We report the synthesis, characterization, and implementation of various naphtho[2,3- b:6,7-b’]dithiophene (NDT)-based donor molecules for organic photovoltaics (OPVs) When NDT(TDPP)2 (TDPP = thiophene-capped diketopyrrolopyrrole) contains all branched 2- ethylhexyl chains and is combined with the electron acceptor PC61BM, a power conversion efficiency (PCE) of 4.06±0.6% is achieved. This respectable PCE is attributed to the broad, high oscillator strength visible absorption, the ordered molecular packing, and a high hole mobility of 0.04 cm2·V-1·s-1. We find utilizing linear C-12 side chains on either the TDPP or NDT framework dramatically increases the d-spacing, which directly correlates with inferior OPV device performance. This leads to the conclusion that the selection of an appropriate side chain plays a key role in determining OPV device performance of a small molecule donor.

Materials scientists involved in synthesis are exceptionally skilled at designing and constructing individual molecules with the goal of introducing rationally tailored chemical and physical properties. However, the task of assembling such special molecules into organized, supramolecular structures with precise, nanometer-level organizational control to execute specific functions presents a daunting challenge. Soft and hard matter suitable for unconventional types of electronic circuitry represents a case in point and, in principal, offer capabilities not readily achievable with conventional silicon electronics. In this context, “unconventional” means circuitry that can span large areas, can be mechanically flexible and/or optically transparent, can be created by large-scale, high-throughput fabrication techniques, and has atomic-level tunability of properties. In the process of preparing, characterizing, and fabricating prototype devices with such materials, we learn many new things about the electronic and electrical properties of the materials and the interfaces between them. This account briefly overviews recent progress in three interconnected areas: (1) organic semiconductors for complementary π-electron circuits, (2) soft matter high-κ gate dielectrics for organic and inorganic electronics, and (3) metal-oxide semiconductors as components in such devices. Space limitations allow only touching upon selected highlights in this burgeoning field.

Pentacene is one of the most studied semiconductor for organic thin-film transistors (OTFTs), and enhanced understanding of pentacene-based TFTs has significantly advanced the organic electronics. We report here the crucial effect of the polymer gate dielectric glass transition temperature (Tg) on pentacene film growth mode, microstructure, and the resulting TFT performance. Nanoscopically-confined thin polymer films are known to exhibit reduced glass-transition temperatures versus the corresponding bulk values, and we demonstrate here that pentacene films grown on polymer gate dielectrics at temperatures well below their bulk Tg exhibit morphological/microstructural transitions and OTFT performance discontinuities at well-defined growth temperatures [defined as the surface Tg, or Tg(s)] characteristic of the underlying polymer structure and independent of the film thickness. The results argue that realistic OTFT response must take into account this fundamental polymer property, and that TFT measurements represent a new probe of polymer surface thermal properties.

A series of highly near-infrared (NIR) transparent In2O3 thin films has been grown by ion-assisted deposition (IAD) at room temperature, and their optical and electrical properties characterized. The NIR transparency and the plasma edge can be engineered through control of the film deposition conditions. The as-deposited In2O3 thin films were employed as transparent electrodes for direct electro-optic (EO) characterization measurements via the Teng-Man technique. Using LiNbO3 as the standard, the relationship between the degree of electrode NIR transparency and Teng-Man EO measurement accuracy was evaluated. It is found that In2O3 electrodes can be tailored to be highly NIR transparent, thus providing more accurate Teng-Man EO coefficient quantification than ITO (tin-doped indium oxide). In addition, the EO coefficients of stilbazolium-based self-assembled superlattice (SAS) thin films were directly determined for the first time by the Teng-Man technique using an optimized In2O3 electrode. EO coefficients r33 of 42.2, 13.1, and 6.4 pm/V are obtained at 633, 1064, and 1310 nm, respectively.

Organic semiconductors exhibiting p-, n-type, or ambipolar majority charge transport are grown on six different bilayer dielectric structures consisting of various spin-coated polymers / HMDS on 300 nm SiO2/p+-Si, and are characterized by AFM, SEM, and WAXRD, followed by field-effect transistor (FET) electrical characterization. It is observed that in case of air-sensitive n-type semiconductors, dielectric surface modifications induce large variations in the corresponding OTFT performance parameters although the film morphologies and microstructures remain similar. In marked contrast, the device performance of air-stable n-type and p-type semiconductors is not significantly affected by the same dielectric surface modifications. This study provides key information on the chemical origin of the charge trapping sites at the FET dielectric-semiconductor interface. In parallel, bottom-contact FETs of n-type oligothiophenes were investigated by a combination of microscopy/electrical measurements and new insights for the poor electron injection efficiency from the Au contacts are presented

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.

We present our latest results on the design and fabrication of very high capacitance dielectric materials for organic field-effect transistors. We will show that utilization of appropriate self-assembling siloxane building blocks and polymer matrices allows solution-processed, pinhole-free organic dielectrics. Electrical (MIS, TFT) data demonstrate that these insulators can be efficiently integrated into large TFT structures. These devices function for both p- and n-channel semiconductors, the molecular components of which exhibit greatly different core structures and substituent functionalities. Substantial TFT response is achieved at very low operational biases (<1V), without serious leakage currents (<10-8 A/cm at 1V).

A series of unconventional twisted intramolecular charge-transfer (TICT) chromophores was designed and synthesized. These chromophores exhibit ultra-large first hyperpolarizabilities. The structural characteristic that promotes this unusual nonlinear optical response is a sterochemically enforced reduction of the D- π-A conjugation that enforces zwitterionic behavior in the ground state and provides a low-energy, large-oscillator strength intramolecular excitation feature. The consequence is that molecules with relatively small numbers of π-electrons exhibit responses far larger than those of traditional planar π-conjugated chromophores. At 1907 nm, non-resonant νβ values as high as -466,000 × 10-48 esu are observed.

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.

Organic semiconductors exhibiting complementary n-type carrier mobility are the key components for the development of the field of “plastic electronics”. We present here a novel series of oligothiophenes designed to improve performance and stability under electron- transporting conditions. Furthermore, the key structural features of these compounds allows additional modifications of the n-type conducting core to achieve material solubility and processability. Thin film transistor (TFT) devices were fabricated employing both vacuum- and solution-deposited semiconducting layers. Field-effect transistor measurements indicate that all the members of this new series are n-type semiconductors with mobilities and Ion:Ioff ratios approaching 1 cm2/(Vs) and 107, respectively. This family represents a key milestone in the design, understanding, and development of the next generation of highly efficient n-type OTFT components.

Organic semiconductors exhibiting complementary-type carrier mobility are the key components for the development of the field of “plastic electronics”. We present here a novel series of αω- and isomerically pure β,β'-diperfluorohexyl-substituted thiophene and study the impact of fluoroalkyl substitution and conjugation length vìs-à-vìs the corresponding fluorinefree analogues. Trends between the fluorinated and fluorine-free families in molecular packing, HOMO-LUMO gap, and π-π interactions are found to be strikingly similar. TFT measurements indicate that all members of the fluorinated series are n-type semiconductors

Organic semiconductors exhibiting complementary-type carrier mobility are the key components for the development of the field of “gplastic electronics” We present here a novel series of α,ω- and isomerically pure ββ'-diperfluorohexyl-substituted thiophene and study the impact of fluoroalkyl substitution and conjugation length vis-a-vis the corresponding fluorinefree analogues. Trends between the fluorinated and fluorine-free families in molecular packing, HOMO-LUMO gap, and π-π interactions are found to be strikingly similar. TFT measurements indicate that all members of the fluorinated series are n-type semiconductors

Gallium–indium–oxide films (GaxIn2⊟xO3), where x = 0.0–1.1, were grown by low-pressure metalorganic chemical vapor deposition using the volatile metalorganic precursors In(dpm)3 and Ga(dpm)3 (dpm = 2,2,6,6-tetramethyl-3,5-heptanedionato). The films were smooth (root mean square roughness = 50–65 Å) with a homogeneously Ga-substituted, cubic In2O3 microstructure, randomly oriented on quartz or heteroepitaxial on (100) yttria-stabilized zirconia single-crystal substrates. The highest conductivity of the as-grown films was found at x = 0.12, with σ = 700 S/cm [n-type; carrier density = 8.1 × 1019 cm⊟3; mobility = 55.2 cm2/(V s); dσ/dT<0]. The optical transmission window of such films is considerably broader than that of Sn-doped In2O3, and the absolute transparency rival or exceeds that of the most transparent conductive oxides known. Reductive annealing, carried out at 400–425 C° in a flowing gas mixture of H2 (4%) and N2, resulted in increased conductivity (σ 1400 S/cm; n-type), carrier density (1.4 × 1020 cm⊟3), and mobility as high as 64.6 cm2/(V s), with little loss in optical transparency. No significant difference in carrier mobility or conductivity is observed between randomly oriented and heteroepitaxial films, arguing in combination with other data that carrier scattering effects at high-angle grain/domain boundaries play a minor role in the conductivity mechanism.

The design, synthesis, and properties of two mixed perfluorophenyl-thiophene oligomers 5,5″′-diperfluorophenyl-2,2′:5′,2″:5″,2″′:5″′,2″″:5″″,2″″′-quaterthiophene (2) and 5,5′-bis{1-[4-(thien-2-yl)-2,3,5,6-tetrafluorophenyl)] }-2,2′-dithiophene (3) are presented. Molecular characterization included the following techniques: multinuclear NMR, DSC and TGA, optical UV-Vis and photoluminescence spectroscopy, and cyclic voltammetry. Thin films can be easily grown by vacuum evaporation and have been characterized by optical UV-Vis and photoluminescence, XRD, and field-effect transistor measurements. Electron and hole mobilities of 0.06–0.08 cm2/(V s) and 0.001–0.003 cm2/(V s) were found for 2 and 3, respectively.

A new series of low-melting, highly volatile, thermally and air-stable cadmium MOCVD precursors have been synthesized and characterized. Cd(hfa)2(N, N-DE-N', N'-DMEDA) has been successfully utilized in the growth of highly conductive and transparent CdO thin films. Hall measurements conducted on films deposited simultaneously on MgO (100) single crystal and Corning 1737F glass substrates reveal that the films on MgO have significantly enhanced carrier mobilities. Owing to similar grain sizes and carrier concentrations we attribute this effect to improved texture and associated improvements crystalline order. Conductivities as high as 8,590 S/cm are obtained which is to our knowledge the highest value reported to date for CdO films without aliovalent dopants.

Phase-selective growth of TlBa2Ca2Cu3O9−x films is greatly enhanced by annealing chemical vapor deposition derived BaCaCuO(F) precursor films in the presence of TlF. Nucleation of superconducting phases (≥840 °C under O2) progresses in the order 2212 → 2223 → 1212 → 1223. Annealing at 855 °C results in well-defined platelet grains, a significant number of which are a-axis oriented. Residual fluoride is not detectable at any stage of the annealing process. Thin films synthesized by TlF annealing differ markedly from films processed in the presence of Tl2O3 with Tc = 103 K and Jc > 105 A/cm2 (5 K, 4.5 T).

High-quality epitaxial or highly textured NiO thin films can be grown at temperatures of 400–750°C by low-pressure metalorganic chemical vapor deposition (MOCVD) on MgO, SrTiO3, C-cut sapphire, as well as on single crystal and highly textured Ni (200) metal substrates using Ni(dpm)2 (dpm – dipivaloylmethanate) as the volatile precursor and O2 or H2O as the oxidizer/protonolyzer. X-ray diffraction (XRD), scanning electron microscopy/energy dispersive detection (SEM/EDX), and atomic force microscopy (AFM) confirm that the O2-derived NiO films are smooth and that the quality of the epitaxy can be improved by decreasing the growth temperature and/or the precursor flow rate. However, low growth temperatures (400–500 °C) lead to rougher surfaces and carbon contamination. The H2O-derived NiO films, which can be obtained only at relatively high temperatures (650–750 °C), exhibit slightly broader ω scan full width half-maximum (FWHM) values and rougher surfaces but no carbon contamination. Using H2O as the oxidizer/protonolyzer, smooth and highly textured NiO (111) films can be grown on easily oxidized single crystal and highly textured Ni (200) metal substrates, which is impossible when O2 is the oxidizer. The textural quality of these films depends on both the quality of the metal substrates and the gaseous precursor flow rate.

This communication reports rapid, efficient syntheses of the zirconium-organic metal-organic chemical vapor deposition (MOCVD) precursors Zr(acac)4 and Zr(dpm)4 (acac = acetylacetonate; dpm = dipivaloylmethanate) as well as a new, highly volatile, air- and moisture-stable Zr precursor based on a tetradentate Schiff-base ligand, Zr(tfacen)2 (tfacen = bis-trifluoroacetylacetone-ethylenediiminate). The improved one-step synthetic routes employ tetrakis(dimethylamido)zirconium as a common intermediate and represent a major advance over previous methods employing ZrCl4 or diketonate metathesis. Furthermore, Zr(tfacen)2 is shown to be an effective metal-organic precursor for the MOCVD-mediated growth of (100) oriented yttria-stabilized zirconia thin films.

The nonlinear optical properties of epitaxial KNbO3 were studied for films grown by metalorganic chemical vapor deposition on different substrates. X-ray diffraction revealed epitaxial KNbO3 with a (110) orientation for layers deposited on single crystal strontium titanate. Whereas, films grown on (100) spinel exhibited a multi-variant structure, consisting of the (110) and (001) orientations. The volume fraction of each crystallographic variant in the film was calculated. Second harmonic generation measurements at 532 nm were performed to determine the ferroelectric domain variants present. The Maker-fringe technique was employed to obtain the effective nonlinear optical susceptibility of the films, which ranged from 0.1 - 1.8 pm/V. The SHG intensity profiles reveal a strong dependence upon substrate type.