We have investigated the influence of the symmetry of the side chain substituents in high-mobility, solution processable n-type molecular semiconductors on the performance of organic field-effect transistors (OFETs). We compare two molecules with the same conjugated core, but either symmetric or asymmetric side chain substituents, and investigate the transport properties and thin film growth mode using scanning Kelvin probe microscopy (SKPM) and atomic force microscopy (AFM). We find that asymmetric side chains can induce a favorable two-dimensional growth mode with a bilayer structure, which enables ultrathin films with a single bilayer to exhibit excellent transport properties, while the symmetric molecules adopt an unfavorable three-dimensional growth mode in which transport in the first monolayer at the interface is severely hindered by high-resistance grain boundaries. © 2014 American Chemical Society.

Yuanyuan Hu    Berdunov    Chongan Di    Nandhakumar Iris S.    Fengjiao Zhang    高希珂    朱道本     Henning Sirringhaus   

ACS Nano

2014

Naphthalenediimides (NDI) fused with two 2-(1,3-dithiol-2-ylidene)acetonitrile moieties (NDI-DTYA2), a novel strong electron-deficient monomer, was designed and readily synthesized by aromatic nucleophilic substitution to develop n-type polymers. Two NDI-DTYA2 based donor-acceptor (D-A) polymers P(NDI-DTYA2-1T) and P(NDI-DTYA2-2T) have been prepared (1T = thiophene, 2T = 2,2′-bithiophene) and showed low-lying LUMO energies (<-4.2 eV) and near-infrared optical absorptions (optical band gap <1.3 eV). Although the film feature of these polymers is amorphous, pure electron transport with high mobility of up to 0.38 cm V s could be achieved for their bottom gate organic thin film transistors, which was among the highest performances for unipolar n-type polymers. The results demonstrate that NDI-DTYA2 derivatives are promising building blocks for developing electron transport π-functional materials.

Zheng Zhao    Fengjiao Zhang    Yunbin Hu    Wang Zhongli    Leng Bing    高希珂    Chongan Di    朱道本    

ACS Macro Letters

2014

Dicyanomethylene-substituted quinoidal dithieno[2,3-d;2′,3′-d′]benzo[1,2-b;4,5-b′] dithiophene compounds (QDTBDTs) with alkyl chains branched at different positions were synthesized. Thin-film transistor characteristics showed that the type of charge carriers in QDTBDTs could be tuned by changing the branching position of the alkyl chains. QDTBDT-2C exhibited n-channel behavior, and the observed electron mobility was 0.57 cm² V^-1 s^-1 without post-treatment, one of the highest values reported for spin-coated thin-film transistors with no annealing under ambient conditions. QDTBDT-4C-based transistors displayed electron-dominated ambipolar transport behavior, with electron mobilities reaching 0.2 cm² V^-1 s^-1 and hole mobilities in the range of 10^-3-10^-4 cm² V^-1 s^-1. QDTBDT-3C showed solution-concentration-dependent carrier transport characteristics, exhibiting n-type behavior at low solution concentrations and ambipolar performance at high solution concentrations with an electron mobility of 0.22 cm² V^-1 s^-1 and a hole mobility of 0.034 cm² V^-1 s^-1. CMOS-like inverters fabricated from QDTBDT-2C displayed high gain and high noise margins. (Chemical Equation Presented).

Jie Li    乔小兰    Xiong Yu    李洪祥    朱道本    

Chemistry of Materials

2014

The synthesis, crystal structure, Raman spectra, conductivity, and magnetism of the title charge-transfer salt (1) composed of BEDT-TTF [bis(ethylenedithio)tetrathiafulvalene], one-dimensional [Fe(C2O4)Cl2^-]n, and the solvent CH2Cl2, are described and interpreted. Electrochemical oxidation of neutral BEDT-TTF in the presence of [(C2H5)3NH][Fe(C2O4)Cl2] in a CH2Cl2/CH3OH solution yields crystals of 1, which crystallizes in triclinic form. In 1, two donor molecules stack in a face-to-face manner as a BEDT-TTF dimer. The BEDT-TTF dimers form a (4,4) grid in the ab plane. The cavity of the (4,4) grid is occupied by two CH2Cl2 molecules. The donor layers are separated by sheets of [Fe(C2O4)Cl2^-]n anions with a zigzag chain along the a axis. There are S⋯S interactions between the donors, and S⋯Cl interactions between the donor and the anion. On the χ vs. T plot, a broad maximum is observed around 45 K, showing the existence of antiferromagnetic interactions between the metal atoms in the low-dimensional system. The formal charge of the donor molecules is assigned 1.0+ based on the bond lengths of the TTF core and on the Raman spectra. The material is a semiconductor with σrt = 1.8 × 10^-5 S/cm. The title compound has been synthesized and studied, and it was found that the donor layers in the organic-inorganic hybrid charge-transfer salt, which is composed of BEDT-TTF^1.0+ dimers and CH2Cl2, are separated by zigzaged anion chains. The compound is a semiconductor and shows strong antiferromagnetic interactions between the oxalate-bridged metal atoms.

Zhang Bin    Yan Zhang    Zengqiang Gao    Chang Guang-Cai    Su ShaoKui    Wang Dongwei    Yanjun Guo    朱道本    

European Journal of Inorganic Chemistry

2014

Poly[Cu(Cu-ethylenetetrathiolate)] was synthesized, and its thermoelectric (TE) properties were optimized using chemical oxidation and reduction. Both X-ray absorption fine structure and X-ray photoelectron spectroscopy techniques were used to characterize the polymers. The best TE properties were achieved with a PF of 26.0 μW m K and a ZT of 0.019 at 360 K. © 2013 Elsevier B.V.

Sheng Peng    Yimeng Sun    Fei Jiao    Caiming Liu    Wei Xu    朱道本    

Synthetic Metals

2014

Modification of the electronic structures of two benchmark donor-acceptor (D-A) copolymers poly[(4,4′-bis(2-ethylhexyl)dithieno[3,2-b:2′, 3′-d]silole)-2,6-diyl-alt-(2,1,3-benzothiadiazole)-4,7-diyl] (PSBTBT) and poly[{2,5-bis(2-hexyldecyl)-2,3,5,6-tetrahydro-3,6-dioxopyrrolo[3,4-c]pyrrole-1, 4-diyl}-alt-{[2,2′:5′,2″-terthiophene]-5,5″-diyl}] (PDPP3T) by chemical doping is reported. Simply by dipping polymer films into dopant solution, high electrical conductivity is achieved and thermoelectric property of the films is optimized. Despite their deep HOMO levels, optical absorption extending continuously to 2000 nm is observed in PSBTBT, and a high power factor around 25 μW m K is obtained in PDPP3T. Furthermore, temperature-dependent measurement of electrical conductivity and Seebeck coefficients is carried out to understand transport mechanisms and energetic distribution of carrier density of states (DOS). In parallel, doping treatment and corresponding characterizations are performed on donor polymers poly(3-hexylthiophene) (P3HT) and poly(2,5-bis(3-dodecylthiophen- 2-yl)thieno[3,2-b]thiophene) (PBTTT-C12) for comparison. Ultimately, based on comprehensive characterizations and comparisons of the four polymers in terms of bulk mobility, DOS, film microstructures, and molecular structures, etc., a primitive correlation between solution-processable polymeric semiconductors and thermoelectric properties of their doped products is established. © 2014 American Chemical Society.

Qian Zhang    Yimeng Sun    Wei Xu    朱道本    

Macromolecules

2014

Novel conjugated macrocycles, thiophene-substituting tetrathia[22] annulenes[2,1,2,1] (TTAs, and 5b), were synthesized through a convenient four-step procedure. They were evidenced to have high aromaticity by NMR, UV-vis absorption spectra, and calculation. Their UV-vis absorption spectra, thermal stability, electrochemical properties, thin film morphology were studied and the field-effect transistors based on 5a and 5b through a vapor deposition method performed good with reproducible bulk-like carrier mobilities (as high as 0.53 cm V S) and high on/off ratios (as high as 9.0×10), which was among the best records in this series. © 2014 Elsevier Ltd. All rights reserved.

Liu Hang    Qin Yunke    Dazhen Huang    Wei Xu    朱道本    

Tetrahedron

2014

A π-extended tetrathiafulvalene (exTTF) containing a conjugated pentacene moiety showed a large binding affinity toward C in solution. The crystal structure analysis of the cocrystal formed by this exTTF and C revealed that strong π-π interactions existed between C and naphthalene and 1,3-dithiol-2-ylidene units. This journal is © the Partner Organisations 2014.

Zhou Zhongmin    Qin Yunke    Wei Xu    朱道本    

Chemical Communications

2014

The novel aromatic heteromacrocycle, p-bromophenyl substituted tetrathia[22]annulene[2,1,2,1] was synthesized as a convenient derivable building block to obtain a variety of tetrathia[22]annulene[2,1,2,1] derivatives, which were recently found to be promising p-type semiconducting materials for OFETs with some unique properties. Furthermore the annulene itself was found to perform well as an active material in OFETs. A thin film transistor based on the annulene had the best hole mobility of 0.73 cm Vs and the on/off ratio of 1.4 × 10, which are class leading amongst the macrocyclic field-effect materials. © 2014 Elsevier Ltd. All rights reserved.

Liu Hang    Qin Yunke    Dazhen Huang    Wei Xu    朱道本    

Dyes and Pigments

2014

A kind of bulk organic thermoelectric material namely Cu(I)- ethylenetetrathiolate was synthesized, and its thermoelectric properties were optimized using chemical oxidation and reduction. Both X-ray absorption fine structure and X-ray photoelectron spectroscopy techniques were used to characterize the complex. The material showed p-type property and the best thermoelectric properties were achieved with a power factor of 118.2 μW m K and a ZT of 0.060 at 400 K. A thermogenerator based on this material and n-type poly[K(Ni-ethylenetetrathiolate)] had an open voltage of 1.51 V and a short current of 2.71 mA under a temperature difference of 60 K. The maximum power output exceeded 1 mW, which is the best performance of the thermoelectric modules based on organic thermoelectric materials. The thermogenerator could power a liquid crystal display calculator, which shed light on the practical use of organic thermoelectric materials. © 2014 Elsevier B.V.

Sheng Peng    Yimeng Sun    Fei Jiao    Chongan Di    Wei Xu    朱道本    

Synthetic Metals

2014