Photosensitivity study of nano-structured conducting polypyrrole (PPy) thin films

Photosensitive nano-structured materials have a great importance in a variety of industrial and scientific applications, including image sensing, environmental monitoring, remote control, chemical/biological sensing and photodetectors [1]. In this research, the photosensitivity to Near Infrared (NIR) radiation (0.75–1.4 µm) of the nano-structured conducting polypyrrole (PPy) thin films was studied. The soluble conducting PPy was chemically synthesized and the electrospray coating method was applied for deposition of semiconducting PPy on the surface of interdigital electrodes (IDEs). The prepared nano-structered thin film showed good conductivity. This film was then connected as one resistance in one arm of a designed Wheatstone bridge and then its photoresistivity properties were investigated. The changes in the electrical resistance and the amount of passing current of designed circuit were measured when the photoresistive film illuminated in NIR region. Observations showed that the initial resistance (R0) of the nano-structured thin film decreased by 10% (R1) of its value when the film was exposed to the NIR radiation source . When the NIR source was then turned off, R1 gradually returned to the original value Ro with good repeatability. In addition, a current of about 0.07mA is passed through a Wheatstone bridge circuit when the film illuminated in different wave numbers (4000-400). As a result, these nano-structured semiconducting thin films are good choice as light sensing elements in organic optoelectric devices.