Organic thin film transistors based on poly(3,3‴-didodecylquarter-thiophene) were characterized under illumination with a fixed wavelength but various intensities from dark to 1100 μW cm−2. Typically the illumination process should increase the drain current through the increase in the number of charge carriers in the channel in the form of polarons, as a result of generation and dissociation of excitons or electron-hole pairs. However, the rate of the current increase was found to decrease as the light intensity was increased, and eventually the level of drain current reached a maximum before declining. We suggest that the physics behind this oversaturation behavior is related to the increasing number of electron-hole recombination events associated with the increase in polaron density in the channel. When the polaron density goes above a threshold value at high light intensity, the number of polarons cannot increase further as they are already closely packed and the recombination overtakes generation, resulting in a decrease in the drain current from its peak value. We show that quantitative analysis agreed well with our model, and in our device the polaron diameter and mean free path are 19 and 2 nm, respectively.

The apparent shift of threshold voltage of organic thin-film transistors under light illumination has been explained as a result of the superposition of a photo-generated current on the dark current overall biases. Our model has been confirmed by demonstrating that the apparent threshold voltages calculated under different illumination intensities matched perfectly with the experimental values, for two devices with different channel widths. Our model indicates that (1) there is a photo-current associated with the photo-excitation process in organic thin-film transistors and (2) the apparent threshold voltage under illumination is not the intrinsic threshold voltage of a device as measured in the dark; instead, it is monotonically shifted from the intrinsic value due to the increase in photo-current under normal laboratory conditions.

A novel triode device controlled by a carrier type (namely, “carristor”) with ultrahigh on/off and rectification ratios is introduced.

Next-generation flexible and transparent electronics demand newer materials with superior characteristics. Tin dichalcogenides, Sn(S,Se)2, are layered crystal materials that show promise for implementation in flexible electronics and optoelectronics. They have band gap energies that are dependent on their atomic layer number and selenium content. A variety of studies has focused in particular on tin disulfide (SnS2) channel transistors with conventional silicon substrates. However, the effort of interchanging the gate dielectric by utilizing high-quality hexagonal boron nitride (hBN) still remains. In this work, the hBN coupled SnS2 thin film transistors are demonstrated with bottom-gated device configuration. The electrical transport characteristics of the SnS2 channel transistor present a high current on/off ratio, reaching as high as 105 and a ten-fold enhancement in subthreshold swing compared to a high-κ dielectric covered device. We also demonstrate the spectral photoresponsivity from ultraviolet to infrared in a multi-layered SnS2 phototransistor. The device architecture is suitable to promote diverse studied on flexible and transparent thin film transistors for further applications.

Molybdenum disulfide (MoS) film fabricated by a liquid exfoliation method has significant potential for various applications, because of its advantages of mass production and low-temperature processes. In this study, residue-free MoS thin films were formed during the liquid exfoliation process and their electrical properties were characterized with an interdigitated electrode. Then, the MoS film thickness could be controlled by centrifuge condition in the range of 20 ∼ 40 nm, and its carrier concentration and mobility were measured at about 7.36 × 10 cm and 4.67 cm V s, respectively. Detailed analysis on the films was done by atomic force microscopy, Raman spectroscopy, and high-resolution transmission electron microscopy measurements for verifying the film quality. For application of the photovoltaic device, a Au/MoS/silicon/In junction structure was fabricated, which then showed power conversion efficiency of 1.01% under illumination of 100 mW cm.