Optical responses and optically program-electrically erase memory in organic transistors

The energy levels of organic semiconductor materials; poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl C₆₁-butyric acid methyl ester (PCBM), were investigated using photo-electron spectroscopy in air (PESA) and UV-Vis spectrophotometer. Solution-processed organic thin-film transistors (OTFTs) based on P3HT/PCBM blend thin film in a top source-drain contact structure was fabricated, and the optical response and memory effects of the devices were also investigated. A unipolar property with p-channel characteristics were obtained in dark condition, and upon an optical response, the drain current was increased. Moreover, the drain current was decreased gradually with delay time after turning off the light, while negative gate bias was required to revert back to initial dark condition. The memory effects of the P3HT/PCBM-OTFTs were attributed to the photocurrent induction and electron trapping-detrapping capability of PCBM nanoparticles. The optical-electro memory effect based on the OTFTs can be programmed optically and erased electrically.