Search

Three new solution‐processable organic semiconductors (1–3) are synthesized and characterized for p‐type organic field effect transistors (OFETs). The backbone of these small molecules is modified by expanding the central core conjugation from thienothiophene (TT) to dithienothiophene (DTT) and tetrathienoacene (TTA), which are end‐capped with soluble β‐substituted alkyl chains dithienothiophenes (DTTR) to generate DTTR‐TT (1), DTTR‐DTT (2), and DTTR‐TTA (3). The highest mobility of 0.016 cm2 V−1 s−1 is achieved using solution‐sheared DTTR‐TTA film due to the extended conjugated TTA core, which enhances the intermolecular interaction and generates an efficient percolation for the OFET channel. Solution blending of crystalline DTTR‐TT small molecules with oriented‐packing polymer dithienothiophene‐thioalkylbithiophene (PDTT‐SBT) polymer leads to significantly enhanced mobilities from 0.0009 up to 0.22 cm2 V−1 s−1, occurring at an optimized 30% DTTR‐TT composition in the blend. Hole mobility of 30% DTTR‐TT blend is 0.22 cm2 V−1 s−1 which is higher than pristine small molecule DTTR‐TT (0.0009 cm2 V−1 s−1) and polymer PDTT‐SBT (0.067 cm2 V−1 s−1), respectively. An efficient strategy to enhance the mobility of small molecule DTTR‐TT by blending with easily synthesizable PDTT‐SBT polymer is reported. [ABSTRACT FROM AUTHOR]

A series of new metal-free organic dyes based on 3,3′-dithioalkyl-2,2′-bithiophene (SBT) organic chromophores was synthesized for use in dye-sensitized solar cells (DSSCs). Because S(alkyl)⋯S(thiophene) intermolecular interlocking renders the twist angle in the structure as <1°, the SBT core is almost flat, as evidenced by the single crystal, optical, and electrochemical data. Through structural modification of SBT π-linkers with different alkyl chains and conjugated thiophene units, significant chromophore aggregation and interfacial charge recombination can be inhibited. Among all the dyes synthesized, the optimized dye (having a high extinction coefficient of 1.3 × 104 cm−1 M−1 at 497 nm) with the co-adsorbent chenodeoxycholic acid (CDCA) reached a power conversion efficiency (η) of 9.46% under 1 sun (AM 1.5 G, 100 mW cm−2). After 1000 h of testing under 1 sun, a solar cell made with this dye and the co-adsorbent CDCA still maintained 88% of its initial efficiency, compared to 69% for a cell made with N719 dye. Moreover, when tested under a T5 fluorescent lamp of 2400 lux, the η of this dye with CDCA was 12.34%. [ABSTRACT FROM AUTHOR]

Molecular resolution STM is used to study the spatial structure and chirality of adsorbed Δ4,4-dicyclopenta[2,1-b:3,4-b]-dithiophene (TTE) on an Au(111) electrode, revealing an ordered, racemate adlayer made of homogeneously mixed R- and S-TTE on the (1 × 1) substrate and patches of R- or S-only TTE on the reconstructed Au(111) at more and less positive potentials. [ABSTRACT FROM AUTHOR]

Abstract: Four soluble dialkylated tetrathienoacene (TTAR)‐based small molecular semiconductors featuring the combination of a TTAR central core, π‐conjugated spacers comprising bithiophene (bT) or thiophene (T), and with/without cyanoacrylate (CA) end‐capping moieties are synthesized and characterized. The molecule DbT‐TTAR exhibits a promising hole mobility up to 0.36 cm2 V−1 s−1 due to the enhanced crystallinity of the microribbon‐like films. Binary blends of the p‐type DbT‐TTAR and the n‐type dicyanomethylene substituted dithienothiophene‐quinoid (DTTQ‐11) are investigated in terms of film morphology, microstructure, and organic field‐effect transistor (OFET) performance. The data indicate that as the DbT‐TTAR content in the blend film increases, the charge transport characteristics vary from unipolar (electron‐only) to ambipolar and then back to unipolar (hole‐only). With a 1:1 weight ratio of DbT‐TTAR DTTQ‐11 in the blend, well‐defined pathways for both charge carriers are achieved and resulted in ambipolar transport with high hole and electron mobilities of 0.83 and 0.37 cm2 V−1 s−1, respectively. This study provides a viable way for tuning microstructure and charge carrier transport in small molecules and their blends to achieve high‐performance solution‐processable OFETs. [ABSTRACT FROM AUTHOR]

Solution-processed micro-ribbon shaped organic semiconductors and high k hybrid gate dielectric were fabricated for low-voltage-driven organic phototransistors, which integrate the photodetection and memory properties within one single device. [ABSTRACT FROM AUTHOR]

A new series of metal-free alkylated tetrathienoacene (TTAR)-based organic chromophores, TPA–TTAR–TA (R = branched-C8H17, 1, TTAR-b8; R = C15H31, 2, TTAR-15; R = C9H19, 3, TTAR-9), are synthesized for application in dye-sensitized solar cells (DSSCs). Due to the extensively conjugated TTAR π-bridge, all three dyes exhibit high extinction coefficients (1 × 105 M−1 cm−1). By systematically exploring the effects of the TTAR alkyl chain substituents, a significant influence of the dye coverage (orientation) on the TiO2 surfaces is observed. The branched-alkyl TTAR-b8 (1) promotes significant tilting and packing distortion on TiO2 in comparison to more ordered monolayers of linear long alkyls TTAR-15 (2) and TTAR-9 (3). Photophysical measurements on the dye-grafted TiO2 films reveal that the branched-alkylated TTA unit in 1 enhances the electron injection efficiency, in agreement with the high quantum efficiency. Notably, by utilizing a three-dimensional (3D) photonic crystal (PhC) layer to enhance the coherent scattering an increase the light absorption, TTAR-b8 exhibits higher short-circuit current densities and achieved a high PCE of 11.18%. TTAR-b8 is thus the best performing fused-thiophene-based organic DSSC dye reported to date. [ABSTRACT FROM AUTHOR]

A series of dialkylated dithienothiophenoquinoids ( DTTQs), end-functionalized with dicyanomethylene units and substituted with different alkyl chains, are synthesized and characterized. Facile one-pot synthesis of the dialkylated DTT core is achieved, which enables the efficient realization of DTTQs as n-type active semiconductors for solution-processable organic field effect transistors (OFETs). The molecular structure of hexyl substituted DTTQ-6 is determined via single-crystal X-ray diffraction, revealing DTTQ is a very planar core. The DTTQ cores form a 'zig-zag' linking layer and the layers stack in a 'face-to-face' arrangement. The very planar core structure, short core stacking distance (3.30 Å), short intermolecular SN distance (2.84 Å), and very low lying lowest unoccupied molecular orbital energy level of −4.2 eV suggest that DTTQs should be excellent electron transport candidates. The physical and electrochemical properties as well as OFETs performance and thin film morphologies of these new DTTQs are systematically studied. Using a solution-shearing method, DTTQ-11 exhibits n-channel transport with the highest mobility of up to 0.45 cm2 V−1 s−1 and a current ON/OFF ratio ( ION /IOFF) greater than 105. As such, DTTQ-11 has the highest electron mobility of any DTT-based small molecule semiconductors yet discovered combined with excellent ambient stability. Within this family, carrier mobility magnitudes are correlated with the alkyl chain length of the side chain substituents of DTTQs. [ABSTRACT FROM AUTHOR]

Three new organic semiconductors with alkyl chain-substituted tetrathienoacene (TTAR) as the central core and both ends capped with thiophene (DT-TTAR), thienothiophene (DTT-TTAR) and dithienothiophene (DDTT-TTAR) have been synthesized and characterized for organic field effect transistor (OFET) applications. A hole mobility of 0.81 cm2 V−1 s−1 was achieved for the DDTT-TTAR film, which represents the highest mobility yet found for a solution-processable p-type TTAR-based small molecular semiconductors. [ABSTRACT FROM AUTHOR]

Two novel π-conjugated small molecules based on the electron-deficient diketopyrrolopyrrole (DPP) and the electron-rich fused tetrathienoacene (TTA) frameworks are synthesized and characterized. As verified in the bandgap compression of these chromophores by electrochemistry and density functional theory (DFT) computation, these DPP-TAA derivatives exhibit substantial conjugation and ideal MO energetics for light absorption. The large fused TTA core and strong intermolecular S…S interactions enforce excellent molecular planarity, favoring a close-packed thin film morphologies for efficient charge transport, as indicated by grazing incidence wide angle X-ray scattering (GIWAXS), atomic force microscopy (AFM), and transmission electron microscopy (TEM) analysis. Top-gate/bottom-contact thin film transistors based on these systems exhibit hole mobilities approaching 0.1 cm2 V−1 s−1. Organic photovoltaic cells based on DDPP-TTAR:PC71BM blends achieve power conversion efficiencies (PCE) ＞ 4% by systematic morphology tuning and judicious solvent additive selection. [ABSTRACT FROM AUTHOR]

Three new donor-π-donor (D-π-D) tetrathienoacene (thieno[2′,3′:4,5]thieno[3,2- b]thieno[2,3- d]thiophene (TTA))-cored chromophores, end-functionalized with electron-donating triphenylamine (TPA) groups, were developed and characterized for their two-photon-related properties by using both nano- and femtosecond laser pulses as the probing tools. TTA-based chromophores exhibit stronger and more widely dispersed two-photon absorption (2PA) than those of dithienothiophene (DTT)-based congeners. As a consequence, the bithiophene-conjugated TTA chromophore exhibits the highest maximum 2PA cross-section value (up to 2500 GM) with good thermal stability, and thus, it is the best performing two-photon chromophore among the studied model compounds. The bithiophene-conjugated DTT analogue exhibits the second highest maximum two-photon absorptivity of 1950 GM, which is nearly 7 times larger than that of previously reported DTT-based chromophores. [ABSTRACT FROM AUTHOR]

New asymmetric phenyl and perfluorophenyl end-functionalized dithienothiophene (DTT)- and bisdithienothiophene (BDTT)-based fused-thiophene derivatives (FPP-DTT; 1 and FPP-BDTT; 3) were synthesized and characterized for organic thin-film transistor (OTFT) applications. For comparison, symmetric phenyl end-capped dithienothiophene and bisdithienothiophene derivatives DP-DTT (2) and DP-BDTT (4) were also explored in parallel. The crystal structures of all four molecules were determined via single-crystal X-ray diffraction. Asymmetric compounds 1 and 3 exhibit face-to-face π–π stacking, while symmetric 2 and 4 show herringbone stacking. Single-crystal and thin-film transistors based on these four materials were fabricated. For single-crystal transistors, asymmetric FPP-DTT and FPP-BDTT gave high p-channel mobilities of 0.74 and 0.73 cm2 V−1 s−1, respectively, as well as current on/off ratios of ∼105. Symmetric DP-DTT and DP-BDTT gave relatively lower p-channel mobilities of 0.36 and 0.41 cm2 V−1 s−1, respectively. For thin-film transistors, FPP-DTT and DP-DTT films deposited at 25 °C exhibited decent p-channel characteristics with a carrier mobility as high as 0.15 and 0.20 cm2 V−1 s−1, respectively for top-contact/bottom-gate OTFT devices. The device characteristics on various gate dielectrics have been correlated with the film morphologies and microstructures of the corresponding compounds. [ABSTRACT FROM AUTHOR]

Organic photovoltaics (OPVs) and dye-sensitized solar cells (DSSCs) have drawn great interest from both academics and industry, due to the possibility of low-cost conversion of photovoltaic energy at reasonable efficiencies. This review focuses on recent progress in molecular engineering and technological aspects of fused-thiophene-based organic dye molecules for applications in solar cells. Particular attention has been paid to the design principles and stability of these dye molecules, as well as on the effects of various electrolyte systems for DSSCs. Importantly, it has been found that incorporation of a fused-thiophene unit into the sensitizer has several advantages, such as red-shift of the intramolecular charge transfer band, tuning of the frontier molecular energy level, and improvements in both photovoltaic performance and stability. This work also examines the correlation between the physical properties and placement of fused-thiophene in the molecular structure with regard to their performance in OPVs and DSSCs. [ABSTRACT FROM AUTHOR]

New benzothieno[3,2-b]thiophene (BTT) derivatives, end-functionalized with biphenyl (Bp-BTT), naphthalenyl (Np-BTT), and benzothieno[3,2-b]thiophenyl (BBTT; dimer of BTT) moieties, were synthesized and characterized for bottom-gate/top-contact organic thin-film transistors (OTFTs). All three materials exhibit good environmental stability as assessed by thermogravimetric analysis, and no decomposition after extended light exposure, due to their wide band gaps and low-lying HOMOs. The single crystal structures of Bp-BTT and BBTT reveal flat molecular geometries, close π–π stacking, and short sulfur-to-sulfur distances, suggesting an ideal arrangement for charge transport. X-ray diffraction (XRD) measurements verify that the bulk crystal structures are preserved in the polycrystalline thin films. As a consequence, Bp-BTT and BBTT exhibit good OTFT performance, with µ = 0.34 cm2 V−1 s−1 (max) and Ion/Ioff = (3.3 ± 1.6) × 108 for Bp-BTT, and µ = 0.12 cm2 V−1 s−1 (max) and Ion/Ioff = (2.4 ± 0.9) × 107 for BBTT; whereas Np-BTT gives lower device performance with µ = 0.055 cm2 V−1 s−1 (max) and Ion/Ioff = (6.7 ± 3.4) × 108. In addition, octadecyltrichlorosilane (OTS) self-assembled monolayer (SAM) treatment of the SiO2 gate dielectric is found to be effective in enhancing the OTFT performance for all three BTT derivatives, by improving the interfacial semiconductor film morphology and in-plane crystallinity. [ABSTRACT FROM AUTHOR]

Developing efficient interfacial hole transporting materials (HTMs) is crucial for achieving high‐performance Pb‐free Sn‐based halide perovskite solar cells (PSCs). Here, a new series of benzodithiophene (BDT)‐based organic small molecules containing tetra‐ and di‐triphenyl amine donors prepared via a straightforward and scalable synthetic route is reported. The thermal, optical, and electrochemical properties of two BDT‐based molecules are shown to be structurally and energetically suitable to serve as HTMs for Sn‐based PSCs. It is reported here that ethylenediammonium/formamidinium tin iodide solar cells using BDT‐based HTMs deliver a champion power conversion efficiency up to 7.59%, outperforming analogous reference solar cells using traditional and expensive HTMs. Thus, these BDT‐based molecules are promising candidates as HTMs for the fabrication of high‐performance Sn‐based PSCs. [ABSTRACT FROM AUTHOR]

Three new donor-π-donor (D-π-D) tetrathienoacene (thieno[2',3':4,5]thieno[3,2-b]thieno[2,3-d]thiophene (TTA))-cored chromophores, end-functionalized with electron-donating triphenylamine (TPA) groups, were developed and characterized for their two-photon-related properties by using both nano- and femtosecond laser pulses as the probing tools. TTA-based chromophores exhibit stronger and more widely dispersed two-photon absorption (2PA) than those of dithienothiophene (DTT)-based congeners. As a consequence, the bithiophene-conjugated TTA chromophore exhibits the highest maximum 2PA cross-section value (up to 2500 GM) with good thermal stability, and thus, it is the best performing two-photon chromophore among the studied model compounds. The bithiophene-conjugated DTT analogue exhibits the second highest maximum two-photon absorptivity of 1950 GM, which is nearly 7 times larger than that of previously reported DTT-based chromophores., (© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

A new series of metal-free organic chromophores (TPA-TTAR-A (1), TPA-T-TTAR-A (2), TPA-TTAR-T-A (3), and TPA-T-TTAR-T-A (4)) are synthesized for application in dye-sensitized solar cells (DSSC) based on a donor-π-bridge-acceptor (D-π-A) design. Here a simple triphenylamine (TPA) moiety serves as the electron donor, a cyanoacrylic acid as the electron acceptor and anchoring group, and a novel tetrathienoacene (TTA) as the π-bridge unit. Because of the extensively conjugated TTA π-bridge, these dyes exhibit high extinction coefficients (4.5-5.2 × 10(4) M(-1) cm(-1)). By strategically inserting a thiophene spacer on the donor or acceptor side of the molecules, the electronic structures of these TTA-based dyes can be readily tuned. Furthermore, addition of a thiophene spacer has a significant influence on the dye orientation and self-assembly modality on TiO2 surfaces. The insertion of a thiophene between the π-bridge and the cyanoacrylic acid anchoring group in TPA-TTAR-T-A (dye 3) promotes more vertical dye orientation and denser packing on TiO2 (molecular footprint = 79 Å(2)), thus enabling optimal dye loading. Using dye 3, a DSSC power conversion efficiency (PCE) of 10.1% with Voc = 0.833 V, Jsc = 16.5 mA/cm(2), and FF = 70.0% is achieved, among the highest reported to date for metal-free organic DSSC sensitizers using an I(-)/I3(-) redox shuttle. Photophysical measurements on dye-grafted TiO2 films reveal that the additional thiophene unit in dye 3 enhances the electron injection efficiency, in agreement with the high quantum efficiency.