The spectral imaging for electroluminescence (EL) characterization in the light emitting diode (LED) based on blends of poly[2,7-(9,9-di-n-octylfluorene)] (PFO) and poly[2,7-(9,9-di-n-octylfluorene)-alt-(1,4-phenylene-((4-sec-butylphenyl)amino)-1,4-phenylene) ] (TFB) was performed using the two dimensional imaging micro-spectroscopy system. We found that EL spectral images varied with increasing applied voltages. The origin for such variation of EL spectral images will be discussed in this report.

Very thin (2.3 – 5.5 nm) self-assembled organic dielectric multilayers have been integrated into organic thin-film transistor (OTFT) structures to achieve sub-1 V operating characteristics. These new dielectrics are fabricated via layer-by-layer solution phase deposition of molecular silicon precursors, resulting in smooth, nanostructurally well-defined, strongly-adherent, thermally stable, virtually pinhole-free, organosiloxane thin films having exceptionally large electrical capacitances (400-700 nFcm-2). These multilayers enable OTFT function at very low source-drain, gate, and threshold voltages, and are compatible with a broad variety of vapor- or solution-deposited p- and n-channel organic semiconductors.

The microstructure of pentacene thin films deposited by thermal evaporation is studied by X-ray diffraction. The transmittance of these films evidences different molecular orbital levels and their related excitonic states. Pentacene photodiodes have been also fabricated on ITO-coated glass substrates with aluminium top electrodes. The current voltage characteristics of such devices are discussed paying special attention to the strongly marked space-charge limited regime. This has been related to trapping in an exponential distribution of localised states in the gap of pentacene. The analysis of the characteristic offers valuable information about such distribution of traps. Finally, the external-quantum-efficiency of these photodiodes shows antibatic features, which evidence the importance of excitonic states in the photovoltaic conversion in pentacene.

Organic thin film transistors for display applications are investigated. Different dielectric materials – inorganic and organic – have been studied with respect to their electrical performance It was found that anodic oxidation is an excellent process to achieve smooth high-k dielectrics with high breakthrough field strength. With the proposed electrolyte electrical properties were further improved. The alignment of pentacene on different insulators as well as transistors characteristics is presented.

Conducting polymer based heterojunctions have been intensively studied because of prominent application in photovoltaic solar cells. It is reported in this work the formation, environmental conditions, of hybrid heterojunctions of cadmium selenide (CdSe) poly 30 ctylthiophene (P3OT) by casting a chemically synthesized P3OT solution onto chemical bath deposited (CBD) or screen-printed (SP) CdSe coatings. By using ITO as contact and gold (Au), silver (Ag) or copper (Cu) as metal contact, the electrical properties CdSe–P3OT heterojunctions were studied at room temperature under environmental conditions. In the case of Au contact, the curves of current density (J) vs. applied potential (V) of both (SP) and CdSe (CBD) coatings indicate that the contacts are quasi ohmic. However, with same metal contact the electrical behavior of CdSe (SP)-doped P3OT heterojunction rectifying and the rectification ratio increases as the weight percentage of P3OT increases in heterojunction structure. Furthermore, a small photovoltage (39 mV) was observed in the hybrid structure for Cu contact. On the other hand, for a CdSe (CBD)-pristine heterojunction Au contact gives an ohmic behavior, but rectifying J-V curves are found with contact.

We report on the microstructure of 2(3)-9(10)-16(17)-23(24)-tetra(2-decyltetradecyloxy)- phthalocyanine/peryleneoleylamine (PcH2/PTCDI) blends. Thin films, to be used as active layers in organic photovoltaic cells, were prepared by spin coating and spin casting of dilute toluene solutions on indium tin oxide (ITO) substrates. The morphology of the thin films has been studied using Tapping Mode (TM) atomic force microscopy (AFM), whereas Scanning Electron Microscopy (SEM) was used to reveal the various top electrode morphologies, inherent to the different film processing conditions.

Properly functionalized indolo[3,2-b]carbazoles represent a new class of stable, high-mobility organic semiconductors for organic thin-film transistor applications. Both 5,11-disubstituted and peripherally substituted indolo[3,2-b]carbazoles with proper substituents self-organized into highly crystalline terrace-layered structures under suitable processing conditions. Organic TFTs using channel semiconductors of this nature exhibited excellent field-effect transistor properties, with mobility to 0.14 cm2 V-1 s-1 and current on/off ratio to 107. By virtue of their relatively low HOMO levels and large band gaps, this class of semiconductors also displayed excellent environmental stability under ambient conditions, an appealing characteristic for organic TFT applications.

In this work, we fabricated near-infrared emitting MOLEDs with two organic layers. The hole transporting layer was N, N′ – di(naphthalene-1-yl) - N,N′- diphenylbenzidine (NPB), while tris(8-hydroxyquinoline) aluminum (Alq) was the emissive and electron transporting layer. The bilayer structure was sandwiched between two silver mirrors. In order to investigate the influence of cavity Q-factor to the emission spectra, devices with different thickness of bottom mirror (anode) were fabricated. The influence of the choice of the bottom mirror (anode) was also investigated, and the devices with copper anode were also fabricated. The devices were characterized by angular dependent electroluminescence, photoluminescence, and transmittance measurements. Possible origins of the observed phenomena are discussed.

The relationship between impurity species included in regioregular poly(3-hexylthiophene) (P3HT) and the field effect transistors (FETs) property was investigated. P3HT synthesized by the Rieke method contained only Zn, Ni and Br (free halogen) as impurities. Several kinds of P3HT with different purities by using purification techniques were prepared, and those P3HT-FETs properties were estimated. As a result, it is revealed that the free halogen is effective dopant to increase the FET mobility, and the removal of the catalyst metal (Zn and Ni) is also effective to decrease off-current.

We have fabricated pentacene field-effect transistors (FETs) on polyimide-sheet films with polyimide gate dielectric layers and parylene encapsulation layer, and investigated the high-temperature performance. It is found that the mobility of encapsulated FETs is enhanced from 0.5 to 0.8 cm2/Vs when the device is heated from room temperature to 160°C under light-shielding nitrogen environment. Furthermore, after the removal of annealing temperatures up to 160°C, the transistor characteristic of mobility and on/off current ratio show no significant changes, demonstration the excellent thermal stability of the present organic FETs.

Organic thin film transistor (OTFT) gas sensors fabricated with an array of different active materials are monitored for shifts in performance characteristics during continuous operation over many days in both inert and ambient environments. We analyze the different patterns of degradation behavior observed in different materials and discuss approaches to decoupling a device's sensor response from its stress response.

Organic Thin Film Transistors are a new class of sensors potentially capable of outperforming chemiresistors. They can be operated at room temperature, offer the advantage of remarkable response repeatability and can function as multi-parameter sensors. In this paper evidence of OTFT response dependence on important parameters such as the chemical nature of the organic semiconductor active layer and the gate-dielectric/organic-semiconductor interface are produced. A sizable response enhancement of an OTFT sensor operated in the enhancement mode is also presented indicating that an OTFT can in principle lead to a lower detection limit than a resistor-type sensor with the same organic semiconductor.

Pentacene thin-film transistors (TFT) were fabricated on aluminum foils using polymethyl methacrylate (PMMA) as gate dielectric. In such structure, the aluminum substrate acts as the gate electrode itself. A bottom gate inverted structure was used to study the influence of the dielectric and the aluminum substrate on the device performance.

Pentacene thin-films were deposited by thermal evaporation in high-vacuum at deposition rates around 3 Ås-1 and three different substrate temperatures (30, 60 and 90°C). The maximum process temperature achieved was 170°C, corresponding to the baking of polymethyl methacrylate. The TFTs exhibit field-effect mobility values of ∼ 10-3 cm2V-1s-1 and threshold voltage values around –15 V. The influence of the dielectric and the substrate temperature on the pentacene structure and device field-effect mobility is discussed.

Polypyrrole exhibits actuation under electrochemical doping and undoping of the polymer matrix. Active strain and x-ray diffraction measurements are performed in order to correlate the microscopic and macroscopic structural changes occurring during actuation. Under galvanostatic reduction, the film shows first a linear contraction with oxidation state due to expulsion of small anions. At 50% of the as-grown doping level, the film reverses direction and begins to expand, possibly due to incorporation of the larger cations. X-ray diffraction, however, does not show a linear contraction or expansion in the crystalline portions of the polymer. The polymer crystallites go through a sudden contraction in one dimension of approximately 14%, and otherwise remain constant. The contraction in the polypyrrole crystals occurs at the 50% doping level, and may be correlated with the reversal of macroscopic actuation.

We demonstrate the tuning of metal work functions by chemically modifying the metal surface through the formation of chemisorbed self-assembled monolayers (SAMs) derived from 1H,1H,2H,2H-perfluorinated alkanethiols and hexadecanethiol. The ordering inherent in the SAMs creates an effective, molecular dipole at the metal/SAM interface, which increased the work function of Ag (φAg∼4.4 eV) to 5.5 eV (Δφ∼1.1 eV) for 1H,1H,2H,2H-perfluorinated alkanethiols. Hexadecanethiol on the other hand shifted φAg to 3.8 eV (Δφ ∼0.6 eV). On Au, the SAM of 1H,1H,2H,2H-perfluorodecanethiol raised φAu (4.9 eV) with 0.6 eV to 5.5 eV, whereas hexadecanethiol decreased φAu by 0.8 eV. These chemically modified electrodes were applied in the fabrication of polymer LEDs and the hole injection into poly[2-methoxy-5-(2′-ethyl-hexyloxy)-1,4-phenylene vinylene (MEH-PPV) was investigated. An Ohmic contact for hole injection between a silver electrode functionalized with the perfluorinated SAMs, and MEH-PPV with a HOMO of 5.3 eV was established. Conversely, a silver electrode modified with a SAM of hexadecanethiol lowered φAg to 3.8 eV blocked the hole injection into PPV, which enables studying the electron transport in composite devices. The electron-only current was measured in a polymer/polymer blend photovoltaic cell based on MDMO-PPV (as donor) and poly[oxa-1,4-phenylene-(1-cyano-1,2-vinylene)-(2-methoxy-5-(3′,7′-dimethyloctyloxy)-phenylene)-1,2-(2-cyanovinylene)-1,4-phenylene] (PCNEPV, acceptor). This method demonstrates a simple and attractive approach to modify and improve metal/organic contacts in organic electronic devices like LEDs, photovoltaic cells, and FETs.

We report on the photovoltaic properties of efficient multilayer devices based on pentacene thin films as a function of light intensity. Light-induced effects are characterized by the refined equivalent circuit model which incorporates an additional shunt resistance and an additional diode whose properties are function of the light intensity. Relative effects of these intensity-dependent parameters as well as the route to further optimization are discussed.

The DC characteristics of a Schottky contact between regioregular poly (3-hexylthiophene) and aluminum are studied in forward and reverse bias regimes. Current-voltage curves of the junction in reverse bias show a resistive path in parallel with the expected Schottky contact. This is the sign of a nonuniform junction between the metal and semiconductor that exhibits ohmic behavior in some regions. Reduction of this parallel resistance and degradation of the Schottky junction are observed over a period of two weeks. Accumulation of undesired ions in the polymer or diffusion of aluminum atoms into the semiconductor are two possible mechanisms which may explain the time dependent behavior of these Schottky junctions.

In this work, optical functions of some widely used OLEDs materials 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP), tris (8-hydroxyquinoline) aluminum (Alq3), (N,N′-di(naphthalene-1-yl)-N,N′- diphenylbenzidine (NPB),poly(3,4,-ethylene dioxythiophene):polystyrene sulfonic acid (PEDOT:PSS) and indium tin oxide (ITO)) were studied using spectroscopic ellipsometry (SE) in the spectral range from 1.55 eV to 4.1 eV (wavelength range of 300 nm to 800 nm). The samples were prepared either by thermal evaporation in high vacuum or spin-coating of thin films onto glass substrates. For determination of the optical functions of ITO, commercial ITO glass was used. Measurements at different incident angles were performed to determine whether the samples can be considered isotropic. The SE data were modeled using an oscillator model (Lorentz for semiconducting and Lorentz-Drude for conducting materials). The absorption spectra were also measured, and the comparison with the data determined by SE is given.

We report the synthesis of photoreactive and light-emitting liquid crystals which can be patterned photolithographically to form polymer networks for use in organic light-emitting diodes. The resolution capability of the photopatterning is investigated using a phase mask of period one micron to spatially modulate the irradiance of ultraviolet light incident to the monomer thin film. A surface relief grating of the same period and depth 85 nm is formed on exposure and washing. An OLED incorporating a novel green light-emitting liquid-crystal has a luminous efficiency of 4.3 lm W-1 at 100 cd m-2 and gives a luminance of 990 cd m-2 at an operating voltage of 10 V.

In this paper, CdO thin films are used for the first time as transparent anodes for organic light-emitting diodes (OLEDs). Highly conductive and transparent CdO thin films have been grown on glass and on single-crystal MgO(100) by low pressure metal-organic chemical vapor deposition (MOCVD) at 400°C, and were implemented in small-molecule OLED fabrication. Device response and applications potential have been investigated and compared with those of commercial ITO-based control devices. It is found that as-deposited CdO thin films are capable of injecting holes into such devices, rendering them promising anode materials for OLEDs. A maximum luminance of 32,000 cd/m2 and an external forward quantum efficiency of 1.4 %, with a turn-on voltage of 3.2 V are achieved on MgO(100)/CdO-based devices.