Low cost UV sensor using ZnO nanorods on ITO electrodes

Abstract

Ultraviolet (UV) sensors have gained a lot of importance in the field of environmental sciences, due to their pollution monitoring applications. The current limitations of the UV sensors are their higher temperature operability resulting in high power consumption, degradation and low efficiency. Hence an attempt was made to fabricate room temperature (RT) operable, UV index sensors, using ZnO nanorods on Indium Tin Oxide (ITO) electrodes. The nano rods were grown using hydrothermal method with an optimized concentration and growth duration of 5 mM and 3 h respectively. The vertical rods with a hexagonal face, showed an aspect ratio of six, with weak quantum confinement and a strain of the order of ∼0.002. Nanorods were polycrystalline with an average crystallite size of 50 nm. The broad emission spectra were mostly seen in blue region, with transitions due to singly and doubly ionized zinc interstitials, whose concentration increased with increase in growth duration. The UV response in direct sunlight gave a sensitivity of 118, with rise time and fall time of 35 s and 65 s respectively. The experiments not only yielded reproducible results but the UV index profile for the sensor in response to sunlight, over a full day was in accordance with the profile of the standard WHO sensor. This is of great significance especially from the point of view of ozone depletion, health concerns like skin cancer and environment pollution.