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Organic semiconductors are solids whose building blocks are pi-bonded molecules or polymers made up by carbon and hydrogen atoms and — at times — heteroatoms such as nitrogen , sulfur and oxygen.
They exist in form of molecular crystals or amorphous thin films. In general, they are electrical insulators , but become semiconducting when charges are either injected from appropriate electrodes , upon doping or by photoexcitation.
In molecular crystals the energetic separation between the top of the valence band and the bottom conduction band , i. This implies that they are, in fact, insulators rather than semiconductors in the conventional sense. They become semiconducting only when charge carriers are either injected from the electrodes or generated by intentional or unintentional doping.
Charge carriers can also be generated in the course of optical excitation. It is important to realize, however, that the primary optical excitations are neutral excitons with a Coulomb -binding energy of typically 0.
The reason is that in organic semiconductors their dielectric constants are as low as 3—4. This impedes efficient photogeneration of charge carriers in neat systems in the bulk. Efficient photogeneration can only occur in binary systems due to charge transfer between donor and acceptor moieties. Otherwise neutral excitons decay radiatively to the ground state — thereby emitting photoluminescence — or non-radiatively.
The optical absorption edge of organic semiconductors is typically 1. In , Henry Letheby obtained a partly conductive material by anodic oxidation of aniline in sulfuric acid. The material was probably polyaniline. In particular, high conductivity of 0. The fact that organic semiconductors are, in principle, insulators but become semiconducting when charge carriers are injected from the electrode s was discovered by Kallmann and Pope.
This work was stimulated by the earlier discovery by Akamatu et al. Since it was readily realized that the crucial parameter that controls injection is the work function of the electrode, it was straightforward to replace the electrolyte by a solid metallic or semiconducting contact with an appropriate work function. When both electrons and holes are injected from opposite contacts, they can recombine radiatively and emit light electroluminescence.
It was observed in organic crystals in by Sano et al. In Dr. John McGinness produced the first device incorporating an organic semiconductor. This occurred roughly eight years before the next such device was created.
The " melanin polyacetylenes bistable switch" currently is part of the chips collection of the Smithsonian Institution. In , Shirakawa et al. Rigid-backbone organic semiconductors are now used as active elements in optoelectronic devices such as organic light-emitting diodes OLED , organic solar cells , organic field-effect transistors OFET , electrochemical transistors and recently in biosensing applications.
Organic semiconductors have many advantages, such as easy fabrication, mechanical flexibility, and low cost. The discovery by Kallman and Pope paved the way for applying organic solids as active elements in semiconducting electronic devices, such as organic light-emitting diodes OLEDs that rely on the recombination of electrons and hole injected from "ohmic" electrodes, i. Another milestone towards the development of organic light-emitting diodes OLEDs was the recognition that also conjugated polymers can be used as active materials.
Work on conductivity of anthracene crystals contacted with an electrolyte showed that optically excited dye molecules adsorbed at the surface of the crystal inject charge carriers.
This effect revolutionized electrophotography, which is the technological basis of today's office copying machines. Doping with strong electron donor or acceptors can render organic solids conductive even in the absence of light. Examples are doped polyacetylene  and doped light-emitting diodes. Amorphous molecular films are produced by evaporation or spin-coating.
Illustrative materials are tris 8-hydroxyquinolinato aluminium , C 60 , phenyl-Cbutyric acid methyl ester PCBM , pentacene , carbazoles , and phthalocyanine. Molecularly doped polymers are prepared by spreading a film of an electrically inert polymer, e. Typical materials are the triphenylenes. They have been investigated for use as photoreceptors in electrophotography. In the early days of fundamental research into organic semiconductors the prototypical materials were free-standing single crystals of the acene family, e.
This is of particular advantage for OFET applications. Examples are thin films of crystalline rubrene prepared by hot wall epitaxy. They are usually processed from solution employing variable deposition techniques including simple spin-coating, ink-jet deposition or industrial reel-to-reel coating which allows preparing thin films on a flexible substrate. The materials of choice are conjugated polymers such as poly-thiophene, poly-phenylenevinylene, and copolymers of alternating donor and acceptor units such as members of the poly carbazole-dithiophene-benzothiadiazole PCDTBT family.
Aromatic short peptides self-assemblies are a kind of promising candidate for bioinspired and durable nanoscale semiconductors. Therefore, this family of electroactive supramolecular materials may bridge the gap between the inorganic semiconductor world and biological systems. To design and characterize organic semiconductors used for optoelectronic applications one should first measure the absorption and photoluminescence spectra using commercial instrumentation.
However, in order to find out if a material acts as an electron donor or acceptor one has to determine the energy levels for hole and electron transport. The easiest way of doing this, is to employ cyclic voltammetry. However, one has to take into account that using this technique the experimentally determined oxidation and reduction potential are lower bounds because in voltammetry the radical cations and anions are in a polar fluid solution and are, thus, solvated. Such a solvation effect is absent in a solid specimen.
The relevant technique to energetically locate the hole transporting states in a solid sample is UV-photoemission spectroscopy. The equivalent technique for electron states is inverse photoemission.
There are several techniques to measure the mobility of charge carriers. The traditional technique is the so-called time of flight TOF method. Since this technique requires relatively thick samples it is not applicable to thin films. Alternatively, one can extract the charge carrier mobility from the current flowing in a field effect transistor as a function of both the source-drain and the gate voltage. One should be aware, though, that the FET-mobility is significantly larger than the TOF mobility because of the charge carrier concentration in the transport channel of a FET see below.
Other ways to determine the charge carrier mobility involves measuring space charge limited current SCLC flow and "carrier extraction by linearly increasing voltage CELIV. In contrast to organic crystals investigated in the s, organic semiconductors that are nowadays used as active media in optoelectronic devices are usually more or less disordered.
Combined with the fact that the structural building blocks are held together by comparatively weak van der Waals forces this precludes charge transport in delocalized valence and conduction bands. Instead, charge carriers are localized at molecular entities, e.
Quite often the site energies feature a Gaussian distribution. Also the hopping distances can vary statistically positional disorder. A consequence of the energetic broadening of the density of states DOS distribution is that charge motion is both temperature and field dependent and the charge carrier mobility can be several orders of magnitude lower than in an equivalent crystalline system.
This disorder effect on charge carrier motion is diminished in organic field-effect transistors because current flow is confined in a thin layer. Therefore, the tail states of the DOS distribution are already filled so that the activation energy for charge carrier hopping is diminished. For this reason the charge carrier mobility inferred from FET experiments is always higher than that determined from TOF experiments.
In organic semiconductors charge carriers couple to vibrational modes and are referred to as polarons. Therefore, the activation energy for hopping motion contains an additional term due to structural site relaxation upon charging a molecular entity. It turns out, however, that usually the disorder contribution to the temperature dependence of the mobility dominates over the polaronic contribution.
From Wikipedia, the free encyclopedia. Chasseau; G. Comberton; J. Gaultier; C. Hauw Acta Crystallographica Section B. Bibcode : Natur. Bibcode : JChPh..
Journal de Physique Lettres. Bibcode : Sci Journal of the Chemical Society, Chemical Communications 16 : Retrieved Keiji; Gardini, Gian Piero Journal of the Chemical Society, Chemical Communications 14 : Physical Review Letters.
Bibcode : PhRvL.. Bibcode : ApPhL.. Organic Photoreceptors for Xerography. Marcel Dekker Inc. New York. Bibcode : RvMP Electronic processes in organic crystals and polymers. Oxford Science Publications. Physica Status Solidi A. Nature Communications. Bibcode : NatCo Electronic Processes in organic semiconductors.
Wiley — VCH.
Not a MyNAP member yet? Register for a free account to start saving and receiving special member only perks. Materials as a field is most commonly represented by ceramics, metals, and polymers. While noted improvements have taken place in the area of ceramics and metals, it is the field of polymers that has experienced an explosion in progress. Polymers have gone from being cheap substitutes for natural products to providing high-quality options for a wide variety of applications.
Once production of your article has started, you can track the status of your article via Track Your Accepted Article. Help expand a public dataset of research that support the SDGs. Organic Electronics is a journal whose primary interdisciplinary focus is on materials and phenomena related to organic and hybrid organic-inorganic devices such as light emitting diodes, thin film transistors, photovoltaic cells, sensors , memories, etc. Papers suitable for publication in this journal cover such topics as photoconductive and electronic properties of organic and hybrid organic-inorganic materials, thin film structures and characterization in the context of materials processing, charge and exciton transport, and electronic and optoelectronic devices. Organic Electronics provides the forum for applied, fundamental and interdisciplinary contributions spanning the wide range of electronic properties and applications of organic and hybrid organic-inorganic materials. A Letters section is included for rapid publication of short articles announcing significant and highly original results.
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The Materials Science of Semiconductors pp Cite as. One of the most exciting opportunities in optoelectronics currently is devices based on organic materials.
Materials, Physics, Chemistry and Applications
Par hellwig marvin le samedi, juillet 23 , - Lien permanent. Electronic processes in organic crystals and polymers Pope M. Publisher: OUP. And just as the semiconductor industry is actively developing smaller and smaller transistors, so, too, are those involved with organic electronics devising ways to shrink the features of their materials, so they can be better utilized in bioelectronic applications such as those above. The book was translated into Russian and also was distributed in China. Moreover, the charge transport mechanisms in conjugated polymers and the.. The first edition of Pope and Swenberg's Electronic Processes of Organic Crystals, published in , became the classic reference in the field.
Skip to search form Skip to main content You are currently offline. Some features of the site may not work correctly. Pope and C. Pope , C. Swenberg Published Materials Science.
Organic semiconductors are solids whose building blocks are pi-bonded molecules or polymers made up by carbon and hydrogen atoms and — at times — heteroatoms such as nitrogen , sulfur and oxygen. They exist in form of molecular crystals or amorphous thin films. In general, they are electrical insulators , but become semiconducting when charges are either injected from appropriate electrodes , upon doping or by photoexcitation. In molecular crystals the energetic separation between the top of the valence band and the bottom conduction band , i. This implies that they are, in fact, insulators rather than semiconductors in the conventional sense. They become semiconducting only when charge carriers are either injected from the electrodes or generated by intentional or unintentional doping. Charge carriers can also be generated in the course of optical excitation.
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