Appl. Phys. Lett. 100, 211104 (2012)

Credit: © 2012 AIP

Paper and pencil — long-valued tools for writers and artists — may also have unexpectedly useful applications in optoelectronics. Kamran ul Hasan and co-workers from Linköping University in Sweden have developed a paper-based ultraviolet-light sensor by printing an ink containing ZnO nanocrystals onto paper covered with pencil-drawn graphite electrodes. Illuminating the paper with 365 nm ultraviolet light generates electron–hole pairs, causing a rapid rise in photocurrent followed by a slow fall once the light is switched off. The researchers say that their sensor, despite being highly economical and easy to fabricate, demonstrates characteristics comparable to those made through more expensive and complex techniques. Experiments suggest that the use of a 4B pencil creates the best graphite electrodes, with a line resistance of around 3 MΩ.