Highly photosensitive thin film transistors based on a composite of poly(3-hexylthiophene) and titania nanoparticles

Organic phototransistors based on a composite of P3HT and $TiO2$ nanoparticles have been fabricated, which show high photosensitivity, fast response, and stable performance under both visible and ultraviolet light illumination, and thus they are promising for applications as low cost photosensors. The transfer characteristic of each device exhibits a parallel shift to a positive gate voltage under light illumination, and the channel current increases up to three orders of magnitude in the subthreshold region. The shift in the threshold voltage of the device has a nonlinear relationship with light intensity, which can be attributed to the accumulation of electrons in the embedded $TiO2$ nanoparticles. It has been found that the device is extremely sensitive to weak light due to an integration effect. The relationship between the threshold voltage change and the intensity of light illumination can be fitted with a power law. An analytical model has been developed to describe the photosensitive behavior of the devices. It is expected that such organic phototransistors can be developed for sensing different wavelengths based on different semiconducting polymers and semiconducting nanoparticles.