Printed electronics (PE) represents any electronic devices, components or circuits that can be processed using modern-day printing techniques. Field-effect transistors (FETs) and logics are being printed with intended applications requiring simple circuitry on large, flexible (e.g., polymer) substrates for low-cost and disposable electronics. Although organic materials have commonly been chosen for their easy printability and low temperature processability, high quality inorganic oxide-semiconductors are also being considered recently. The intrinsic mobility of the inorganic semiconductors are always by far superior than the organic ones; however, the commonly expressed reservations against the inorganic-based printed electronics are due to major issues, such as high processing temperatures and their incompatibility with solution-processing. Here we show a possibility to circumvent these difficulties and demonstrate a room-temperature processed and inkjet printed inorganic-oxide FET where the transistor channel is composed of an interconnected nanoparticle network and a solid polymer electrolyte serves as the dielectric. Even an extremely conservative estimation of the field-effect mobility of such a device yields a value of 0.8 cm(2)/(V s), which is still exceptionally large for a room temperature processed and printed transistor from inorganic materials.

Light-emitting electrochemical cells (LECs) are fabricated by gravure printing. The compromise between device performance and printing quality is correlated to the ink formulation and the printing process. It is shown that the rheological properties of the ink formulations of LECs can be tailored without changing the chemical composition of the material blend.

Printing organic semiconductor inks by means of roll-to-roll compatible techniques will allow a continuous, high-volume fabrication of large-area fl exible optoelectronic devices. The gravure printing technique is set to become a widespread process for the high throughput fabrication of functional layers. The gravure printing process of a poly-phenylvinylene derivative light-emitting polymer dissolved in a two solvent mixture on poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) is studied. The surface tensions, contact angles, viscosities, and drying times of the formulations are investigated as a function of the solvent volume fraction and polymer concentration. The properties of the ink grant a homogeneous printed layer, suitable for device fabrication, when the calculated fi lm leveling time is shorter than a critical time, at which the fi lm has been frozen due to loss of solvent via evaporation. The knowledge obtained from the printing process is applied to fabricate organic light-emitting diodes (OLEDs) on fl exible substrates, yielding a luminance of ≈ 5000 cd m − 2 .

Photoinduced changes in the mechanical and dielectric properties of azobenzene polymer films were measured utilizing the method of electromechanical spectroscopy. The measurements revealed a strong correlation between the time-dependent behavior of the plate compliance and the dielectric constant under irradiation. Actinic light causes a light softening of the film that also manifests itself in the increase of the dielectric constant, whereas ultraviolet irradiation results in an initial plasticization of the film followed by its hardening. The latter is accompanied by decrease of the dielectric constant. A semiquantitative model based on the kinetics of the photoisomerization process in azobenzene polymers is proposed. We assume that both visible and ultraviolet irradiation increase the free volume in the layer due to photoisomerization. Additionally, ultraviolet light increases the modulus of the polymer matrix due to the presence of a high density of azobenzene moieties in the cis state. These assumptions allowed us to reproduce the time-dependent behavior of the bulk compliance as well as the dielectric constant at different irradiation intensities, for both visible and ultraviolet light, with only two adjustable parameters.

We study two types of water/alcohol-soluble aliphatic amines, polyethylenimine (PEI) and polyethylenimine-ethoxylated (PEIE), for their suitability as electron injection layers in solution-processed blue fluorescent organic light-emitting diodes (OLEDs). X-ray photoelectron spectroscopy is used to determine the nominal thickness of the polymer layers while ultraviolet photoelectron spectroscopy is carried out to determine the induced work-function change of the silver cathode. The determined work-function shifts are as high as 1.5 eV for PEI and 1.3 eV for PEIE. Furthermore, atomic force microscopy images reveal that homogeneous PEI and PEIE layers are present at nominal thicknesses of about 11 nm. Finally, we solution prepare blue emitting polymer-based OLEDs using PEI/PEIE in combination with Ag as cathode layers. Luminous efficiency reaches 3 and 2.2 cd A(-1), whereas maximum luminance values are as high as 8000 and 3000 cd m(-2) for PEI and PEIE injection layers, respectively. The prepared devices show a comparable performance to Ca/Ag OLEDs and an improved shelf lifetime.

Nanoparticulate zinc oxide is regarded as one of the most promising inorganic materials for printable field-effect transistors (FETs), which work in the n-channel enhancement mode, due to the compatibility with solution, low-temperature, and high throughput processes. Since nanoparticulate films are composed of the nanoparticles and their agglomerates, the roughness of the interface to the insulating layer, where the channel of the FETs is formed, is a critical issue. Thus, the influence of the interface roughness on the field-effect mobility of the FETs is investigated in conjunction with film roughness and capacitance analyses. The field-effect mobility increases almost by a factor of 50, from 2.0×10−4 to 8.4×10−3 cm2 V−1 s−1, even if the reduction in the average roughness of the films is as small as 1.7 nm.

Field-effect mobilities are the most important figures of merit to evaluate the feasibility of semiconductors for thin-film transistors ͑TFTs͒. They are, however, sometimes extracted from TFTs with the active semiconductor area undefined and in small channel ratios without the effect of the fringing electric field at the ends of source/drain electrodes taken into account. In this letter, it is demonstrated that the field-effect mobilities extracted from undefined nanoparticulate zinc oxide ͑ZnO͒ TFTs at the channel ratio of 2.5 are overestimated by 418%, and the choice of large channel ratios gives the real value of field-effect mobilities.Thin-film transistors ͑TFTs͒ fabricated in lowtemperature and high throughput processes are in great demand for low-cost and large-area production. 1 Organic semiconductors, including small molecules 2 and conjugated polymers, 3,4 have intensively been studied and developed for TFTs, taking the advantage of compatibility with lightweight and flexible substrates. As an alternative route, inorganic semiconductors, including crystalline oxides 5-7 and amorphous oxides, 8,9 have been attracting significant interest in the past decade. 10 These inorganic TFTs generally work in the n-channel mode and benefit from transparency to visible lights, processibility with solutions, and compatibility with lightweight and flexible substrates as well. In order to evaluate the feasibility of any semiconducting material for TFTs, the most important figure of merit is the field-effect mobility . It is frequently extracted from the transfer characteristics of TFTs in the saturation regime, according to the equationwhere C i is the gate capacitance per unit area, W and L are the channel width and length, respectively, and I ds , V gs , and V th are the drain current, the gate voltage, and the threshold voltage, respectively. The channel ratio is commonly defined by W / L. In the case of polycrystalline zinc oxide ͑ZnO͒ TFTs, 11-14 early investigations have shown of 0.1-1.2 cm 2 V −1 s −1 for a channel ratio of 6-40. However, it has been reported that the fieldeffect mobility strongly depends on the channel ratio, ranging from 1.9 to 27 cm 2 V −1 s −1 for the channel ratio from 64 to 1.4. 15-17 Figure 1͑a͒ shows a top-view image of a typical TFT in the bottom gate configuration with the active semiconductor area undefined. It is expected that, particularly in the case of small channel ratios, the effective channel width W eff is not equivalent to the geometrical channel width W 0 but is extended somewhat because of the fringing electric field at the ends of the electrodes, which can lead to the overestimation of the field-effect mobility. Actually, the mobilities reported on the undefined TFTs 12,14-17 seem much higher than those reported on the defined TFTs, 11,13 if they are compared at the same channel ratio. In this letter, therefore, nanoparticulate ZnO TFTs in the bottom gate configuration are modeled with the channel width extensions ⌬W 1,2 included in the effective channel width W eff , as s...

Highly transparent and conducting Al-doped ZnO (AZO) films are prepared via sol-gel method with a broad range of nominal Al-doping. The film porosity and morphology is determined by the rate of temperature ramping during the drying of the gel phase. The minimum resistivity is observed to occur around 1.5–2 at. % Al-doped films, irrespective of the morphology and microstructure. It is found by local chemical analysis that Al tends to segregate at the grain boundaries and above a critical concentration, the segregated Al starts to dominate the electronic transport in nanocrystalline AZO. The optical measurements corroborate these findings showing a systematic increase in carrier density only up to 1.5–2 at. % Al-doping. It is concluded that the presence of the resistivity minimum is not merely determined by a solubility limit but is a result of the interplay between the changing carrier concentration and carrier scattering at the segregated Al.