High-performance Organic Semiconductors Research Articles

Targeted deposition of organic semiconductor stripes onto rigid, flexible, and three-dimensional substrates

Wetting-mediated two-phase dip coating enables deposition of high-performance organic semiconductor stripes at pre-specified locations on rigid, flexible, and three-dimensional substrates.

Understanding the grain-growth mechanism of high-performance organic semiconducting diphenyl-dibenzothiopheno[6,5-b:6′,5′-f]thieno[3,2-b]thiophene molecules

We report here our investigation on the grain-growth mechanism of diphenyl-dibenzothiopheno[6,5-b:6′,5′-f]thieno[3,2-b]thiophene (DPh-DBTTT), which was recently published as a high-performance organic semiconductor. Atomic force microscopy revealed that unconventional needle-like structures grew on the surface of DPh-DBTTT thin films, and these structures became more dominant as the film thickness increased and the deposited film's surface temperature decreased. In combination with the crystal structure simulations, the grazing-incidence wide-angle x-ray scattering data indicated that the DPh-DBTTT molecules preferred an edge-on orientation near the interface between the substrate and DPh-DBTTT thin film, while the needle-like structures consisted of a face-on arrangement of the molecules. We suggest that this structural change originates from the large step-edge energy barrier of the DPh-DBTTT molecules. Our findings would be highly valuable to the design of new high-performance organic semiconducting materials and optimization of the conditions of thin-film deposition.

4,5,9,10-Pyrene Diimides: A Family of Aromatic Diimides Exhibiting High Electron Mobility and Two-Photon Excited Emission.

The design and synthesis of high-performance n-type organic semiconductors are important for the development of future organic optoelectronics. Facile synthetic routes to reach the K-region of pyrene and produce 4,5,9,10-pyrene diimide (PyDI) derivatives are reported. The PyDI derivatives exhibited efficient electron transport properties, with the highest electron mobility of up to 3.08 cm2 V-1 s-1 . The tert-butyl-substituted compounds (t-PyDI) also showed good one- and two-photon excited fluorescence properties. The PyDI derivatives are a new family of aromatic diimides that may exhibit both high electron mobility and good light-emitting properties, thus making them excellent candidates for future optoelectronics.

An Ultrasensitive Organic Semiconductor NO2 Sensor Based on Crystalline TIPS‐Pentacene Films

Organic semiconductor gas sensor is one of the promising candidates of room temperature operated gas sensors with high selectivity. However, for a long time the performance of organic semiconductor sensors, especially for the detection of oxidizing gases, is far behind that of the traditional metal oxide gas sensors. Although intensive attempts have been made to address the problem, the performance and the understanding of the sensing mechanism are still far from sufficient. Herein, an ultrasensitive organic semiconductor NO2 sensor based on 6,13-bis(triisopropylsilylethynyl)-pentacene (TIPS-petacene) is reported. The device achieves a sensitivity over 1000%/ppm and fast response/recovery, together with a low limit of detection (LOD) of 20 ppb, all of which reach the level of metal oxide sensors. After a comprehensive analysis on the morphology and electrical properties of the organic films, it is revealed that the ultrahigh performance is largely related to the film charge transport ability, which was less concerned in the studies previously. And the combination of efficient charge transport and low original charge carrier concentration is demonstrated to be an effective access to obtain high performance organic semiconductor gas sensors.

Solution-processed organic–inorganic hybrid CMOS inverter exhibiting a high gain reaching 890

In this letter, we present a fabrication scheme and device performances of an organic–inorganic hybrid CMOS inverter employing a high-performance p-type organic semiconductor and an amorphous metal oxide layers. A deterioration of the oxide layer during device processing, which is often found in solution-processed semiconductor oxides, can be avoided by a one-shot solution-crystallization technique utilizing a polymer-blend. Both the p- and the n-type channels exhibited excellent transistor performances with high carrier mobilities and with precipitous turn-on behaviors near the gate voltages of 0 V, resulting in a successful demonstration of an ideal CMOS inverter operation with gain of 890. This result will update a potential excellence of organic–inorganic hybrid CMOS circuits in practical devices.

Critical Role of Molecular Symmetry for Charge Transport Properties: A Paradigm Learned from Quinoidal Bithieno[3,4-b]thiophenes

High molecular symmetry is always observed in high-performance organic semiconductors. However, whether it is an essential factor for molecular design is unclear. In this work, we designed and synthesized three quinoidal isomers, QBTT-o, QBTT-i, and QBTT-s, with different sulfur orientations and a stable E configuration to investigate the relationship between the structure symmetry and organic thin-film transistor performance. We found that QBTT-o and QBTT-i with high C2h symmetry exhibit electron mobilities of 0.02 and 0.15 cm2 V–1 s–1, respectively, while QBTT-s exhibits an unexpectedly high electron mobility of 0.32 cm2 V–1 s–1 with Ion/Ioff ratios of ≤106. The enhanced electron mobilities from QBTT-o and QBTT-i to QBTT-s can be attributed to the different sulfur orientations, especially, molecular symmetry. The thin-film microstructures of three QBTTs were systematically investigated by grazing incidence wide-angle X-ray scattering, near-edge X-ray absorption fine structure spectroscopy, atomic force ...

Theoretical study of pyrene derivatives as high performance organic semiconductor materials

The pyrene systems are remarkable candidates for organic semiconductor materials. The theoretical investigation on electronic and transport properties of a series of pyrene derivatives has been carried out by quantum mechanics (QM) calculations combined with Marcus-Hush electron transfer theory and density functional theory (DFT). Various structure modifications of 12 different pypene derivative molecules are investigated to reveal structure-mobility relationships of the organic materials, such as introducing different substitution groups in different positions, changing the central core of the molecule by linking different backbone structure. The theoretical calculation results are in good agreement with the experimental results, such as the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) energies. The reorganization energies and charge mobility are estimated based on molecule single-crystal structures and incoherent charge-hopping transfer model at 300K. For designing high performance organic materials, the hole mobility is predicted to reach a high value of 2.95cm2V−1s−1 for compound 2,7-diphenyl-substituted derivative and the largest electron mobility for 4,5-dithienypyrene as 6.24cm2V−1s−1, indicating that pyrene derivatives are promising candidates for organic semiconductors. The 3D simulation mobility figures are calculated step by step. In this study, the charge transport properties largely depend upon the packing mode of organic semiconducting molecules and the structural change of the substituent group. Our calculation results could provide enlightening information on possible methods to increase the charge mobility and the design for organic electronic devices with high-mobility.

Pursuing High-Mobility n-Type Organic Semiconductors by Combination of "Molecule-Framework" and "Side-Chain" Engineering.

"Molecule-framework" and "side-chain" engineering is powerful for the design of high-performance organic semiconductors. Based on 2DQTTs, the relationship between molecular structure, film microstructure, and charge-transport property in organic thin-film transistors (OTFTs) is studied. 2DQTT-o-B exhibits outstanding electron mobilities of 5.2 cm2 V-1 s-1 , which is a record for air-stable solution-processable n-channel small-molecule OTFTs to date.

Determination of crystal orientation in organic thin films using optical microscopy

The electrical behavior of devices based on highly crystalline thin films of organic semiconductors is inherently anisotropic. Thin film optimization requires simple and accessible means to characterize the orientation of the constituent crystals. The standard polarized light microscopy (PLM) provides a contrast between different crystallites but fails to distinguish crystals with relative orientation of 90°. In this paper, we discuss two methods that enable the unambiguous identification of crystal orientation in thin films of optically anisotropic materials: PLM with a full-wave retardation plate and differential interference contrast (DIC). The latter is standard on most microscopes and delivers images with high contrast and good color balance.As an illustration, we use DIC to extract the optical properties of highly crystalline thin films of three high-performance organic semiconductors: rubrene, 6,13-bis(triisopropylsilylethynyl)pentacene (TIPS-pentacene) and 2,7-dioctyl[1]benzothieno[3,2-b][1]benzothiophene (C8-BTBT). Building on the relation between optical properties and crystal orientation, we demonstrate how DIC characterizes the in-plane crystal orientation of these thin films. This leads to the identification of the fast growth direction of the crystal front.

Molecular Requirements for Printable Organic Semiconductors in 7-Alky1-2-phenyl[1]benzothieno[3,2-b][1]benzothiophenes (Ph-BTBT-Cn’s)

Here we discuss requirements for high performance and solution processable organic semiconductors, by presenting a systematic investigation of 7-alkyl-2-phenyl[1]benzothieno[3,2-b][1]benzothiophenes (Ph-BTBT-C n ’s). We found that the solubility and thermal properties of Ph-BTBT-C n ’s depend systematically on the substituted alkyl-chain length n. The observed features are well understood in terms of the change of molecular packing motif with n: The compounds with n ≤ 4 do not form independent alkyl chain layers, whereas those with n ≥ 5 form isolated alkyl chain layers. The latter compounds afford a series of isomorphous bilayer-type crystal structures that form two-dimensional carrier transport layers within the crystals. We also show that the Ph-BTBT-C10 afford high performance single-crystalline field-effect transistors the mobility of which reaches as high as 15.9 cm2/Vs. These results demonstrate a crucial role of the substituted alkyl chain length for obtaining high performance organic semiconductors and field-effect transistors.

A Furan-Thiophene-Based Quinoidal Compound: A New Class of Solution-Processable High-Performance n-Type Organic Semiconductor.

The furan-thiophene-based quinoidal organic semiconductor, TFT-CN, is designed and synthesized. TFT-CN displays a high electron mobility of 7.7 cm(2) V(-1) s(-1) , two orders of magnitude higher than the corresponding thiophene-based derivative.

Perfluoroalkylation of Square-Planar Transition Metal Complexes: A Strategy To Assemble Them into Solid State Materials with a π–π Stacked Lamellar Structure

Formation of π–π stacked lamellar structure is important for high performance organic semiconductor materials. We previously demonstrated that perfluoroalkylation of aromatics and heteroaromatics was one of the strategies to design organic crystalline materials with π–π stacked lamellar structures while improving air stability as a result of the strong electron withdrawing ability of perfluoroalkyl substituents. Square-planar transition metal complexes with large π-conjugated ligands are also an important category of semiconductor materials. We have perfluoroalkylated square-planar transition metal complexes, leading to the formation of a π–π stacked lamellar crystal packing motif in the solid state. Here we report six crystal structures of Pd and Pt complexes with bis-perfluorobutylated catechol ligand as one of the two ligands that bonds to the metal centers. This structural design possesses similar molecular topology when compared to perfluoroalkylated aromatics and heteroaromatics we have reported pre...

Soluble acetylenic molecular glasses based on dithienyldiketopyrrolopyrrole for organic solar cells

We present the synthesis and photovoltaic response of soluble glass-forming molecules containing a dithienyldiketopyrrolopyrrole core and difluorenylarylamine endgroups, linked through an acetylene bond. Introducing the 2,6-naphthylene moiety vs. 1,4-phenylene leads to an increased glass transition temperature (Tg) and hole mobility. Thus, Tg = 107.7 °C, μh = 7.95 × 10−5 cm2 V−1 s−1 for the 1,4- phenylene compound, while Tg = 119.4 °C, μh = 9.17 × 10−5 cm2 V−1 s−1 for the 2,6-naphthylene compound. Thermal annealing the as-cast films of both compounds below Tg resulted in little change in optical absorption. The preliminary characterization of the bulk hetero-junction solar cells showed that the 2,6-naphthylene compound generally provides a higher power conversion efficiency than the 1,4-phenylene compound, due probably to its enhanced hole transport. The photoluminescence experiments show a weak exciplex emission around 880 nm for the blends containing the new dyes and PC61BM. The present work may be useful for further efforts toward high-performance cost-effective acetylenic organic semiconductors for organic solar cells with thermally stable morphology.

Theoretical design of benzo[1,2-b:3,4-b′:5,6-b′′]tristhianaphthene and its derivatives as high performance organic semiconductors

In order to probe the effects of substituents (F and CN) attached to benzo[1,2-b:3,4-[Formula: see text]:5,6-[Formula: see text]]tristhianaphthene (BTTP) on their charge carrier transport properties, we investigated the characteristics of molecular structures and charge transport properties of BTTP and its derivatives (BTTP1, BTTP2, BTTP3, BTTP4, and BTTP5). Six crystal structures were predicted by the Monte Carlo-simulated annealing method with the embedded electrostatic potential charges method. Even a subtle change of geometrical structures may result in a great change of the reorganization energy. With increasing numbers of substituted fluorine atoms, the reorganization energy of the BTTP derivative increases, which is disadvantageous to the electron transport. In contrast, the attachment of the electron-withdrawing cyano groups to BTTP decreases the reorganization energy and raises the electron affinity, which is beneficial to electron injection and charge carrier stabilization. The introduction of cyano groups also results in an enhancement of [Formula: see text]–[Formula: see text] interaction and leads to an increase in the transfer integrals. Among the six compounds, the novel compound BTTP4 has the largest electron mobility (1.154[Formula: see text]cm[Formula: see text]) on account of its larger transfer integral and smaller reorganization energy, indicating that BTTP4 is a promising high-performance n-type organic semiconductor and worth to synthesize. The analysis of angular-resolution anisotropic mobilities for the BTTP and BTTP4 shows that it is helpful to control the orientations of the conducting channels for a better charge transport efficiency. This work provides a rational strategy for the design of high-performance n-type organic semiconductors from molecule to crystal structure.

Low-resistance contacts of electroless-plated metals with high-mobility organic semiconductors: Novel organic field-effect transistors with solution-processed electrodes

The establishment of a reliable vacuum-free method for the formation of electrical contacts on high-performance organic semiconductors has become an urgent task due to rapid progress made in the development of solution-processable high-mobility organic field-effect transistors (OFETs). We have recently proposed that electroless plating, a standard technology to mass produce wirings in currently commercialized electronic devices, is suited for high-performance solution-crystallized OFETs. A low contact resistance at the source and drain electrodes is necessary with organic semiconductors for high-speed device operation; therefore, we have evaluated the contact resistance using the transfer line method. A top-contact geometry with sufficient contact area is employed to achieve stable carrier injection, which has enabled contact resistances as low as 1.4 kΩ cm on a polyethylene naphthalate substrate at a gate voltage of −10 V. This marks outstanding performance among the solution-processed metal electrodes reported for OFETs, particularly on plastic substrates. The result indicates that high-quality boundaries with minimized trap densities are realized due to the mild conditions of the electroless plating process at room temperature.

TD-DFT study on electron transfer mobility and intramolecular hydrogen bond of substituted indigo derivatives

The density functional theory (DFT) and time-dependent density functional theory (TDDFT) method were carried out to investigate the ground and excited states of indigo and its derivative molecules. The results demonstrate that the intramolecular hydrogen bond I is weakened and the intramolecular hydrogen bond II is strengthened upon photo-excitation to the S1 state. In the absorption spectra, the substitution at R4R4, of indigo causes a significant redshift. In addition, the halogen substitution obviously increases the electron transfer mobility of indigo. It is proved that the halogen substitution may be a new method to design high performance organic semiconductors.

Monolayer-Mediated Growth of Organic Semiconductor Films with Improved Device Performance.

Increased interest in wearable and smart electronics is driving numerous research works on organic electronics. The control of film growth and patterning is of great importance when targeting high-performance organic semiconductor devices. In this Feature Article, we summarize our recent work focusing on the growth, crystallization, and device operation of organic semiconductors intermediated by ultrathin organic films (in most cases, only a monolayer). The site-selective growth, modified crystallization and morphology, and improved device performance of organic semiconductor films are demonstrated with the help of the inducing layers, including patterned and uniform Langmuir-Blodgett monolayers, crystalline ultrathin organic films, and self-assembled polymer brush films. The introduction of the inducing layers could dramatically change the diffusion of the organic semiconductors on the surface and the interactions between the active layer with the inducing layer, leading to improved aggregation/crystallization behavior and device performance.

Rational design of bio-inspired high-performance ambipolar organic semiconductor materials based on indigo and its derivatives

Indigoids have received much attention as the candidates of sustainable ambipolar organic semiconductor. However, the low charge carrier mobilities extremely limit their practical applications. Therefore, in-depth understanding of their electronic-structure properties and rational molecular modifications are urgently required. Here, we propose a promising strategy to design ambipolar organic semiconductors based on indigo fragments. Moreover, we predicted the organic crystal structures by evolutionary algorithm combined with DFT-D method. Charge transport properties have been significantly improved for the designed molecules, such as narrower energy gaps, higher electron affinity, larger transfer integrals as well as much smaller reorganization energies for hole and electron. Thusly, remarkable ambipolar charge transport behavior has been predicted, for example, the charge carrier mobilities are up to μh/μe=7.71/5.42cm2V−1s−1 for NN-indigo-6,6′-2CN and μh/μe=5.15/2.13cm2V−1s−1 for C9-NN-indigo-6,6′-2CN respectively.

Bulky end-capped [1]benzothieno[3,2-b]benzothiophenes: reaching high-mobility organic semiconductors by fine tuning of the crystalline solid-state order.

A series of bulky end-capped [1]benzothieno[3,2-b]benzothiophenes (BTBTs) are developed in order to tune the packing structure via terminal substitution. A coupled theoretical and experimental study allows us to identify 2,7-di-tert-butylBTBT as a new high-performance organic semiconductor with large and well-balanced transfer integrals, as evidenced by quantum-chemical calculations. Single-crystal field-effect transistors show a remarkable average saturation mobility of 7.1 cm(2) V(-1) s(-1) .

ChemInform Abstract: Use of the Wilkinson Catalyst for the ortho‐C—H Heteroarylation of Aromatic Amines: Facile Access to Highly Extended π‐Conjugated Heteroacenes for Organic Semiconductors.

AbstractThe heteroarylation products can be further converted to give heteroacenes, e.