Imperial College London

ProfessorMartinHeeney

Faculty of Natural SciencesDepartment of Chemistry

Professor of Organic Materials
 
 
 
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Contact

 

+44 (0)20 7594 1248m.heeney Website

 
 
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Location

 

401GMolecular Sciences Research HubWhite City Campus

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Summary

 

Publications

Publication Type
Year
to

315 results found

Isakov I, Paterson AF, Solomeshch O, Tessler N, Zhang Q, Li J, Zhang X, Fei Z, Heeney M, Anthopoulos TDet al., 2016, Hybrid complementary circuits based on p-channel organic and n-channel metal oxide transistors with balanced carrier mobilities of up to 10 cm(2)/Vs, Applied Physics Letters, Vol: 109, ISSN: 1077-3118

We report the development of hybrid complementary inverters based on p-channel organic andn-channel metal oxide thin-film transistors (TFTs) both processed from solution at <200 C. For theorganic TFTs, a ternary blend consisting of the small-molecule 2,7-dioctyl[1]benzothieno[3,2-b][1]benzothiophene, the polymer indacenodithiophene-benzothiadiazole (C16IDT-BT) and the p-typedopant C60F48 was employed, whereas the isotype In2O3/ZnO heterojunction was used for the nchannelTFTs. When integrated on the same substrate, p- and n-channel devices exhibited balancedcarrier mobilities up to 10 cm2/Vs. Hybrid complementary inverters based on these devices show highsignal gain (>30 V/V) and wide noise margins (70%). The moderate processing temperaturesemployed and the achieved level of device performance highlight the tremendous potential of the technologyfor application in the emerging sector of large-area microelectronics.

Journal article

Boufflet P, Casey A, Xia Y, Stavrinou PN, Heeney Met al., 2016, Pentafluorobenzene end-group as a versatile handle for para fluoro "click" functionalization of polythiophenes, Chemical Science, Vol: 8, Pages: 2215-2225, ISSN: 2041-6520

A convenient method of introducing pentafluorobenzene (PFB) as a single end-group in polythiophene derivatives is reported via in situ quenching of the polymerization. We demonstrate that the PFB-group is a particularly useful end-group due to its ability to undergo fast nucleophilic aromatic substitutions. Using this molecular handle, we are able to quantitatively tether a variety of common nucleophiles to the polythiophene backbone. The mild conditions required for the reaction allows sensitive functional moieties, such as biotin or a cross-linkable trimethoxysilane, to be introduced as end-groups. The high yield enabled the formation of a diblock rod-coil polymer from equimolar reactants under transition metal-free conditions at room temperature. We further demonstrate that water soluble polythiophenes end-capped with PFB can be prepared via the hydrolysis of an ester precursor, and that such polymers are amenable to functionalization under aqueous conditions.

Journal article

Casey A, Han Y, Gann E, Green JP, McNeill CR, Anthopoulos TD, Heeney Met al., 2016, Vinylene-linked oligothiophene–difluorobenzothiadiazole copolymer for transistor applications, ACS Applied Materials & Interfaces, Vol: 8, Pages: 31154-31165, ISSN: 1944-8244

The synthesis of the novel donor-acceptor monomer 4,7-bis[(E)-2-(5-bromo-3-dodecylylthiophen-2-yl)ethenyl]-5,6-difluoro-2,1,3-benzothiadiazole (FBT-V2T2) is reported. Polymerization with 4,4'-ditetradecyl-5,5'-bistrimethylstannyl-2,2'-bithiophene afforded a highly crystalline polymer that aggregated strongly in solution. Polymer films were well ordered resulting in high performance field-effect transistors with low onset voltages, negligible hysteresis, high channel current on/off ratios and peak hole mobilities of up to 0.5 cm2V-1s-1. Notably the transistors exhibited close to ideal behavior with extracted mobilities almost independent of gate of voltage.

Journal article

Boufflet P, Wood S, Wade J, Fei Z, Kim JS, Heeney Met al., 2016, Comparing blends and blocks: Synthesis of partially fluorinated diblock polythiophene copolymers to investigate the thermal stability of optical and morphological properties, Beilstein Journal of Organic Chemistry, Vol: 12, Pages: 2150-2163, ISSN: 1860-5397

The microstructure of the active blend layer has been shown to be a critically important factor in the performance of organic solar devices. Block copolymers provide a potentially interesting avenue for controlling this active layer microstructure in solar cell blends. Here we explore the impact of backbone fluorination in block copolymers of poly(3-octyl-4-fluorothiophene)s and poly(3-octylthiophene) (F-P3OT-b-P3OT). Two block co-polymers with varying block lengths were prepared via sequential monomer addition under Kumada catalyst transfer polymerisation (KCTP) conditions. We compare the behavior of the block copolymer to that of the corresponding homopolymer blends. In both types of system, we find the fluorinated segments tend to dominate the UV–visible absorption and molecular vibrational spectral features, as well as the thermal behavior. In the block copolymer case, non-fluorinated segments appear to slightly frustrate the aggregation of the more fluorinated block. However, in situ temperature dependent Raman spectroscopy shows that the intramolecular order is more thermally stable in the block copolymer than in the corresponding blend, suggesting that such materials may be interesting for enhanced thermal stability of organic photovoltaic active layers based on similar systems.

Journal article

Han Y, Barnes G, Lin Y-H, Martin J, Al-Hashimi M, AlQaradawi SY, Anthopoulos TD, Heeney Met al., 2016, Doping of large ionization potential indenopyrazine polymers via Lewis acid complexation with tris(pentafluorophenyl)borane: a simple method for improving the performance of organic thin-film transistors, Chemistry of Materials, Vol: 28, Pages: 8016-8024, ISSN: 1520-5002

Molecular doping, under certain circumstances, can be used to improve the charge transport in organic semiconductors through the introduction of excess charge carriers which can in turn negate unwanted trap states often present in organic semiconductors. Here, two Lewis basic indenopyrazine copolymers with large ionization potential (5.78 and 5.82 eV) are prepared to investigate the p-doping efficiency with the Lewis acid dopant, tris(pentafluorophenyl)borane, using organic thin-film transistors (OTFTs). The formation of Lewis acid–base complex between the polymer and dopant molecules is confirmed via optical spectroscopy and electrical field-effect measurements, with the latter revealing a dopant-concentration-dependent device performance. By adjusting the amount of p-dopant, the hole mobility can be increased up to 11-fold while the OTFTs’ threshold voltages are reduced. The work demonstrates an alternative doping mechanism other than the traditional charge transfer model, where the energy level matching principle can limit the option of dopants.

Journal article

Fei Z, Han Y, Martin J, Scholes FH, Al-Hashimi M, AlQaradawi SY, Stingelin N, Anthopoulos TD, Heeney Met al., 2016, Conjugated Copolymers of Vinylene Flanked Naphthalene Diimide, Macromolecules, Vol: 49, Pages: 6384-6393, ISSN: 0024-9297

We report the synthesis of a novel naphthalene diimide (NDI) monomer containing two (tributylstannyl)vinyl groups. The utility of this building block is demonstrated by its copolymerization with five different electron-rich comonomers under Stille conditions. The resulting high molecular weight polymers show red-shifted optical absorptions in comparison to the analogous polymers without the vinylene spacer and a significant increase in the intensity of the low-energy intramolecular charge transfer band. The polymers all exhibit ambipolar behavior in bottom-gate, top-contact organic thin-film transistors. The insertion of a solution-processed barium hydroxide layer between the polymer and the gold electrode led to unipolar behavior with improved electron mobilities.

Journal article

Paterson AF, Treat ND, Zhang W, Fei Z, Wyatt-Moon G, Faber H, Vourlias G, Patsalas PA, Solomeshch O, Tessler N, Heeney M, Anthopoulos TDet al., 2016, Small Molecule/Polymer Blend Organic Transistors with Hole Mobility Exceeding 13 cm V−1 s−1, Advanced Materials, Vol: 28, Pages: 7791-7798, ISSN: 1521-4095

A ternary organic semiconducting blend composed of a small-molecule, a conjugated polymer, and a molecular p-dopant is developed and used in solution-processed organic transistors with hole mobility exceeding 13 cm(2) V(-1) s(-1) (see the Figure). It is shown that key to this development is the incorporation of the p-dopant and the formation of a vertically phase-separated film microstructure.

Journal article

Casey A, Dimitrov SD, Shakya-Tuladhar P, Fei Z, Nguyen M, Han Y, Anthopoulos TD, Durrant JR, Heeney Met al., 2016, Effect of Systematically Tuning Conjugated Donor Polymer Lowest Unoccupied Molecular Orbital Levels via Cyano Substitution on Organic Photovoltaic Device Performance, Chemistry of Materials, Vol: 28, Pages: 5110-5120, ISSN: 0897-4756

We report a systematic study into the effects of cyano substitution on the electron accepting ability of the common acceptor 4,7-bis(thiophen-2-yl)-2,1,3-benzothiadiazole (DTBT). We describe the synthesis of DTBT monomers with either 0, 1, or 2 cyano groups on the BT unit and their corresponding copolymers with the electron rich donor dithienogermole (DTG). The presence of the cyano group is found to have a strong influence on the optoelectronic properties of the resulting donor–acceptor polymers, with the optical band gap red-shifting by approximately 0.15 eV per cyano substituent. We find that the polymer electron affinity is significantly increased by ∼0.25 eV upon addition of each cyano group, while the ionization potential is less strongly affected, increasing by less than 0.1 eV per cyano substituent. In organic photovoltaic (OPV) devices power conversion efficiencies (PCE) are almost doubled from around 3.5% for the unsubstituted BT polymer to over 6.5% for the monocyano substituted BT polymer. However, the PCE drops to less than 1% for the dicyano substituted BT polymer. These differences are mainly related to differences in the photocurrent, which varies by 1 order of magnitude between the best (1CN) and worst devices (2CN). The origin of this variation in the photocurrent was investigated by studying the charge generation properties of the photoactive polymer–fullerene blends using fluorescence and transient absorption spectroscopic techniques. These measurements revealed that the improved photocurrent of 1CN in comparison to 0CN was due to improved light harvesting properties while maintaining a high exciton dissociation yield. The addition of one cyano group to the BT unit optimized the position of the polymer LUMO level closer to that of the electron acceptor PC71BM, such that the polymer’s light harvesting properties were improved without sacrificing either the exciton dissociation yield or device VOC. We also identify that the dr

Journal article

Kang K, Watanabe S, Broch K, Sepe A, Brown A, Nasrallah I, Nikolka M, Fei Z, Heeney M, Matsumoto D, Marumoto K, Tanaka H, Kuroda SI, Sirringhaus Het al., 2016, 2D coherent charge transport in highly ordered conducting polymers doped by solid state diffusion, Nature Materials, Vol: 15, Pages: 896-902, ISSN: 1476-4660

Doping is one of the most important methods to control charge carrier concentration in semiconductors. Ideally, the introduction of dopants should not perturb the ordered microstructure of the semiconducting host. In some systems, such as modulation-doped inorganic semiconductors or molecular charge transfer crystals, this can be achieved by spatially separating the dopants from the charge transport pathways. However, in conducting polymers, dopants tend to be randomly distributed within the conjugated polymer, and as a result the transport properties are strongly affected by the resulting structural and electronic disorder. Here, we show that in the highly ordered lamellar microstructure of a regioregular thiophene-based conjugated polymer, a small-molecule p-type dopant can be incorporated by solid state diffusion into the layers of solubilizing side chains without disrupting the conjugated layers. In contrast to more disordered systems, this allows us to observe coherent, free-electron-like charge transport properties, including a nearly ideal Hall effect in a wide temperature range, a positive magnetoconductance due to weak localization and the Pauli paramagnetic spin susceptibility.

Journal article

Green J, Han Y, Kilmurray R, McLachlan M, Anthopoulos T, Heeney MJet al., 2016, An Air-Stable Semiconducting Polymer Containing Dithieno[3,2-b:2′,3′-d]arsole, Angewandte Chemie - International Edition, Vol: 55, Pages: 7148-7151, ISSN: 1433-7851

Arsole-containing conjugated polymers are a practically unexplored class of materials despite the high interest in their phosphole analogues. Herein we report the synthesis of the first dithieno[3,2-b;2′,3′-d]arsole derivative, and demonstrate that it is stable to ambient oxidation in its +3 oxidation state. A soluble copolymer is obtained by a palladium-catalyzed Stille polymerization and demonstrated to be a p-type semiconductor with promising hole mobility, which was evaluated by field-effect transistor measurements.

Journal article

Green JP, Han Y, Kilmurray R, McLachlan MA, Anthopoulos TD, Heeney Met al., 2016, An air-stable semiconducting polymer containing Dithieno[3,2- b :2′,3′- d ]arsole, Angewandte Chemie, Vol: 128, Pages: 7264-7267, ISSN: 0044-8249

Arsole-containing conjugated polymers are a practically unexplored class of materials despite the high interest in their phosphole analogues. Herein we report the synthesis of the first dithieno[3,2-b;2′,3′-d]arsole derivative, and demonstrate that it is stable to ambient oxidation in its +3 oxidation state. A soluble copolymer is obtained by a palladium-catalyzed Stille polymerization and demonstrated to be a p-type semiconductor with promising hole mobility, which was evaluated by field-effect transistor measurements.

Journal article

Bannock JH, Xu W, Baïssas T, Heeney M, de Mello JCet al., 2016, Rapid flow-based synthesis of poly(3-hexylthiophene) using 2-methyltetrahydrofuran as a bio-derived reaction solvent, European Polymer Journal, Vol: 80, Pages: 240-246, ISSN: 1873-1945

We report the synthesis of poly(3-hexylthiophene) (P3HT) by Grignard metathesis (GRIM) polymerization using the bio-derived ‘green’ solvent 2-methyltetrahydrofuran (2-MeTHF). Using a standard flask-based reaction, the molecular weight distribution, regioregularity and product yield were found to be similar to those obtained under equivalent conditions using tetrahydrofuran (THF) as a reaction solvent. The synthesis was subsequently adapted to a novel “tube-in-shell” droplet-based flow reactor, using a newly developed high-solubility catalyst derived from nickel(II) bromide ethylene glycol dimethyl ether complex (Ni(dme)Br2) and 1,3-bis(diphenylphosphino)propane (dppp). Use of the new catalyst together with an increased reaction temperature of 65 oC (enabled by the higher boiling point of 2-MeTHF) resulted in an approximate four-fold increase in reaction rate compared to a standard THF- based synthesis at 55 oC, with full conversion reached within one minute. The purified flow- synthesized polymer had an Mw of 46 kg mol-1, a low PDI of 1.4, and a regioregularity of 93 %, indicating the suitability of flow-based GRIM polymerization in 2-MeTHF for the high- throughput synthesis of high quality P3HT.

Journal article

Bannock JH, Treat N, Chabinyc M, Stingelin N, Heeney M, de Mello JCet al., 2016, The influence of polymer purification on the efficiency of poly(3-hexylthiophene):fullerene organic solar cells, Scientific Reports, Vol: 6, ISSN: 2045-2322

We report the influence of different polymer purification procedures on the photovoltaic performance ofbulk heterojunction solar cells formed from binary blends of poly(3-hexylthiophene) (P3HT) andfullerenes. Selective Soxhlet extractions and metal scavenging agents were used to remove residualmonomer, magnesium salt by-products and catalyst from high-weight P3HT (Mw 121 kg/mol, PDI 1.8,RR 99%) synthesised by the Grignard metathesis (GRIM) polymerization route. Using phenyl-C61-butyric acid methyl ester (PC60BM) as an electron acceptor, we observed an increase in average powerconversion efficiency from 2.3 to 4.8 % in going from crude to fully purified material. Using indene-C60bisadduct (IC60BA) in place of PC60BM, we observed a further increase to an average value of 6.6 %,which is high for a bulk heterojunction formed from a binary blend of P3HT and C60 fullerene derivatives.

Journal article

Kassar T, Gueldal NS, Berlinghof M, Ameri T, Kratzer A, Schroeder BC, Li Destri G, Hirsch A, Heeney M, McCulloch I, Brabec CJ, Unruh Tet al., 2016, Real-Time Investigation of Intercalation and Structure Evolution in Printed Polymer:Fullerene Bulk Heterojunction Thin Films, ADVANCED ENERGY MATERIALS, Vol: 6, ISSN: 1614-6832

Journal article

Dimitrov SD, Schroeder BC, Nielsen CB, Bronstein H, Fei Z, McCulloch I, Heeney M, Durrant JRet al., 2016, Singlet Exciton Lifetimes in Conjugated Polymer Films for Organic Solar Cells, Polymers, Vol: 8, ISSN: 2073-4360

The lifetime of singlet excitons in conjugated polymer films is a key factor taken into account during organic solar cell device optimization. It determines the singlet exciton diffusion lengths in polymer films and has a direct impact on the photocurrent generation by organic solar cell devices. However, very little is known about the material properties controlling the lifetimes of singlet excitons, with most of our knowledge originating from studies of small organic molecules. Herein, we provide a brief summary of the nature of the excited states in conjugated polymer films and then present an analysis of the singlet exciton lifetimes of 16 semiconducting polymers. The exciton lifetimes of seven of the studied polymers were measured using ultrafast transient absorption spectroscopy and compared to the lifetimes of seven of the most common photoactive polymers found in the literature. A plot of the logarithm of the rate of exciton decay vs. the polymer optical bandgap reveals a medium correlation between lifetime and bandgap, thus suggesting that the Energy Gap Law may be valid for these systems. This therefore suggests that small bandgap polymers can suffer from short exciton lifetimes, which may limit their performance in organic solar cell devices. In addition, the impact of film crystallinity on the exciton lifetime was assessed for a small bandgap diketopyrrolopyrrole co-polymer. It is observed that the increase of polymer film crystallinity leads to reduction in exciton lifetime and optical bandgap again in agreement with the Energy Gap Law.

Journal article

Cachelin P, Green JP, Peijs T, Heeney M, Bastiaansen CWMet al., 2016, Optical acetone vapor sensors based on chiral nematic liquid crystals and reactive chiral dopants, Advanced Optical Materials, Vol: 4, Pages: 592-596, ISSN: 2195-1071

Accurate monitoring of exposure to organic vapors, such as acetone, is an important part of maintaining a safe working environment and adhering to long- and short-term exposure limits. Here, a novel acetone vapor detection system is described based on the use of a reactive chiral dopant in a nematic liquid crystal thin film, which can accurately monitor the total exposure over a given time frame through changes in the reflection band of the film. It is found that films exposed to 1000 parts per million by volume (ppmv) of acetone vapor for 2 h exhibit a shift in reflection band of 12 nm, with smaller shifts observed at lower concentrations of acetone. Such sensors have potential applications in industrial hygiene.

Journal article

Xue X, Chandler G, Zhang X, Kline RJ, Fei Z, Heeney M, Diemer PJ, Jurchescu OD, O'Connor BTet al., 2015, Oriented Liquid Crystalline Polymer Semiconductor Films with Large Ordered Domains, ACS APPLIED MATERIALS & INTERFACES, Vol: 7, Pages: 26726-26734, ISSN: 1944-8244

Journal article

Snyder CR, Kline RJ, DeLongchamp DM, Nieuwendaal RC, Richter LJ, Heeney M, McCulloch Iet al., 2015, Classification of Semiconducting Polymeric Mesophases to Optimize Device Postprocessing, JOURNAL OF POLYMER SCIENCE PART B-POLYMER PHYSICS, Vol: 53, Pages: 1641-1653, ISSN: 0887-6266

Journal article

Collado Fregoso E, Boufflet P, Fei Z, Gann E, Ashraf S, Li Z, McNeill C, Durrant J, Heeney Met al., 2015, Increased Exciton Dipole Moment Translates into Charge-transfer Excitons in Thiophene-fluorinated Low-bandgap Polymers for Organic Photovoltaic Applications, Chemistry of Materials, Vol: 27, Pages: 7934-7944, ISSN: 1520-5002

In this study, we investigate the role of thiophene fluorination in a low-bandgap polymer for organic photovoltaic applications. We use a combined theoretical and experimental approach to investigate charge generation and recombination dynamics, and their correlation with blend microstructure and polymer dipole moment. We find that fluorination results in an increased change in the dipole moment upon exciton formation, which is correlated with the appearance of charge-transfer excitons, as evidenced from ultrafast transient absorption studies. Fluorination also results in smaller yet purer domains, evidenced by atomic force microscopy and resonant soft X-ray scattering, and in agreement with photoluminescence quenching measurements. This change in film morphology is correlated with a modest retardation of nongeminate recombination losses. The efficient charge generation and slower recombination are likely to be partly responsible for the enhanced device efficiency in the fluorinated polymer/fullerene devices.

Journal article

Al-Hashimi M, Han Y, Smith J, Bazzi HS, Alqaradawi SYA, Watkins SE, Anthopoulos TD, Heeney Met al., 2015, Influence of the heteroatom on the optoelectronic properties and transistor performance of soluble thiophene-, selenophene- and tellurophene-vinylene copolymers, Chemical Science, Vol: 7, Pages: 1093-1099, ISSN: 2041-6539

We report the first soluble poly(3-dodecyl tellurophenylene-vinylene) polymer (P3TeV) by Stille copolymerization and compare its properties to the analogous thiophene and selenophene containing polymers. The optical band gap of the polymers is shown to systematically decrease as the size of the heteroatom is increased, mainly as a result of a stabilization of the LUMO energy, resulting in a small band gap of 1.4 eV for P3TeV. Field effect transistors measurements in variety of architectures demonstrate that the selenophene polymer exhibits the highest mobility, highlighting that increasing the size of the heteroatom is not always beneficial for charge transport.

Journal article

Heeney MJ, Han Y, Fei Z, McCulloch I, Stingelin N, Treat N, Anthopoulos T, Faber H, Zhang W, Zhu X, Feng Yet al., 2015, A Novel Alkylated Indacenodithieno[3,2-b]thiophene-based Polymer for High-performance Field Effect Transistors, Advanced Materials, Vol: 28, Pages: 3922-3927, ISSN: 1521-4095

A novel rigid donor monomer, indacenodithieno[3,2-b]thiophene (IDTT), containing linear alkyl chains is reported. Its copolymer with benzothiadiazole is an excellent p-type semiconductor, affording a mobility of 6.6 cm² V⁻¹ s⁻¹ in top-gated field-effect transistors with pentafluorobenzenethiol-modified Au electrodes. Electrode treatment with solution-deposited copper(I) thiocyanate (CuSCN) has a beneficial hole-injection/electron-blocking effect, further enhancing the mobility to 8.7 cm² V⁻¹ s⁻¹.

Journal article

Boufflet P, Han Y, Fei Z, Treat ND, Li R, Smilgies D-M, Stingelin N, Anthopoulos TD, Heeney MJet al., 2015, Using Molecular Design to Increase Hole Transport: Backbone Fluorination in the Benchmark Material Poly(2,5-bis(3-alkylthiophen-2-yl)thieno[3,2-b]-thiophene (pBTTT), Advanced Functional Materials, Vol: 25, Pages: 7038-7048, ISSN: 1616-3028

The synthesis of a novel 3,3'-difluoro-4,4'-dihexadecyl-2,2'-bithiophene monomer and its copolymerisation with thieno[3,2-b]thiophene to afford the fluorinated analogue of the well-known poly(2,5-bis(3-alkylthiophen-2-yl)thieno[3,2-b]-thiophene) (PBTTT) polymer is reported. Fluorination is found to have a significant influence on the physical properties of the polymer, enhancing aggregation in solution and increasing melting point by over 100 °C compared to non-fluorinated polymer. On the basis of DFT calculations these observations are attributed to inter- and intra-molecular S…F interactions. As a consequence, the fluorinated polymer PFBTTT exhibits a four-fold increase in charge carrier mobility compared to the non-fluorinated polymer and excellent ambient stability for a non-encapsulated transistor device.

Journal article

Casey A, Han Y, Wyatt MF, Anthopoulos TD, Heeney Met al., 2015, Novel soluble thieno[3,2-b]thiophene fused porphyrazine, RSC Advances, Vol: 5, Pages: 90645-90650, ISSN: 2046-2069

The synthesis of the first soluble thieno[3,2-b]thiophene based porphyrazine (ZnTTPz) is reported from the cyclisation of 2,3-dicyano-5-octylthieno[3,2-b]thiophene. ZnTTPz can be considered the all thiophene analogue of naphthalocyanine. ZnTTPz exhibits a red-shifted absorption in solution and thin film, as well as a reduced band gap in comparison to the thiophene analogue due to an increased conjugation length. Films of ZnTTPz processed from solution exhibit p-type semiconducting behaviour in field-effect transistors with low hysteresis and reasonable charge carrier mobility.

Journal article

Campbell AJ, Higgins SG, Muir BVO, Heeney Met al., 2015, Indacenodithiophene–benzothiadiazole organic field-effect transistorswith gravure-printed semiconductor and dielectric on plastic, MRS Communications, Vol: 5, Pages: 599-603, ISSN: 2159-6867

We demonstrate the gravure printing of a high-performance indacenodithiophene (IDT) copolymer, indacenodithiophene–benzothiadiazole (C16IDT–BT), onto self-aligned organic field-effect transistor architectures on flexible plastic substrates. We observed that the combination of a gravure-printed dielectric with gravure-printed semiconductor yielded devices with higher mean-effective mobility than devices manufactured using photolithographically patterned dielectric. Peak mobilities of μ = 0.1 cm2 V−1 s−1 were measured, and exceed previous reports for non-printed C16IDT-BT on non-flexible silicon substrates.

Journal article

Andemach R, Utzat H, Dimitrov SD, McCulloch I, Heeney M, Durrant JR, Bronstein Het al., 2015, Synthesis and Exciton Dynamics of Triplet Sensitized Conjugated Polymers, JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, Vol: 137, Pages: 10383-10390, ISSN: 0002-7863

Journal article

Gruber M, Jung S-H, Schott S, Venkateshvaran D, Kronemeijer AJ, Andreasen JW, McNeill CR, Wong WWH, Shahid M, Heeney M, Lee J-K, Sirringhaus Het al., 2015, Enabling high-mobility, ambipolar charge-transport in a DPP-benzotriazole copolymer by side-chain engineering, Chemical Science, Vol: 6, Pages: 6949-6960, ISSN: 2041-6539

In this article we discuss the synthesis of four new low band-gap co-polymers based on the diketopyrrolopyrrole (DPP) and benzotriazole (BTZ) monomer unit. We demonstrate that the BTZ unit allows for additional solubilizing side-chains on the co-monomer and show that the introduction of a linear side-chain on the DPP-unit leads to an increase in thin-film order and charge-carrier mobility if a sufficiently solubilizing, branched, side chain is attached to the BTZ. We compare two different synthetic routes, direct arylation and Suzuki-polycondensation, by a direct comparison of polymers obtained via the two routes and show that direct arylation produces polymers with lower electrical performance which we attribute to a higher density of chain Furthermore we demonstrate that a polymer utilizing this design motif and synthesized via Suzuki-polycondensation ((l-C18)-DPP-(b-C17)-BTZ) exhibits exceptionally high and near balanced average electron and hole mobilities >2 cm2 V−1 s−1 which are among the highest, robustly extracted mobility values reported for DPP copolymers in a top-gate configuration to date. Our results demonstrate clearly that linear side chain substitution of the DPP unit together with co-monomers that allow for the use of sufficiently long or branched solubilizing side chains can be an attractive design motif for solution processable, high mobility DPP copolymers.

Journal article

Zhong H, Han Y, Shaw J, Anthopoulos TD, Heeney Met al., 2015, Fused ring cyclopentadithienothiophenes as novel building blocks for high field effect mobility conjugated polymers, Macromolecules, Vol: 48, Pages: 5605-5613, ISSN: 0024-9297

Journal article

Hu H, Zhao K, Fernandes N, Boufflet P, Bannock JH, Yu L, de Mello JC, Stingelin N, Heeney M, Giannelise EP, Amassian Aet al., 2015, Entanglements in marginal solutions: a means of tuning pre-aggregation of conjugated polymers with positive implications for charge transport, Journal of Materials Chemistry C, Vol: 3, Pages: 7394-7404, ISSN: 2050-7534

The solution-processing of conjugated polymers, just like commodity polymers, is subject to solvent and molecular weight-dependent solubility, interactions and chain entanglements within the polymer, all of which can influence the crystallization and microstructure development in semi-crystalline polymers and consequently affect charge transport and optoelectronic properties. Disentanglement of polymer chains in marginal solvents was reported to work via ultrasonication, facilitating the formation of photophysically ordered polymer aggregates. In this contribution, we explore how a wide range of technologically relevant solvents and formulations commonly used in organic electronics influence chain entanglement and the aggregation behaviour of P3HT using a combination of rheological and spectrophotometric measurements. The specific viscosity of the solution offers an excellent indication of the degree of entanglements in the solution, which is found to be related to the solubility of P3HT in a given solvent. Moreover, deliberately disentangling the solution in the presence of solvophobic driving forces, leads consistently to formation of photophysically visible aggregates which is indicative of local and perhaps long range order in the solute. We show for a broad range of solvents and molecular weights that disentanglement ultimately leads to significant ordering of the polymer in the solid state and a commensurate increase in charge transport properties. In doing so we demonstrate a remarkable ability to tune the microstructure which has important implications for transport properties. We discuss its potential implications in the context of organic electronics and photovoltaics.

Journal article

Fei Z, Boufflet P, Wood S, Wade J, Moriarty J, Gann E, Ratcliff EL, McNeill CR, Sirringhaus H, Kim JS, Heeney Met al., 2015, Influence of backbone fluorination in regioregular poly(3-alkyl-4-fluoro)thiophenes., Journal of the American Chemical Society, Vol: 137, Pages: 6866-6879, ISSN: 1520-5126

We report two strategies toward the synthesis of 3-alkyl-4-fluorothiophenes containing straight (hexyl and octyl) and branched (2-ethylhexyl) alkyl groups. We demonstrate that treatment of the dibrominated monomer with 1 equiv of alkyl Grignard reagent leads to the formation of a single regioisomer as a result of the pronounced directing effect of the fluorine group. Polymerization of the resulting species affords highly regioregular poly(3-alkyl-4-fluoro)thiophenes. Comparison of their properties to those of the analogous non-fluorinated polymers shows that backbone fluorination leads to an increase in the polymer ionization potential without a significant change in optical band gap. Fluorination also results in an enhanced tendency to aggregate in solution, which is ascribed to a more co-planar backbone on the basis of Raman and DFT calculations. Average charge carrier mobilities in field-effect transistors are found to increase by up to a factor of 5 for the fluorinated polymers.

Journal article

Buchaca-Domingo E, Vandewal K, Fei Z, Watkins SE, Scholes FH, Bannock JH, de Mello JC, Richter LJ, DeLongchamp DM, Amassian A, Heeney M, Salleo A, Stingelin Net al., 2015, Direct Correlation of Charge Transfer Absorption with Molecular Donor:Acceptor Interfacial Area via Photothermal Deflection Spectroscopy, JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, Vol: 137, Pages: 5256-5259, ISSN: 0002-7863

Journal article

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