15 October 2016 Current Affairs: The researchers from the Indian Institute of Science (IISc), Bengaluru have developed a cost-effective, high-performance, self-powered UV photodetector.
The self-powered UV photodetector can use the harvested optical energy for direct self-charging of energy storage devices such as supercapacitor. It can also be used for operating electronic devices in the absence of external power source.
Photodector : Photodector is a device capable of sensing (detecting) or responding to electromagnetic energy, typically light by using the electrical effect of individual photons.
The researchers have developed the photodetector by integrating semiconducting vanadium doped zinc oxide (VZnO) nanoflakes with a conducting polymer. The zinc oxide (ZnO) is the base material for UV detection which can be doped with vanadium to produce photodetectors that are self-powered. The photodetector has superior performance in terms of faster detection of photo signals in the order of milliseconds even when UV light intensity is low.
When doped with vanadium, the microstructure of ZnO changes from nanorods to closely-packed nanoflakes. It causes increase in the surface area to the volume of the material. It also creates surface defects within the band gap of ZnO, which helps in trapping the UV radiation that falls on the nanoflakes. These nanorods are one-dimensional and cause more light reflection from top surface. When UV light enters into pores it undergoes multiple reflections and finally gets absorbed.
Benefits : The nanoflake (VZnO) produces five times more photocurrent, compared with ZnO, which generates only 40 nA photocurrent. Once these nanoflakes are hydrogenated, the current generation capacity further increased to 1,000 nA. When these hydrogenated nanoflakes exposed to UV light, they detect photo signal within milliseconds, which is nearly 100 times faster than conventional UV photodetectors. VZnO nanoflakes structure has 98% light harvesting efficiency which is much higher than 84% seen in ZnO.