Enhancement of Photosensitivity in a Low-Operating-Voltage Organic–Inorganic Bilayer Thin-Film Transistor by Using an Asymmetric Source–Drain Electrode

A solution-processed inorganic–organic bilayer semiconductor channel-based red-light-sensitive thin-film transistor (TFT) has been fabricated by using an ion-conducting Li–Al2O3 gate dielectric that limits the operating voltage of this TFT within 2 V. In this device, a high-electron-mobility inorganic metal-oxide semiconductor (SnO2) was used as the primary charge transport layer, whereas the polymer (PIDT-2TPD) was used as the photoactive layer. To improve its red photosensitivity, an asymmetric work function source–drain (S–D) electrode was fabricated, which allows a selective carrier (electron or hole) injection and collection from the channel. Besides, the work function difference of this asymmetric S–D electrode generates a potential difference between electrodes that allows faster charge collection from the channel. As a consequence, the photosensitivity of this asymmetric S–D electrode TFT enhanced by ∼103 times under red illumination with respect to the symmetric S–D electrode TFT and the detectivity of this device increased ∼20 times. In addition, the on/off ratio of asymmetric TFT is 4 times greater than that of the symmetric TFT, whereas the subthreshold swing (SS) of this TFT is reduced from 200 to 144 mV/decade.