Development Of Organic Electronic Devices Research Articles

Phosphonate coupling molecules for the control of surface/interface properties and the synthesis of nanomaterials

Phosphonic acids are increasingly being used for controlling surface and interface properties in hybrid or composite materials, (opto)electronic devices and in the synthesis of nanomaterials. In this perspective article, a concise survey of phosphonate coupling molecules is first presented, including details on their coordination chemistry, their use in the surface modification of inorganic substrates with self-assembled monolayers, and the analytical techniques available to characterize their environment in nanomaterials. Then, some of their recent applications in the development of organic electronic devices, photovoltaic cells, biomaterials, biosensors, supported catalysts and sorbents, corrosion inhibitors, and nanostructured composite materials, are presented. In the last part of the article, a brief overview of recent progress in the use of phosphonate ligands for the preparation of molecular nanomaterials like metal organic frameworks and functionalized polyoxometalates is given.

Light-driven photochromism-induced reversible switching in P3HT–spiropyran hybrid transistors

We demonstrate the use of P3HT–spiropyran blends as an active layer to achieve reversible photoswitching effects in solution-processed organic field-effect transistors (OFETs). Conformational changes of spiropyrans triggered by light with different wavelengths produce two distinct interaction strengths at organic/organic interfaces that can reversibly modulate the channel conductance of OFETs in a noninvasive manner. This concept of organic–organic interfacial modification offers attractive new prospects for the development of organic electronic devices with desired properties.

Interface Engineering of Semiconductor/Dielectric Heterojunctions toward Functional Organic Thin-Film Transistors

Interface modification is an effective and promising route for developing functional organic field-effect transistors (OFETs). In this context, however, researchers have not created a reliable method of functionalizing the interfaces existing in OFETs, although this has been crucial for the technological development of high-performance CMOS circuits. Here, we demonstrate a novel approach that enables us to reversibly photocontrol the carrier density at the interface by using photochromic spiropyran (SP) self-assembled monolayers (SAMs) sandwiched between active semiconductors and gate insulators. Reversible changes in dipole moment of SPs in SAMs triggered by lights with different wavelengths produce two distinct built-in electric fields on the OFET that can modulate the channel conductance and consequently threshold voltage values, thus leading to a low-cost noninvasive memory device. This concept of interface functionalization offers attractive new prospects for the development of organic electronic devices with tailored electronic and other properties.

Predictions of Hole Mobility in Molecular Organic Crystals: Incorporating Thermal Effects

A reliable, cost-efficient method to compute hole mobility, μ, in organic molecular solids would contribute to the development of organic electronic devices by offering a method to rapidly screen a wide variety of materials for desirable transport properties. An existing protocol due to Deng and Goddard(1) [J. Phys. Chem. B 2004, 108, 8614−8621] utilizes Marcus−Hush theory to calculate hole mobility. We have extended the method to account for thermal effects in a way that allows for anisotropy in the interaction potential between molecular monomers. This is accomplished by applying Boltzmann statistics to a discrete representation of the interaction potential to approximate the monomer distribution function. We further show how to improve efficiency by employing a hybrid of DFT and AM1 electronic structure data. DFT is used to obtain information about the molecular monomer and AM1 methodology is used for calculations of dimer-based properties. The hybrid method is very efficient and the calculated values ...

Development of Organic Electronic Devices Using Boronate Esters and Related Heterocycles

Abstract New oligomers containing tricoordinated boron atoms were prepared, and OFET devices based on these compounds were fabricated. These are first examples of OFET devices based on compounds containing tricoordinated boron atoms.

Modification of the sheet resistance of ink jet printed polymer conducting films by changing the plastic substrate

The ink jet printing technology is a relatively novel technique in development of organic electronic devices. The technique consists of working out depositions of organic layers by a piezo-based ink jet printer. In this work polymer conducting films deposited by ink jet printing technique on different plastic substrates has been demonstrated. The poly(3,4-ethylenedioxythiofene)/poly(4-styrenesulfonate) [PEDOT/PSS] and glycerol-modified PEDOT/PSS [G-PEDOT/PSS] were used like conducting inks to be applied on polyester and polyethylene terephthalate (PET) substrates. By means of the change of substrate associated to the deposition number or type of polymer ink used for printing of the conducting films, the sheet resistance can be modified. Such a behavior suggests that plastic substrate fulfills an important role for the changing of sheet resistance of the PEDOT/PSS and G-PEDOT/PSS films made by ink jet printing technique. Films obtained from this technique on different plastic substrates might represent a significant step toward the development and improvement of organic electronic devices.

Ag-Diffusion in the Organic Semiconductor Diindenoperylene

The metallization of organic thin films is a crucial point in the development of organic electronic devices. There is no method established yet to detect trace amounts of metal atoms in the organic thin films after metal deposition. Radiotracer measurements are probably the most sensitive tool to study diffusion and to quantify even very small amounts of material penetrating into the bulk. So far, this has been shown for metals and polymers, but not for thin ordered molecular organic films. Here, the first application of this technique on a well-characterized organic thin film system, diindenoperylene using thermally evaporated Ag containing 110mAg radiotracers is shown. The results show that Ag is mainly adsorbed on the surface, but indicate that already at moderate substrate temperatures small concentrations of Ag can penetrate into the organic thin films and agglomerate at the interface during metallization.

Hole transport in porphyrin thin films

Hole transport in p-type organic semiconductors is a key issue in the development of organic electronic devices. Here the diffusion of holes in porphyrin thin films is investigated. Smooth anatase TiO2 films are coated with an amorphous thin film of zinc-tetra~4-carboxyphenyl! porphyrin ~ZnTCPP! molecules acting as sensitizer. Optical excitation of the porphyrin stimulates the injection of electrons into the conduction band of TiO2. The remaining holes migrate towards the back electrode where they are collected. Current-voltage and capacitance-voltage analysis reveal that the TiO 2 / ZnTCPP system can be regarded as an n- p heterojunction, with a donor density of ND52.0310 16 cm 23 for TiO2 and an acceptor density NA54.0310 17 cm 23 for ZnTCPP films. The acceptor density in porphyrin films increases to 1.3 310 18 cm 23 upon irradiation with 100-mW cm 22 white light. Intensity-modulated photocurrent spectroscopy, in which ac-modulated irradiation is applied, is used to measure the transit times of the photogenerated holes through the films. A reverse voltage bias hardly affects the transit time, whereas a small forward bias yields a decrease of the transit time by two orders of magnitude. Application of background irradiation also reduces the transit time considerably. These observations are explained by the presence of energy fluctuation of the highest-occupied molecular orbital level in the porphyrin films due to a dispersed conformational state of the molecules in the amorphous films. This leads to energetically distributed hole traps. Under short circuit and reverse bias, photogenerated holes reside most of the time in deep traps and their diffusivity is only 7 310 211 cm 2 s 21 . Deep traps are filled by application of a forward bias and by optical irradiation leading to reduction of the transit time and a concomitant increase of the diffusivity up to 2 310 27 cm 2 s 21 .