, such as the multi-walled carbon nanotube (MWCNT), which is preferred primarily due to its strong and superior mechanical durability. In this study, a hybrid nanocomposite film was synthesized from Ag₂S NCs and MWCNTs by a simple one-step fabrication process using ultrasonic irradiation. Additionally, this method did not involve any chemical functionalization or post-processing step. The size of Ag₂S NCs in the hybrid film was controlled by the irradiation time and the power of the ultrasonic radiation. Further, appropriate composition ratio of the hybrid composite was optimized to balance the photo-response and mechanical durability of the photodetector. Thus, using this synthetic method, an excellent photoresponsivity property of the device was demonstrated for a near-infrared (NIR) light source with various light wavelengths. Furthermore, no visible change in photoresponsivity was observed for bending motions up to 10⁵ cycles and for a range of angles (0-60°). This novel method provides an eco-friendly alternative to existing functional composites containing toxic heavy metals and is a promising approach for the development of wearable optoelectronic devices.