Stretchable photodetector utilizing the change in capacitance formed in a composite film containing semiconductor particles

Conventional photodetectors (PDs) are based on measuring photocurrent, which is formed by the separation of electron-hole pairs generated in semiconductors upon light irradiation, through electrodes in direct contact with the semiconductors. Such devices are usually fabricated through complicated and precise processes such as thin film formation by vacuum deposition and fine patterning by photolithography and etching. In addition, PDs have a drawback that the contact quality between the electrode and the semiconductor is easily affected by external stress applied to the device. These issues make it difficult to implement a mechanically flexible device driven by conventional sensing mechanisms. Here we report a simple structured PD based on a semiconductor particle-polymer composite layer surrounded by two facing transparent electrodes, inspired by the fact that the dielectric properties of certain semiconductors change upon light irradiation with a photonic energy greater than or equal to their bandgap. In order to realize this, we synthesized a transparent and stretchable polymer, polyurethane-urea (PUU), which is compatible with Ag nanowires (AgNWs) and polydimethylsiloxane (PDMS) used for implementing stretchable electrodes, and dispersed ZnS:Cu particles into the PUU to form a sensory layer. The fabricated composite surrounded by two facing AgNW-based transparent electrodes was transparent and stretchable, and the capacitance formed at the composite sensitively changed upon irradiation of light with a wavelength of 420 nm and a power of 1.2 mW/cm2 even when the device was stretched or cut in half.