Recent two decades have seen the rapid development of organic electronics and much attention has been paid to carrier transport behavior. However, other characteristics, such as material compatibility, may be overlooked. We propose a new doping method taking advantage of fused organic solid solution, which is prepared by high-pressure and high temperature processing. In this method, the stable material systems can be selected and high performance organic light-emitting diodes with different colors have been demonstrated.

We report room-temperature, white-color electroluminescence in ZnO nanowires embedded solidly in organic thin films. Excitonic luminescence around 380 nm is observed as a shoulder on a broader, defect-related band covering all of the visible range and centered at 620 nm. The ZnO nanowires are grown in a low-temperature process employing a technique that is suitable for large-area applications. The nanowires are robustly encapsulated in organic films deposited from high-molecular-weight solutions. Electron injection occurs through a transparent SnO2 layer, while hole injection is mediated by a p-doped polymer and an evaporated Au-contact.

From the view point of materials sciences, one of the central issues in organic thin film transistors (TFTs) is the interface between different materials inherent in the device structure. For example, the interface between organic semiconductors and electrodes controls the carrier injection, while the interface between organic semiconductors and gate insulators governs the trap and carrier densities. Here, we show that interface modification with self-assembeld monolayers (SAMs) using polar organosilane molecules offers novel functions in organic TFTs. SAMs on SiO2 gate dielectrics was found to the carrier density at the conduction channel, while the adsorbed SAMs molecules on metal electrodes causes an ambipolar operation in fullerene TFTs. These interface modification techniques, since they are low temperature processes, provide novel opportunities for improving device manufacturing processes.

Thin (12-nm) self-assembled films of the insulating molecule 11-mercaptoundecanoic acid (MUA) were contacted by gold electrodes in a sandwich structure. Current-voltage scans of the resulting devices revealed symmetric negative differential resistance (NDR) with peaks at ±3 V and large peak current densities of up to 104 A/cm2. Devices could be programmed reversibly into nonvolatile high- and low-conductance states by applying 1-ms voltage pulses of 4 V and 10 V, respectively; this conductance could be probed non-destructively with voltages below 2.5 V. A conductance ratio of 103 between the high- and low-conductance states was measured. The NDR is attributed to the dynamic alteration of the device conductivity as the voltage is scanned. Devices fabricated with one gold and one aluminum electrode displayed NDR only for positive bias on the gold electrode, which supports a model in which the observed programming and NDR is due to the movement of gold in the film leading to the formation and destruction of conductive pathways through the insulating layer.

Metal nanoparticles were studied as solution printable precursors to highly conductive elements for electronic device applications. Dispersions of gold and silver nanoparticles stabilized respectively with butanethiol and hexadecylamine in organic solvents were used to prepare electrode features for organic thin film transistors (OTFTs) via stencil printing. The printed features, annealed at a relatively low temperature of 140-160°C, yielded metal electrodes with conductivities resembling those of vacuum-evaporated pure metals. The OTFTs with the source and drain electrodes of this nature exhibited field effect transistor performance identical to those of devices having vacuum-evaporated metal electrodes.

It is difficult to deposit a very thin polymer layer onto a fiber-shaped substrate from solution because the high interfacial energy can lead to dewetting. This difficulty presents itself when attempting to apply a gate dielectric to conductive fiber substrates during the fabrication of fiber transistors for use in applications such as “electrotextiles” and optical switches. We present a dip coating process that applies a gate dielectric to metal-coated optical fibers with high uniformity and reproducibility, resulting in pentacene field-effect transistors (FETs) with excellent transistor characteristics including mobilities up to 0.4 cm2/Vs and on/off ratios up to 7000. In one case, a memory effect was demonstrated. Several gate dielectrics were successfully applied to the optical fibers, suggesting a baseline set of suitable materials for this purpose. A thorough study of the dip coating conditions is presented, including proposed explanations of the effects of different coating procedures and solution physical properties.

We report a novel class of emitting materials for use in the organic light-emitting devices (OLEDs): multifunctional phosphorescent dendrimers that have a phosphorescent core and have charge transporting dendrons. We have synthesized first-generation and second-generation dendrimers consisting of a fac-tris(2-phenylpyridine)iridium [Ir(ppy)3] core and hole transporting phenylcarbazole-based dendrons. Smooth amorphous films of these dendrimers were formed by spin-coating them from solutions. The OLEDs using the dendrimer exhibited bright green or yellowish-green emission from the Ir(ppy)3 core. The external quantum efficiency of the OLED using the mixture film of the first-generation dendrimer and an electron-transporting material was as high as 7.6%.

In this work, blends of dispersed short (∼500 nm) single-walled carbon nanotubes (SWCNTs) with poly(3,4-ethylene dioxythiophene):polystyrene sulfonic acid (PEDOT:PSS) were investigated as hole injection layers in OLEDs consisting of N,N′-di(naphthalene-1-yl)-N,N′-diphenylbenzidine (NPB) as a hole transporting and tris-(8-hydroxyquinoline) aluminum (Alq3) as electron transporting and emitting layer. The devices were characterized by electroluminescence and current-voltage measurements. By comparing the performance of devices fabricated using different surfactants (polyethyleneimine (PEI) and Gum Arabic (GA)) in dispersing SWCNTs and those prepared without surfactants, it was found that the use of appropriate surfactants can improve the OLEDs performance. Improved efficiency was obtained for optimized SWCNTs concentration compared to the devices with pure PEDOT:PSS, although maximum luminance is lower. The PEDOT:PSS:SWCNT nanocomposite layers are characterized and the reasons for the improved OLED performance are discussed.

The main mechanisms responsible for the luminance degradation in OLEDs driven under constant current has not yet been identified. In this paper we propose a new approach to describe the intrinsic mechanisms involved in the OLED aging. We will first show that a stretched exponential decay can be used to fit almost all the luminance vs time curves obtained under different driving conditions. In this way we are able to prove that they can all be described by employing a single free parameter model.

By using as an approach based on local relaxation events, we will demonstrate that a single mechanism is responsible for the dominant aging process. Furthermore, we will demonstrate that the main relaxation event is the annihilation of one emissive center.

We will then use our model to fit all the experimental data measured under different driving condition, and show that by carefully fitting the accelerated luminance lifetime-curves, we can extrapolate the low-luminance lifetime needed for real display applications, with a high degree of accuracy.

This paper reports on a new organic thin-film transistor (OTFT) based on a dual-gate configuration. This dual-gate OTFT is useful in circuit applications from the standpoint of providing control over selected device parameters for enhanced circuit reliability. Moreover, the dual-gate structure can shield parasitic effects in vertically integrated electronics, making it particularly promising for active matrix display and imaging applications. The dual-gate OTFT also lends itself as a highly functional test structure for characterization of interface integrity of the active organic and dielectric layers. In this work, the dual-gate OTFT is fabricated using regioregular poly(3-hexylthiophene) (P3HT) as the organic semiconductor layer. The bottom-gate employs silicon dioxide (SiO2) as the gate dielectric, whereas the top-gate employs a low-temperature amorphous silicon nitride (SiNx) as the passivation dielectric. The voltage on the bottom-gate has a distinct influence on the threshold voltage, subthreshold slope, on-current, and leakage current of the top-gate TFT. Similar dependence of the bottom-gate TFT characteristics on the top-gate voltage is observed. This design provides a means of characterizing the density of states of the bottom P3HT/SiO2 and top P3HT/SiNx interfaces, and conveys insight into the underlying transport mechanisms. The ability to control selected TFT parameters (e.g., threshold voltage) using the dual-gate OTFT structure is attractive for circuit integration applications in active matrix displays and imagers.

We investigated the effect of encapsulation on poly(3-hexylthiophe) (P3HT) bottom-gate field-effect transistors (BG-FETs) with a high on/off current ratio achieved by thermal annealing in N2 atmosphere. The intensity of the oxygen-related absorption peak in the Fourier-transform infrared (FT-IR) spectra of the P3HT films showed a correlation to the on/off current ratio of the FETs. In order to eliminate this oxygen-doping effect, we evaluated three types of encapsulation film: polymer insulator, SiNx, and polymer-SiNx hybrid insulator. We found that the polymer-SiNx hybrid insulator film can suppress both damage caused by the formation of the encapsulation layer and the doping caused by exposure to air. To investigate the effect of encapsulation, we calculated the time dependence of the unintentional dopant density of the P3HT film.