Ambipolar Semiconductors Research Articles

The lower rather than higher density charge carrier determines the NH3-sensing nature and sensitivity of ambipolar organic semiconductors

NH3 sensing behavior from ambiplolar bisphthalocyanines manifests the lower density carrier (hole vs. electron) with faster charge transporting speed in semiconducting layer in determining the sensing response nature.

Photoelectrochemical processes in organic semiconductor: Ambipolar perylene diimide thin film

A thin film of N,N′-dioctadecyl-3,4,9,10-perylene tetracarboxylic diimide (PTCDI-C18) is spin-coated on indium tin oxide (ITO) glass. Using the PTCDI-C18/ITO electrode, we fabricate a photoelectrochemical cell with the ITO/PTCDI-C18/Redox Electrolyte/Pt configuration. The electrochemical properties of this device are investigated as a function of hydroquinone (HQ) concentration, bias voltage, and wavelength of light. Anodic photocurrent is observed at V ≥ −0.2 V vs. Ag/AgCl, indicating that the PTCDI-C18 film acts as an n-type semiconductor as usual. However, when benzoquinone (BQ) is inserted into the electrolyte system instead of HQ, cathodic photocurrent is observed at V ≤ 0.0 V, displaying that PTCDI-C18 abnormally serves as a p-type semiconductor. Hence the overall results reveal that the PTCDI-C18 film can be an ambipolar functional semiconductor depending on the redox couple in the appropriate voltage.

Virtual Design in Organic Electronics: Screening of a Large Set of 1,4-Bis(phenylethynyl)benzene Derivatives as Molecular Semiconductors

In this work, we have theoretically studied the electronic properties of a large series of 1,4-bis(phenylethynyl)benzene derivatives, with the chemical formula Y–C≡C–X–C≡C–Y, with X and Y being aromatic rings and chosen to act as donor and acceptor moieties. Employing state-of-the-art DFT calculations, we analyzed a set of relevant electronic properties related to the optoelectronic and semiconductor character of these systems, namely, molecular and energy levels, electron affinity, ionization potential, reorganization energy, and electronic coupling between neighboring molecules forming dimers, obtained after evaluation of binding energy landscapes. The latter energy magnitude is needed to disclose first the favored intermolecular interactions (i.e., the lowest binding energy) to concomitantly estimate next the charge transport rates. The systematic screening performed allowed us to anticipate the possible use of some of these derivatives as p-type, n-type, or even ambipolar organic molecular semiconductors.

Theoretical studies on the effect of benzene and thiophene groups on the charge transport properties of Isoindigo and its derivatives

In this work, the charge transport properties of Isoindigo (II) and its derivatives which have the same hexyl chain were theoretically investigated by the Marcus-Hush theory combined with density functional theory (DFT). Here we demonstrate that the changes of benzene and thiophene groups in molecular structure have an important influence on the charge transport properties of organic semiconductor. The benzene rings of II are replaced by thiophenes to form the thienoisoindigo (TII), and the addition of benzene rings to the TII form the benzothienoisoindigo (BTII). The results show that benzene rings and thiophenes change the chemical structure of crystal molecules, which lead to different molecule stacking, thus, the length of hydrogen bond was changed. A shorter intermolecular hydrogen bond lead to tighter molecular stacking, which reduces the center-to-center distance and enhances the ability of charge transfer. At the same time, we theoretically demonstrated that II and BTII are the ambipolar organic semiconductor. BTII has better carrier mobility. The hole mobility far greater than electron mobility in TII, which is p-type organic semiconductor. Among all hopping path, we find that the distance of face-to-face stacking in II is the shortest and the electron-transport electronic coupling V e is the largest, but II has not a largest anisotropic mobility, because the reorganization energy has a greater influence on the mobility than the electronic coupling. This work is helpful for designing ambipolar organic semiconductor materials with higher charge transport properties by introducing benzene ring and thiophene.

Synthesis, fabrication of self-assembled film and ambipolar chemical sensing properties of triple-decker (phthalocyaninato) (porphyrinato) europium complex

A mixed (phthalocyaninato) (porphyrinato) europium triple-decker complex, named (TPyP)Eu[Formula: see text][Pc(OC[Formula: see text]H[Formula: see text]][Formula: see text][TPyP [Formula: see text] dianion of 5,10,15,20-tetra(4-tert-pyridyl) porphyrin, Pc(OC[Formula: see text]H[Formula: see text] 2,3,9,10,16,17,23,24-octabutoxyphthalocyaninate] is synthesized and characterized by MALDI-TOF, 1HNMR, UV-visible spectra and differential pulse voltammetry techniques. Introduction of electron-donating butoxy groups at the periphery of the phthalocyanine ligands and electron-withdrawing pyridyl substituents onto the meso-positions of the porphyrin ring not only increases the solubility of the triple decker but successfully tunes the HOMO and LUMO energy levels into a soluble ambipolar organic semiconductor. A simple quasi-Langmuir–Shäfer (QLS) method is used to fabricate self-assembled film of (TPyP)Eu[Formula: see text][Pc(OC[Formula: see text]H[Formula: see text]][Formula: see text]. Excellent sensitivity, reproducible [Formula: see text]-type and [Formula: see text]-type responses to electron-accepting gas NO[Formula: see text] and electron-donating gas NH[Formula: see text] are found for the films of (TPyP)Eu[Formula: see text][Pc(OC[Formula: see text]H[Formula: see text]][Formula: see text]complex at room temperature. The detection limit towards NO[Formula: see text] and NH[Formula: see text] is as low as 0.4 ppm and 1 ppm, respectively, with percentage current change of 4.2% and 1.6%, depending on the uniform molecular packing and intermolecular interactions among the triple decker molecules. The present results represent not only the excellent example of ambipolar triple-decker phthalocyanine-based sensors obtained by a solution-based method, but more importantly provide a new strategy for the molecular design to obtain soluble ambipolar organic semiconductors in sensing device fabrication.

Thiophene-Fused Naphthalene Diimides: New Building Blocks for Electron Deficient π-Functional Materials

Abstract Development of novel π-conjugated building blocks that can be integrated into molecular or macromolecular systems is key to the evolution of new superior organic semiconductors utilized as the active materials in organic electronics devices such as organic field-effect transistors (OFETs), organic photovoltaics (OPVs), and organic thermoelectric (TE) devices. This review affords a brief overview of thiophene-fused naphthalene diimide (NDI), namely naphtho[2,3-b:6,7-b′]dithiophene diimide (NDTI) and naphtho[2,3-b]thiophene diimide (NTI), recently developed as novel electron deficient building blocks for n-type and ambipolar organic semiconductors. These thiophene-fused NDI building blocks had not been known until 2013 owing to their synthetic difficulty; more precisely, the difficulty in attaching fused-thiophene ring(s) on the NDI core. We have successfully established a thiophene-annulation reaction on ethyne-substituted NDI derivatives, which allows us to elaborate various NDTI and NTI derivatives. The key features of these building blocks are low-lying energy levels of lowest unoccupied molecular orbitals (LUMO, 3.8–4.1 eV below the vacuum level) and easy functionalizability of the thiophene α-positions, which allows their derivatives and polymers to conjugate efficiently with additional π- and co-monomer units. These features make the NDTI- and NTI-derivatives and polymers promising n-type and ambipolar materials for OFETs and acceptors for OPVs. In fact, various useful materials have already been derived from the NDTI and NTI building blocks: air-stable n-type small molecules and polymers with high electron mobility (∼0.8 cm2 V−1 s−1), ambipolar oligomers and polymers with well-balanced hole and electron mobilities, doped n-type semiconductors affording bulk conductors applicable to n-type TE materials, and electron acceptor molecules and polymers for OPVs showing promising power conversion efficiencies of up to 9%. These impressive and diversified device performances testify the usefulness of thiophene-fused NDI building blocks in the development of new electron deficient π-functional materials.

An approach to discovering novel exciplex supramolecular complex based on carbazole-containing 1,8-naphthalimide

A new luminescent ambipolar semiconductor consisting of 1,8-naphthalimide as an electron-accepting moiety and carbazole as an electron-donating moiety has been synthesized and characterized. The synthesized compound as ambipolar semiconductor has been investigated by using density functional theory calculations coupled with the charge-hopping model and the time-of-flight experimental method. The time-of-flight hole and electron drift mobilities in the synthesized material's layer approached about 10−4 cm2 V−1 s−1 at high electric fields. The exciplex complex is stabilized by the intermolecular hydrogen bond and electron donor-acceptor interactions. The energy of interactions between the molecules in the exciplex complex has been estimated to be about −100 kJ mol−1 by DFT. Non-doped emissive layer organic light-emitting diode (OLED) using the synthesized compound as an emitter exhibited an orange color emission with the Commission International de L'Eclairage chromaticity coordinates of (0.47, 0.49).

Ambipolar chemical sensors based on the self-assembled film of an amphiphilic (phthalocyaninato) (porphyrinato) europium complex

An amphiphilic mixed (phthalocyaninato) (porphyrinato) europium triple-decker complex Eu2(Pc)2(TPyP) has been synthesized and characterized. Introducing electron-withdrawing pyridyl substituents onto the meso-position of porphyrin ring in the triple-decker to ensure the sufficient hydrophilicity and suitable HOMO and LUMO energy levels and thus successfully realize amphiphilic ambipolar organic semiconductor. Importantly, high sensitive, reproducible p-type and n-type responses towards NH3 and NO2 respectively, based on the self-assembled film of the Eu2(Pc)2(TPyP) fabricated by a simple solution-based Quasi–Langmuir–Shäfer (QLS) method, have been first revealed. The good conductivity and crystallinity for the QLS film of Eu2(Pc)2(TPyP) render it excellent sensing property for both electron-donating gas NH3 in 5–30ppm range and electron-accepting gas NO2 in 400–900ppb range due to the optimized molecular packing in the uniform-sized nanoparticles depending on the effective intermolecular interaction between the triple-decker molecules, among the best results of phthalocyanine-based chemical sensors for room-temperature detection of NH3 and NO2, respectively. Furthermore, the responses of the QLS film are all linearly correlated to both NH3 and NO2 with excellent sensitivity of 0.04%ppm−1 and 31.9%ppm−1, respectively, indicating the great potential of semiconducting tetrapyrrole rare earth triple-decker compounds in the field of chemical sensors.

Density functional theory calculations of charge transport properties of ‘plate-like’ coronene topological structures

Charge transport rate is one of the key parameters determining the performance of organic electronic devices. In this paper, we used density functional theory (DFT) at the M06-2X/6−31 $$+$$ G(d) level to compute the charge transport rates of nine coronene topological structures. The results show that the energy gap of these nine coronene derivatives is in the range 2.90–3.30 eV, falling into the organic semiconductor category. The size of the conjugate ring has a large influence on the charge transport properties. Incorporation of methyl groups on the rigid core of tetrabenzocoronene and hexabenzocoronene is more conducive to the hole transport of the molecule than incorporating methoxyl groups. The derivatisation of a ‘long plate-like’ coronene with methoxyl groups facilitates both hole and electron transport. This class of molecules can thus be used in the design of ambipolar transport semiconductor materials. JCSC-D-16-01407 SYNOPSIS Density functional theory was used to compute the charge transport rates of three series nine coronene topological structures at the M06-2X/6−31+G(d) level. Tetrabenzocoronene (series a) and hexabenzocoronene (series b) could be candidates for a hole-transporting (p-type) organic semiconductor material, and ‘long plate-like’ coronene topological structures (series c) could be used as an ambipolar transport material.

Isoindigo-Based Polymers with Small Effective Masses for High-Mobility Ambipolar Field-Effect Transistors.

So far, most of the reported high-mobility conjugated polymers are p-type semiconductors. By contrast, the advances in high-mobility ambipolar polymers fall greatly behind those of p-type counterparts. Instead of unipolar p-type and n-type materials, ambipolar polymers, especially balanced ambipolar polymers, are potentially serviceable for easy-fabrication and low-cost complementary metal-oxide-semiconductor circuits. Therefore, it is a critical issue to develop high-mobility ambipolar polymers. Here, three isoindigo-based polymers, PIID-2FBT, P1FIID-2FBT, and P2FIID-2FBT are developed for high-performance ambipolar organic field-effect transistors. After the incorporation of fluorine atoms, the polymers exhibit enhanced coplanarity, lower energy levels, higher crystallinity, and thus increased µe . P2FIID-2FBT exhibits n-type dominant performance with a µe of 9.70 cm2 V-1 s-1 . Moreover, P1FIID-2FBT exhibits a highly balanced µh and µe of 6.41 and 6.76 cm2 V-1 s-1 , respectively, which are among the highest values for balanced ambipolar polymers. Moreover, a concept "effective mass" is introduced to further study the reasons for the high performance of the polymers. All the polymers have small effective masses, indicating good intramolecular charge transport. The results demonstrate that high-mobility ambipolar semiconductors can be obtained by designing polymers with fine-tuned energy levels, small effective masses, and high crystallinity.

An aromatic amine-containing polymer as an additive to ambipolar polymer semiconductor realizing unipolar n-type charge transport

Abstract We report the synthesis of an aromatic amine-containing polymer (PDPAT-12) and the use of this polymer as an effective additive to an ambipolar polymer semiconductor (PIBDFBT-e37) to realize unipolar n-type charge transport in organic thin film transistors (OTFTs). With 10 wt% PDPAT-12 addition to PIBDFBT-e37, the OTFTs achieved unipolar n-type charge transport with electron mobility of up to 0.42 cm2 V−1 s−1 in nitrogen and 0.19 cm2 V−1 s−1 in air. Moreover, the polymer blend demonstrated improved stability towards ambient air (retaining 50% of its initial electron mobility after exposed in air for 28 days) than the pristine PIBDFBT-e37 (retaining 13% of its initial electron mobility under the same conditions) and the PIBDFBT-e37:PEI (polyethylenimine) blend, which lost transistor behaviour almost instantly once exposed to ambient air. Our results show that the use of this aromatic amine-containing polymer as an additive can convert an ambipolar polymer into an n-type unipolar polymer in OTFTs with much improved air stability.

An efficient strategy for designing ambipolar organic semiconductor material: Introducing dehydrogenated phosphorus atoms into pentacene core

The charge transport properties of phosphapentacene (P-PEN) derivatives were systematically explored by theoretical calculation. The dehydrogenated P-PENs have reasonable frontier molecular orbital energy levels to facilitate both electron and hole injection. The reduced reorganization energies of dehydrogenated P-PENs could be intimately connected to the bonding nature of phosphorus atoms. From the idea of homology modeling, the crystal structure of TIPSE-4P-2p is constructed and fully optimized. Fascinatingly, TIPSE-4P-2p shows the intrinsic property of ambipolar transport in both hopping and band models. Thus, introducing dehydrogenated phosphorus atoms into pentacene core could be an efficient strategy for designing ambipolar material.

Multilayer organic photovoltaic devices fabricated by electrospray deposition technique and the role of the interlayer

Multilayer organic photovoltaic (OPV) devices were fabricated using the electrospray deposition method. The film-formation conditions and particularly the solvent composition were investigated to reveal the importance of the boiling point and polarity of the component solvents. The deposited film must be semi-wet to form a flat film by slow-drying at ambient conditions, resulting from the high boiling point and high affinity of o-dichlorobenzene for poly(3-hexylthiophene) (P3HT) and [6,6]-C70-butyric acid methyl ester (PC70BM). On the other hand, a polar solvent assists in the formation of an electrospray with a wide spray range under an applied voltage. Employing the film formation conditions, double-layered (P3HT and PC70BM) and triple-layered (P3HT, interlayer, and PC70BM) OPV devices were fabricated. A diketopyrrolopyrrole derivative, which is a near-infrared-absorbing ambipolar semiconductor, was applied as the interlayer material. By comparing the two devices, it was determined that the interlayer acts as a sensitizer at around 700nm for the P3HT–PC70BM system.

Influence of Asymmetric Contact Form on Contact Resistance and Schottky Barrier, and Corresponding Applications of Diode.

We have fabricated carbon nanotube and MoS2 field-effect transistors with asymmetric contact forms of source-drain electrodes, from which we found the current directionality of the devices and different contact resistances under the two current directions. By designing various structures, we can conclude that the asymmetric electrical performance was caused by the difference in the effective Schottky barrier height (ΦSB) caused by the different contact forms. A detailed temperature-dependent study was used to extract and compare the ΦSB for both contact forms of CNT and MoS2 devices; we found that the ΦSB for the metal-on-semiconductor form was much lower than that of the semiconductor-on-metal form and is suitable for all p-type, n-type, or ambipolar semiconductors. This conclusion is meaningful with respect to the design and application of nanomaterial electronic devices. Additionally, using the difference in barrier height caused by the contact forms, we have also proposed and fabricated Schottky barrier diodes with a current ratio up to 104; rectifying circuits consisting of these diodes were able to work in a wide frequency range. This design avoided the use of complex chemical doping or heterojunction methods to achieve fundamental diodes that are relatively simple and use only a single material; these may be suitable for future application in nanoelectronic radio frequency or integrated circuits.

Roles of 3-Ethylrhodanine in Attaining Highly Ordered Crystal Arrays of Ambipolar Diketopyrrolopyrrole Oligomers.

Until now, only limited DPP oligomers delivered ambipolar semiconductor characteristics. To develop a facile strategy of preparing ambipolar mono-DPP oligomers, two dithienyl diketopyrrolopyrrole (DPPT) based-conjugated molecules, DPPT-RD and DPPT-DCV, which contain 3-ethylrhodanine (RD) and dicyano-2-vinyl (DCV) end substituents were synthesized. The influences of the -RD end substituents on the molecular properties, solid-state morphology, and OFET performances of the DPPT oligomer were investigated. The UV-vis absorption and CV results showed that the RD end substituents provide the DPPT oligomer suitable EHOMO and ELUMO for hole and electron injection from the Au source-drain electrodes. Moreover, the RD end substituents also improve the crystalline nature of the DPPT oligomer. That is, DPPT-RD can form crystal arrays with good lattice orientation, larger crystalline size, and without polymorphism. With those properties, DPPT-RD thus display ambipolar characteristic with μh and μe reaching 2.16 × 10-2 and 7.27 × 10-2 cm2 V-1 s-1, respectively.

Synthesis and Properties of Dicyanomethylene-Endcapped Thienopyrrole-Based Quinoidal S,N-Heteroacenes

Abstract A new series of highly π-extended dicyanomethylene-endcapped quinoidal S,N-heteroacenes (JH-quinoids) fused with thiophene and pyrrole rings have been designed and synthesized. The π-extension of the central S,N-heteroacene cores gives rise to significant red-shifted absorption maxima in solution without being affected by the long alkyl groups. The absorption maximum of JH10 with the longest quinoidal backbone in the thin film significantly red-shifted to the near-infrared region of 1260 nm as compared to that in solution (880 nm), indicating the formation of strong intermolecular interaction in the solid state. JH-quinoids maintain sufficiently low LUMO energy levels in the range of −4.09∼−4.22 eV regardless of the fused ring systems and substituents, while the HOMO energy levels increase with extending the length of S,N-heteroacenes; the highest HOMO energy level of JH10 is as high as −5.18 eV owing to the contributions from the nitrogen atoms and chalcogen. The molecular geometries of JH-quinoids optimized from the DFT calculations indicate their complete planar backbones and the trend of HOMO and LUMO energy levels variation is in good agreement with the cyclic voltammetry results. Consequently, the present JH-quinoids should be promising candidates for ambipolar organic semiconductors.

H-Bonding Control of Supramolecular Ordering of Diketopyrrolopyrroles

Diketopyrrolopyrrole (DPP) is a widely used building block for high-mobility ambipolar semiconductors. Hydrogen bonding of N-unsubstituted DPPs has recently been identified as a tool for controlling their solid state structure and properties of semiconducting films, yet little is known about supramolecular packing of H-bonded DPP derivatives. Here we report a comparative study of three archetypical DPP derivatives, difurylDPP (DFDPP), diphenylDPP (DPDPP), and dithienylDPP (DTDPP), at the interface and in bulk crystals. Using scanning tunneling microscopy (STM) combined with X-ray crystallographic analysis, we demonstrate how the interactions of the (hetero)aromatic substituents interplay with H-bonding, causing dramatic differences in the supramolecular ordering of these structurally similar building blocks. Under all explored conditions, DPDPP exclusively forms H-bonded homoassemblies; DFDPP strongly prefers to co-assemble with alkanoic acids, through a rare lactam···carboxylic acid H-bonded complex, and...

Organic Semiconductors: Carrier‐Selective Traps: A New Approach for Fabricating Circuit Elements with Ambipolar Organic Semiconductors (Adv. Electron. Mater. 3/2017)

In article number 1600537, M. J. Ford et al. show that ambipolar polymer semiconductors can be solution processed with molecular additives to control their charge transport properties. The addititives act as carrier-selective traps, and the researchers show that selecting materials with the appropriate energy level offset can result in either n- or p-type transport from a single ambipolar polymer. Using this discovery, the fabricate efficient complementary inverters with high gain.

Recent progress in quantum chemistry of hetero[8]circulenes

ABSTRACTThis mini-review presents recent advances in theory of electronic and spectral properties of hetero[8]circulenes used as promising fluorescent emitters for organic light-emitting diodes. Special attention is paid to the possibility of their further functionalisation into one-dimensional and two-dimensional (2D) materials. Such materials are predicted to be useful ambipolar organic semiconductors showing high charge carrier mobility. The porous structure of hetero[8]circulene-based nano-arrays can also provide suitable hydrogen storage materials, biomimetic-type nanopores and ionic channels. They serve as a good example of the density functional theory application for design of stable 2D structures, which extends the family of graphene-like materials.

Carrier‐Selective Traps: A New Approach for Fabricating Circuit Elements with Ambipolar Organic Semiconductors

Ambipolar polymer semiconductors and molecular additives (acting as carrier-selective traps) can be solution processed to control ambipolar charge transport capabilities. By selecting materials with appropriate energy level offsets, unipolar n-type or p-type transport can be realized from a single ambipolar polymer. Efficient complementary inverters with high gain are fabricated using this approach.