Chuan-Yi Yang

Solvent-Annealing-Induced Self-Organization of Poly(3-hexylthiophene), a High-Performance Electrochromic Material

We have systematically studied the self-organization of poly(3-hexylthiophene) (P3HT), an electrochromic material, upon control of the solvent evaporation rate. We characterized these polymer films using atomic force microscopy and X-ray diffraction measurements. Well-ordered P3HT structures were developed after solvent annealing; these highly crystalline structures exhibited enhanced electrochromic contrast and reduced resistance within the film, leading to larger coloration efficiencies and faster switching times. The optical contrast (Delta%T), coloration efficiency, and switching time of the P3HT films increased from 54.2%, 182.6 cm(2) C(-1), and 5.3 s, respectively, prior to solvent annealing to 64.8%, 293.5 cm(2) C(-1), and 3.2 s, respectively, after application of the solvent-annealing conditions.

Dependence of channel thickness on the performance of In2O3 thin film transistors

Bottom gate and top contact thin film transistors were fabricated using In2O3 thin films as active channel layers. Thin films of varying thicknesses in the range 5?20?nm were deposited on an SiO2 gate dielectric by the thermal evaporation process in the presence of high purity oxygen. The results of atomic force microscopy show that all the films exhibit dense grain distribution with a root-mean-square roughness in the range 0.6?8.0?nm. Irrespective of the thickness of the channel layer, the on/off ratio of the device is 104. The channel mobility and resistivity were found to be a strong function of the thickness of the active layer. The Levinson model was used to calculate the trap density and the grain boundary mobility. The low processing temperature shows the possibility of utilizing these devices on flexible substrates such as polymer substrates.

Vertical organic triodes with a high current gain operated in saturation region

The authors report the fabrication of vertical organic triodes operated in the pronounced saturation regions by using two back-to-back pentacene Schottky diodes. The device with an optimized 0.7nm LiF hole injection enhancement layer and a 70nm pentacene emitter can achieve an ultrahigh common-emitter current gain of 48 in the saturation region at a low applied voltage VCE of −4V and a base current density of 0.25mA∕cm2. In addition, the device exhibits a high output current density of 12.1mA∕cm2 and a high on/off current ratio of 103.

Influence of thin metal base thickness on the performance of CuPc vertical organic triodes

In this letter, the characteristics of vertical organic triodes fabricated by using two copper phthalocyanine (CuPc) back-to-back Schottky diodes with different metal base thicknesses are reported. The vertical organic triodes exhibit pronounced saturation regions in the output current-voltage characteristics. The common-emitter current gain reduces with increasing the Al base thickness due to the increase of recombination current at the base end resulted from the reduction of opening voids in the Al metal film. The common-emitter current gain of the device with 4.5nm thick Al base reaches 1.9 at VCE=−6V and JB=2.5mA∕cm2.

Pentacene Thin-Film Transistor with PVP-Capped High-k MgO Dielectric Grown by Reactive Evaporation

Pentacene thin-film transistors operated at low voltages have been realized by employing hybrid dielectrics, poly(4-vinylphenol) (PVP)-capped MgO. The MgO film was deposited by reactive evaporation of magnesium in oxygen. The PVP layer plays a role in modifying the surface morphology of the MgO layer, and the images of atomic force microscopy for the PVP-capped MgO films show a root-mean-square roughness of 1 nm. The hybrid dielectric has a dielectric constant of 7.05 with a dielectric strength. The fabricated pentacene organic thin-film transistors exhibit a mobility of 0.66 cm 2 /V s, a threshold voltage of -2.67 V, and an on/off ratio of 10 3 .

Realization of ambipolar pentacene thin film transistors through dual interfacial engineering

Ambipolar conduction of a pentacene-based field-effect transistor can be attributed to dual interface engineering, which occurs at the dielectric∕semiconductor interface and electrode∕semiconductor interface. While the former was realized by utilizing a hydroxyl-free gate dielectric, the latter was made feasible by the use of appropriate metal source and drain electrodes. The field-effect hole and electron mobilities of 0.026 and 0.0023cm2∕Vs, respectively, were extracted from the transfer characteristics of pentacene organic field-effect transistors utilizing polymethyl methacrylate as the trap-reduction interfacial modified layer and Al as the source and drain (S∕D) electrodes. We demonstrated a complementarylike inverter by using two identical ambipolar transistors and it can be operated both in the first and third quadrants with a high output voltage gain of around 10.

Balancing the ambipolar conduction for pentacene thin film transistors through bifunctional electrodes

We report an effective way to equilibrate hole and electron transport in ambipolar pentacene thin film transistors (TFTs). It was achieved by inserting an ultra thin lithium fluoride (LiF) layer at the electrode/organic interface to form a bifunctional source/drain electrode. It can be observed that the presence of ultrathin LiF layer will facilitate the injection of electrons from source/drain electrodes to organic semiconductor, resulting in a significant enhancement of the n-channel conduction, without sacrificing p-channel conduction for ambipolar pentacene TFTs. These factors make them potential candidates for the organic complementary circuits and inverter circuits of these ambipolar TFTs are also demonstrated.

Ambipolar transport behavior in In2O3/pentacene hybrid heterostructure and their complementary circuits

In this Letter, ambipolar transport properties of a bilayer of In2O3 and a pentacene heterostructure have been realized. While In2O3 thin film transistors exhibited a n-channel behavior, pentacene presumed p-channel characteristics on bare SiO2∕p-Si substrates. However, when a bilayer of In2O3/pentacene was realized on the gate dielectrics, the hybrid structure exhibited both n- and p-channel conductions, depicting an ambipolar transistor behavior. When two identical ambipolar transistors were integrated to establish an inverter structure, a voltage gain of 10 was obtained. The results indicate that these heterostructures can be utilized for the complementary circuits.

Pentacene-Based Planar- and Vertical-Type Organic Thin-Film Transistor

Pentacene-based planar- and vertical-type organic thin-film transistors (OTFTs) are investigated in this paper. High operation voltages are observed for the planar-type OTFTs with top source/drain electrodes, which results from the limitations of channel length and low material mobility. With a reduced channel length, a LiF hole-injection enhancement layer, and a thin metal gate, the vertical-type pentacene OTFTs exhibit a low-voltage operation of less than 5 V and a compatible on/off ratio of larger than 102. The smaller current gain observed from the device under current modulation is attributed to the increase of base recombination current under the common-emitter mode.

Transport mechanisms and the effects of organic layer thickness on the performance of organic Schottky diodes

Experimental results of static and dynamic characteristics for single-layer hole-only devices based on copper phthalcyanine (CuPc) and pentacene are observed in this article. The contribution to injection currents from electrode has been investigated by varying the thickness of the organic film. From the observation of current density versus bias voltage (J-V) characteristics, it is concluded that the space-charge-limited conductivity is the dominant transport mechanism for the organic Schottky diodes. Accordingly, an increase of the organic layer thickness will increase the trapping energy level. However, even with the thin CuPc film down to 50nm, the dynamic cut-off frequency of the device is still limited to 150Hz. Low hole mobility and large active area of the device are responsible for the phenomenon. Dramatic enhancement of cut-off frequency up to 11kHz can be obtained for the pentacene-based Schottky diodes.