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Organic semiconductor

About: Organic semiconductor is a research topic. Over the lifetime, 15905 publications have been published within this topic receiving 533881 citations.


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TL;DR: In this paper, a model to explain the electrical bistability of two-terminal electrical devices is proposed, where the nanostructure of the middle metal layer is incorporated with metal nanoclusters separated by thin oxide layers.
Abstract: Two-terminal electrical bistable devices have been fabricated using a sandwich structure of organic/metal/organic as the active medium, sandwiched between two external electrodes. The nonvolatile electrical bistability of these devices can be controlled using a positive and a negative electrical bias alternatively. A forward bias may switch the device to a high-conductance state, while a reverse bias is required to restore it to a low-conductance state. In this letter, a model to explain this electrical bistability is proposed. It is found that the bistability is very sensitive to the nanostructure of the middle metal layer. For obtaining the devices with well-controlled bistability, the middle metal layer is incorporated with metal nanoclusters separated by thin oxide layers. These nanoclusters behave as the charge storage elements, which enable the nonvolatile electrical bistability when biased to a sufficiently high voltage. This mechanism is supported by the experimental data obtained from UV–visible ...

371 citations

Journal ArticleDOI
TL;DR: Results demonstrate that variation of the alkyl chain branching point is a powerful strategy for tuning of molecular packing to enable high charge transport mobilities.
Abstract: Substituted side chains are fundamental units in solution processable organic semiconductors in order to achieve a balance of close intermolecular stacking, high crystallinity, and good compatibility with different wet techniques. Based on four air-stable solution-processed naphthalene diimides fused with 2-(1,3-dithiol-2-ylidene)malononitrile groups (NDI-DTYM2) that bear branched alkyl chains with varied side-chain length and different branching position, we have carried out systematic studies on the relationship between film microstructure and charge transport in their organic thin-film transistors (OTFTs). In particular synchrotron measurements (grazing incidence X-ray diffraction and near-edge X-ray absorption fine structure) are combined with device optimization studies to probe the interplay between molecular structure, molecular packing, and OTFT mobility. It is found that the side-chain length has a moderate influence on thin-film microstructure but leads to only limited changes in OTFT performanc...

370 citations

Journal ArticleDOI
TL;DR: In this paper, a semitransparent metal electrode fabricated by nano-imprint lithography (NIL) was evaluated as an anode material for OLED anodes and evaluated its potential as anodes.
Abstract: Organic light-emitting diodes (OLEDs) are promising for full-color, full-motion, flat panel display applications because they offer several advantageous features, for example, ease of fabrication, low costs, light weight, bright self-emission, a wide viewing angle, and the possibility of flexible displays. The basic OLED structure consists of a number of organic semiconductor layers sandwiched between a cathode and an anode. For efficient electron injection into the organic layers, low-work-function materials are required for the cathode. A very thin LiF layer with a thick Al capping is widely used for this purpose. For the anode, indium tin oxide (ITO) is the predominant choice because it offers transparency in the visible range of the electromagnetic spectrum as well as electrical conductivity. However, several aspects of ITO are far from optimal for high-performance OLEDs. It is known that the migration of indium and oxygen from ITO into organic semiconductors during OLED operation causes device degradation. The electrical properties of ITO greatly depend on the film preparation. The rough surface of the deposited ITO film and the work function of ITO, ca. 4.7 eV, limit the efficiency of the hole injection. The typical sheet resistance of a 100 nm thick ITO layer, 20–80 X/ , is still high, which causes a voltage drop along the addressing line, thus limiting the operation of a large-area passive matrix OLED array. Moreover, the cost of ITO has escalated in recent years because of the jump in price of the element indium. Several alternative materials, for example, TiN, Al-doped ZnO, and fluorine tin oxide, have been investigated as anode materials instead of ITO; however, none are optimal as anode in OLEDs because they have either a lower work function or a lower conductivity than ITO. Other transparent conducting oxides, such as Ga–In–Sn–O (GITO), Zn–In–Sn–O (ZITO), Ga–In–O (GIO), and Zn–In–O (ZIO), that have a higher work function and a similar electrical conductivity when compared to ITO have also been examined as OLED anode materials. However, they are potentially problematic because they also contain the element indium that i) may diffuse into the organic layer in the OLED; and ii) has a high price, making these electrodes expensive. Besides these materials several metals with a high work function, such as Au, Ni, and Pt, have been investigated as anodes for OLEDs. In these cases the metal was used to modify the surface of the ITO electrode, or as an anode for top-emitting devices. A surface-modified thin Ag film has been used as a semitransparent electrode instead of ITO, but its transparency was low. Recently, carbon nanotube films have been investigated as transparent, conductive electrodes, but they have a high sheet resistance that may limit the device performance. In this Communication, we report semitransparent metal electrodes fabricated by nanoimprint lithography (NIL), and evaluate their potential as OLED anodes. NIL, an emerging lithographic technique, is well-suited to the area of organic electronics, which requires low-cost and high-throughput fabrication at high resolution. The fabricated semitransparent metal electrode offers several advantages over ITO for OLED applications. First, several problems associated with ITO can be eliminated, such as device degradation by indium diffusion and high costs. Second, efficient hole injection into the organic semiconductor can be realized by choosing metals with a high work function, such as Au or Pt. Third, a semitransparent metal electrode is potentially suitable for topemitting devices and tandem structures. Last, but not least, the output efficiency of the OLED can be enhanced by preventing waveguiding in the ITO layer, which occurs as a result of its high refractive index and is one of the limitations to the external efficiency of OLEDs, and by forming a two-dimensional (2D) hole array with proper periodicity. We demonstrate here that a unique property of such an electrode is that its optical transparency and the electrical conductivity can be tuned separately by changing the aperture ratio and the metal thickness, thereby making it possible to tailor the structures for different applications. To our knowledge, a nanoimprinted semitransparent metal electrode has not been reported before. The semitransparent metal electrodes are in the form of a nanometer-scale periodically perforated dense metal mesh on glass. Two design considerations led to such structures: i) the line width of the metal mesh was designed to be subwavelength, to provide sufficient transparency and to minimize light scattering; and ii) the period of the mesh was chosen to be sub-micrometer to ensure the uniformity of the current injection into the organic semiconductors. Such large-area dense nanostructures can be fabricated by NIL, which is ideal for this application because of its inherently high resolution C O M M U N IC A IO N

370 citations

Journal ArticleDOI
TL;DR: In this paper, a pyrene-based conjugated polymer is synthesized via the typical Suzuki-Miyaura reactions, and then employed as a substrate to anchor CdS nanocrystals.
Abstract: Inspired by natural photosynthesis, constructing inorganic/organic heterojunctions is regarded as an effective strategy to design high-efficiency photocatalysts. Herein, a step (S)-scheme heterojunction photocatalyst is prepared by in situ growth of an inorganic semiconductor firmly on an organic semiconductor. A new pyrene-based conjugated polymer, pyrene-alt-triphenylamine (PT), is synthesized via the typical Suzuki-Miyaura reactions, and then employed as a substrate to anchor CdS nanocrystals. The optimized CdS/PT composite, coupling 2 wt% PT with CdS, exhibits a robust H2 evolution rate of 9.28 mmol h-1 g-1 with continuous release of H2 bubbles, as well as a high apparent quantum efficiency of 24.3%, which is ≈8 times that of pure CdS. The S-scheme charge transfer mechanism between PT and CdS, is systematically demonstrated by photoirradiated Kelvin probe measurement and in situ irradiated X-ray photoelectron spectroscopy analyses. This work provides a protocol for preparing specific S-scheme heterojunction photocatalysts on the basis of inorganic/organic coupling.

369 citations

Journal ArticleDOI
TL;DR: In this article, the formation of the metal-organic contact and the parameters which control the injection current are discussed, as well as the origins of the vacuum level offset, which is not yet fully understood.
Abstract: Charge injection at the interface between metallic electrodes and organic semiconductors plays a crucial role in the performance of organic (opto-)electronic devices. This article discusses the current understanding of the formation of the metal–organic contact and the parameters which control the injection current. Organic semiconductors differ significantly from their inorganic counterparts, primarily because they are amorphous van der Waals solids. As a result the electronic states are highly localized, and charge transport is by site-to-site hopping. Organics can also form clean interfaces with many metals, free of interface states in the gap. Nevertheless, there is generally found to be a significant vacuum level offset, the origins of which are not yet fully understood. Organic semiconductors are frequently free of donor and acceptor dopants, and as a result the depletion depth is larger than the organic layer thickness. Thus the Fermi level in the organic and the charge injection barriers depend mo...

368 citations


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Performance
Metrics
No. of papers in the topic in previous years
YearPapers
2023258
2022558
2021580
2020697
2019701
2018713