Interface dipole engineering at buried organic–organic semiconductor heterojunctions

A general technique for modifying energy level alignment at organic–organic heterojunctions is introduced, and is demonstrated here for phenyl-C₆₁-butyric acid methyl ester (PCBM) and N,N′-Di-[(1-naphthyl)-N,N′-diphenyl]-1,1′-biphenyl)-4,4′-diamine (α-NPD). An ultra-thin layer (∼1 nm) of TiO₂ is used as an adhesion template to attach a self-assembled monolayer of dipolar phosphonate (PA) molecules to the lower interface of a two-stack ensemble. This modification induces shifts in the vacuum level and work function over ∼1.0 eV depending on the molecular dipole moment of the PA, which in turn modifies the electronic level alignment across the organic heterojunction interface by up to 0.5 eV.     

The Influence of Film Morphology in High‐Mobility Small‐Molecule:Polymer Blend Organic Transistors

Organic field‐effect transistors (OFETs) based upon blends of small molecular semiconductors and polymers show promise for high performance organic electronics applications. Here the charge transport characteristics of high mobility p‐channel organic transistors based on 2,8‐difluoro‐5,11‐bis(triethylsilylethynyl) anthradithiophene:poly(triarylamine) blend films are investigated. By simple alteration of the film processing conditions two distinct film microstructures can be obtained: one characterized by small spherulitic grains (SG) and one by large grains (LG). Charge transport measurements reveal thermally activated hole transport in both SG and LG film microstructures with two distinct temperature regimes. For temperatures >115 K, gate voltage dependent activation energies (E_A) in the range of 25–60 meV are derived. At temperatures <115 K, the activation energies are smaller and typically in the range 5–30 meV. For both film microstructures hole transport appears to be dominated by trapping at the grain boundaries. Estimates of the trap densities suggests that LG films with fewer grain boundaries are characterized by a reduced number of traps that are less energetically disordered but deeper in energy than for small SG films. The effects of source and drain electrode treatment with self‐assembled monolayers (SAMs) on current injection is also investigated. Fluorinated thiol SAMs were found to alter the work function of gold electrodes by up to ～1 eV leading to a lower contact resistance. However, charge transport analysis suggests that electrode work function is not the only parameter to consider for efficient charge injection.     

新型自振荡电源转换器VK05CFL

1.技术概述 VK05CFL是一种用于驱动微型荧光灯的自振荡转换器,采用意法半导体的VIPower M3-3专利技术制造而成,允许在同一芯片上集成控制部分和电源级。电源级是一个“发射器开关”,其构成是在级联配置内放置一个双极高压复合晶体管和一个低压MOSFET,因此,在高击穿电     

Impact of Blend Morphology on Interface State Recombination in Bulk Heterojunction Organic Solar Cells

This work is a reinvestigation of the impact of blend morphology and thermal annealing on the electrical performance of regioregular‐P3HT:PC₆₀BM bulk heterojunction organic solar cells. The morphological, structural, and electrical properties of the blend are experimentally investigated with atomic force microscopy, X‐ray diffraction, and time‐of‐flight measurements. Current–voltage characteristics of photodiode devices are measured in the dark and under illumination. Finally, the existence of exponential electronic band tails due to gap states is experimentally confirmed by measuring the device spectral response in the subband gap regime. This method reveals the existence of a large density of gap states, which is partially and systematically reduced by thermal annealing. When the band tails are properly accounted for in the drift and diffusion simulations, experimentally measured charge transport characteristics, under both dark and illuminated conditions and as a function of annealing time, can be satisfactorily reproduced. This work further confirms the critical impact of tails states on the performance of solar cells.     

Doping Molecular Monolayers: Effects on Electrical Transport Through Alkyl Chains on Silicon

n‐Si/C_nH_{2n + 1}/Hg junctions (n = 12, 14, 16 and 18) can be prepared with sufficient quality to assure that the transport characteristics are not anymore dominated by defects in the molecular monolayers. With such organic monolayers we can, using electron, UV and X‐ray irradiation, alter the charge transport through the molecular junctions on n‐ as well as on p‐type Si. Remarkably, the quality of the self‐assembled molecular monolayers following irradiation remains sufficiently high to provide the same very good protection of Si from oxidation in ambient atmosphere as provided by the pristine films. Combining spectroscopic (UV photoemission spectroscopy (UPS), X‐ray photoelectron spectroscopy (XPS), Auger, near edge‐X‐ray absorption fine structure (NEXAFS)) and electrical transport measurements, we show that irradiation induces defects in the alkyl films, most likely C?C bonds and C? C crosslinks, and that the density of defects can be controlled by irradiation dose. These altered intra‐ and intermolecular bonds introduce new electronic states in the highest occupied molecular orbital (HOMO)–lowest unoccupied molecular orbital (LUMO) gap of the alkyl chains and, in the process, dope the organic film. We demonstrate an enhancement of 1–2 orders of magnitude in current. This change is clearly distinguishable from the previous observed difference between transport through high quality and defective monolayers. A detailed analysis of the electrical transport at different temperatures shows that the dopants modify the transport mechanism from tunnelling to hopping. This study suggests a way to extend significantly the use of monolayers in molecular electronics.     

Tailoring Electron‐Transfer Barriers for Zinc Oxide/C60 Fullerene Interfaces

The interfacial electronic structure between oxide thin films and organic semiconductors remains a key parameter for optimum functionality and performance of next‐generation organic/hybrid electronics. By tailoring defect concentrations in transparent conductive ZnO films, we demonstrate the importance of controlling the electron transfer barrier at the interface with organic acceptor molecules such as C₆₀. A combination of electron spectroscopy, density functional theory computations, and device characterization is used to determine band alignment and electron injection barriers. Extensive experimental and first principles calculations reveal the controllable formation of hybridized interface states and charge transfer between shallow donor defects in the oxide layer and the molecular adsorbate. Importantly, it is shown that removal of shallow donor intragap states causes a larger barrier for electron injection. Thus, hybrid interface states constitute an important gateway for nearly barrier‐free charge carrier injection. These findings open new avenues to understand and tailor interfaces between organic semiconductors and transparent oxides, of critical importance for novel optoelectronic devices and applications in energy‐conversion and sensor technologies.     

The behavior of chromium and molybdenum in the propagation process of localized corrosion of steels

In order to clarify the effect of Cr and Mo on the propagation of localized corrosion of steels, the electrochemical behavior of pure chromium and molybdenum and of some stainless steels was studied under conditions similar to those existing inside occluded corrosion cells of steels. Oxygen-free FeCl₂ and/or CrCl₃ solutions were used for experiments. The surface films formed in these conditions were analyzed by means of AES and XPS. Cr is passive if the pH value >ca. 1.8 and Cr may retard the propagation of localized corrosion of steels in its early stage. The hydrolysis of Cr³⁺ may change the pH to even lower values. At such low pH and high Cl^? concentrations, Cr is active in the potential range of interest for localized corrosion of steels. Mo is passive under these more acidic conditions and the passivity of Mo in this potential range is attributed to the formation of a film of MoO₂ (or hydrated oxide), which is extremely thin but very protective. Mo is thus effective to retard the propagation of localized corrosion of steels in its more advanced stage.     

Interfacial bonding of Flax fibre/Poly(l-lactide) bio-composites

The use of glass fibre reinforced polyester composites raises many health and safety and environmental questions. One alternative is the development of high performance bio-based bio-composites with low environmental impact. Improved understanding of interfacial properties is essential to optimise the mechanical properties and durability of these materials, but so far few data are available. The present work describes the interfacial characterization of Flax fibre/Poly(lactic) acid (PLLA) system at the micro-scale using the microbond test. Different thermal treatments have been carried out (cooling rate and annealing) in order to evaluate the influence of matrix and interfacial morphologies as well as residual stress on interfacial properties. Micromechanical models have been used to determine the interfacial shear strength. When cooling rate is slow, improved interfacial properties are observed.     

PLLA/Flax Mat/Balsa Bio-Sandwich—Environmental Impact and Simplified Life Cycle Analysis

In the present paper the environmental impact of biocomposites and bio-sandwich materials production are evaluated, using simplified Life Cycle Analysis (LCA) following the procedure recommended in the ISO 14044 standard. The materials are dimensioned and evaluated by comparing with reference materials, glass mat reinforced unsatured polyester and glass mat/unsatured polyester/balsa sandwich. The results indicate that bio-sandwich materials are very attractive in terms environmental impact. However further improvements in biocomposite and bio-sandwich mechanical strength are necessary if they are to be used in transport application compared to glass/polyester and glass/polyester/balsa sandwich.