Carbon Nanotube Based Flexible UV Sensor on Various Substrates

Flexible and printed electronics are attracting considerable attention since they offer new capabilities that are not possible with conventional rigid substrates. Carbon nanotubes (CNTs) were used here to develop a sensor to detect ultraviolet (UV) radiation. The sensors were made on various flexible substrates including polyimide (PI) films and cellulose paper, and also on glass substrate for comparison. CNT in aqueous solution with varying concentrations was drop-cast onto the active region between the electrodes for resistor type devices. An optimum CNT concentration was identified and the distribution and topographies of the nanotube networks on the substrates were investigated by scanning electron microscopy and atomic force microscopy. All the sensors respond immediately to UV on/off cycles with a change in resistance due to the ability of the nanotubes to adsorb and desorb oxygen on their surface. The sensors with the lowest concentration of CNTs (0.0005 wt.%) exhibit the best response. The sensor made on PI substrate yields the highest response at 71%. The functionality is maintained even after mechanically bending the flexible sensors 1000 times at a curvature radius of 10 mm, which is an advantage for practical applications. Electrodes were printed on the PI substrate and tested outdoor under natural sunlight. The sensor accurately detects UV radiation and could be developed for potential applications such as in wristband or sunglass.