Publications
228 results found
Martin J, Iturrospe A, Cavallaro A, et al., 2017, Relaxations and relaxor-ferroelectric-like response of nanotubularly confined poly(vinylidene fluoride), Chemistry of Materials, Vol: 29, Pages: 3515-3525, ISSN: 1520-5002
Herein, we elucidate the impact of tubular confinement on the structure and relaxation behavior of poly(vinylidene difluoride) (PVDF) and how these affect the para-/ferroelectric behavior of this polymer. We use PVDF nanotubes that were solidified in anodic aluminum oxide (AAO) templates. Dielectric spectroscopy measurements evidence a bimodal relaxation process for PVDF nanotubes: besides the bulk-like α-relaxation, we detect a notably slower relaxation that is associated with the PVDF regions of restricted dynamics at the interface with the AAO pore. Strikingly, both the bulk-like and the interfacial relaxation tend to become temperature independent as the temperature increases, a behavior that has been observed before in inorganic relaxor ferroelectrics. In line with this, we observe that the real part of the dielectric permittivity of the PVDF nanotubes exhibits a broad maximum when plotted against the temperature, which is, again, a typical feature of relaxor ferroelectrics. As such, we propose that, in nanotubular PVDF, ferroelectric-like nanodomains are formed in the amorphous phase regions adjacent to the AAO interface. These ferroelectric nanodomains may result from an anisotropic chain conformation and a preferred orientation of local dipoles due to selective H-bond formation between the PVDF macromolecues and the AAO walls. Such relaxor-ferroelectric-like behavior has not been observed for nonirradiated PVDF homopolymer; our findings thus may enable in the future alternative applications for this bulk commodity plastic, e.g., for the production of electrocaloric devices for solid-state refrigeration which benefit from a relaxor-ferroelectric-like response.
Martin J, Zhao D, Lenz T, et al., 2017, Solid-state-processing of delta-PVDF, Materials Horizons, Vol: 4, Pages: 408-414, ISSN: 2051-6355
Poly(vinylidene fluoride) (PVDF) has long been regarded as an ideal piezoelectric ‘plastic’ because it exhibits a large piezoelectric response and a high thermal stability. However, the realization of piezoelectric PVDF elements has proven to be problematic due to, amongst other reasons, the lack of industrially scalable methods to process PVDF into the appropriate polar crystalline forms. Here, we show that fully piezoelectric PVDF films can be produced via a single-step process that exploits the fact that PVDF can be molded at temperatures below its melting temperature, i.e. via solid-state-processing. We demonstrate that we thereby produce δ-PVDF, the piezoelectric charge coefficient of which is comparable to that of biaxially stretched β-PVDF. We expect that the simplicity and scalability of solid-state processing combined with the excellent piezoelectric properties of our PVDF structures will provide new opportunities for this commodity polymer and will open a range of possibilities for future, large-scale, industrial production of plastic piezoelectric films.
Botiz I, Codescu M-A, Farcau C, et al., 2017, Convective self-assembly of pi-conjugated oligomers and polymers, JOURNAL OF MATERIALS CHEMISTRY C, Vol: 5, Pages: 2513-2518, ISSN: 2050-7526
Razzell-Hollis J, Fleischli F, Jahnke AA, et al., 2017, Effects of side-chain length and shape on polytellurophene molecular order and blend morphology, Journal of Physical Chemistry C, Vol: 121, Pages: 2088-2098, ISSN: 1932-7447
We investigate the molecular order and thin film morphology of the conjugated polymer polytellurophene, in order to understand how the tellurium atom and the choice of side-chain influence the conjugated polymer’s backbone planarity and performance in organic transistors. We find that poly(3hexyltellurophene) (P3HTe) continues the trend from polythiophene (P3HT) to polyselenophene (P3HS): substitution with Tellurium leads to a more planar backbone, evident from the shifts of the C═C vibrational peak to lower wavenumbers (∼1389 cm–1) and a smaller optical band gap (∼1.4 eV). Resonant Raman spectroscopy revealed that molecular order was highly dependent on the structure of the P3ATe alkyl side-chain: a longer chains introduces kinetic hindrance, reducing the fraction of ordered phase obtained at room temperature, while a branched side-chain introduces steric hindrance, with intrinsic disorder present even when deposited at higher temperatures. When blended with the insulator HDPE, all three polymers exhibit little additional disorder and instead form phase-separated networks of high molecular order that are beneficial to percolated charge transport in transistors. We find that molecular order, as measured by Raman, correlates well with reported transistor mobilities and provides a greater understanding of the structure–property relationships that determine the performance of these novel organometallic polymers in electronic devices.
Botiz I, Leordean C, Stingelin N, 2017, Structural Control in Polymeric Semiconductors: Application to the Manipulation of Light-emitting Properties, SEMICONDUCTING POLYMERS: CONTROLLED SYNTHESIS AND MICROSTRUCTURE, Editors: Luscombe, Publisher: ROYAL SOC CHEMISTRY, Pages: 187-218, ISBN: 978-1-78262-034-1
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- Citations: 2
Westacott P, Treat ND, Martin J, et al., 2016, Origin of fullerene-induced vitrification of fullerene: donor polymer photovoltaic blends and its impact on solar cell performance, Journal of Materials Chemistry A, Vol: 5, Pages: 2689-2700, ISSN: 2050-7488
Organic solar cell blends comprised of an electron donating polymer and electron accepting fullerene typically form upon solution casting a thin-film structure made up of a complex mixture of phases. These phases can vary greatly in: composition, order and thermodynamic stability; and they are dramatically influenced by the processing history. Understanding the processes that govern the formation of these phases and their subsequent effect on the efficiency of photo-generating and extracting charge carriers is of utmost importance to enable rational design and processing of these blends. Here we show that the vitrifying effect of three fullerene derivatives ([60]PCBM, bis[60]PCBM, and [60]ICBA) on the prototypical donor polymer (rr-P3HT) can dominate microstructure formation of fullerene/donor polymer blends cast from solution. Using a dynamic crystallization model based on an amalgamation of Flory–Huggins and Lauritzen–Hoffman theory coupled to solvent evaporation we demonstrate that this vitrification, which can result in a large fraction of highly intermixed amorphous solid solution of the fullerene and the polymer, is due to kinetic and thermodynamic reasons. The former is partly determined by the glass transition temperature of the individual components while donor polymer:fullerene miscibility, strongly influenced by the chemical nature of the donor and the fullerene and leading to thermodynamic mixing, dictates the second phenomena. We show that our approximate dynamic crystallization model assists understanding the different solid-state structure formation of rr-P3HT:fullerene blends. Due to the generality of the assumptions used, our model should be widely applicable and assist to capture the influence of the different vitrification mechanisms also of other photovoltaic blends, including the high-efficiency systems based on the strongly aggregating PCE11 (PffBT4T-2OD), which also feature clear signs of vitirfication upon blending with, e.g., [60
Pacheco-Moreno CM, Schreck M, Scaccabarozzi AD, et al., 2016, The importance of materials design to make ions flow: toward novel materials platforms for bioelectronics applications, Advanced Materials, Vol: 29, ISSN: 0935-9648
Chemical design criteria for materials for bioelectronics applications using a series of copolymer derivatives based on poly(3-hexylthiophene) are established. Directed chemical design via side-chain functionalization with polar groups allows manipulation of ion transport and ion-to-electron transduction. Insights gained will permit increased use of the plethora of materials employed in the organic electronics area for application in the bioelectronics field.
Causa M, De Jonghe-Risse J, Scarongella M, et al., 2016, The fate of electron–hole pairs in polymer:fullerene blends for organic photovoltaics, Nature Communications, Vol: 7, ISSN: 2041-1723
There has been long-standing debate on how free charges are generated in donor:acceptor blends that are used in organic solar cells, and which are generally comprised of a complex phase morphology, where intermixed and neat phases of the donor and acceptor material co-exist. Here we resolve this question, basing our conclusions on Stark effect spectroscopy data obtained in the absence and presence of externally applied electric fields. Reconciling opposing views found in literature, we unambiguously demonstrate that the fate of photogenerated electron–hole pairs—whether they will dissociate to free charges or geminately recombine—is determined at ultrafast times, despite the fact that their actual spatial separation can be much slower. Our insights are important to further develop rational approaches towards material design and processing of organic solar cells, assisting to realize their purported promise as lead-free, third-generation energy technology that can reach efficiencies over 10%.
Fei Z, Han Y, Martin J, et 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.
Bovo G, Bräunlich I, Caseri WR, et al., 2016, Room temperature dielectric bistability in solution-processed spin crossover polymer thin films, Journal of Materials Chemistry C, Vol: 4, Pages: 6240-6248, ISSN: 2050-7534
The spin crossover (SCO) phenomena are a remarkable example of spin-state switching at the molecular level. The low- and high-spin states can be reversibly selected through application of external stimulus-often simply a variation in temperature. Since the particular spin-state embodies optical, electronic and structural characteristics, the spin switching can be readily detected or probed using a variety of techniques. In this regard, SCO phenomena show great promise for a range of devices. The key to this uptake is the preparation of high-quality, thin-films capable of retaining SCO properties, and solution-based materials, in particular, provide further opportunities for integration or blending with other functional materials. The present work examines SCO behaviour from two iron(ii)-triazole polymers, with short and long side chains, prepared and investigated in a variety of formats-from bulk powders to thick and thin films. Magnetic, optical and electronic techniques all verify the SCO behaviour is faithfully maintained for all formats. The two materials serve to highlight the impact on key properties arising from the different density of Fe atoms. The results, all from solution-based materials, are extremely promising and clearly emphasise the growing capabilities and processing advances associated with SCO compounds.
Harkin DJ, Broch K, Schreck M, et al., 2016, Decoupling Charge Transport and Electroluminescence in a High Mobility Polymer Semiconductor, Advanced Materials, Vol: 28, Pages: 6378-6385, ISSN: 1521-4095
Fluorescence enhancement of a high mobility polymer semiconductor is achieved via energy transfer to a higher fluorescence quantum yield squaraine dye molecule on 50 ps timescales. In organic light emitting diodes an order of magnitude enhancement of the external quantum efficiency is observed without reduction in the charge carrier mobility resulting in radiances of up to 5 W str(-1) m(-2) at 800 nm.
Le Borgne M, Quinn J, Martin J, et al., 2016, Synthesis and properties of a novel narrow band gap oligomeric diketopyrrolopyrrole-based organic semiconductor, Dyes and Pigments, Vol: 131, Pages: 160-167, ISSN: 1873-3743
A trimer of diketopyrrolopyrole (DPP), Tri-BTDPP, was synthesized and characterized. Tri-BTDPP has a HOMO level of −5.34 eV, a low band gap of 1.33 eV, and a hole mobility of ∼10−3 cm2 V−1 s−1 in organic field effect transistors (OFETs). Organic photovoltaic (OPV) devices using the donor/acceptor blends of Tri-BTDPP and PC71BM exhibited low power conversion efficiencies (PCE) of up to 0.72%, even though the desirable optical and electronic characteristics of this compound as a donor semiconductor for achieving high performance for OPV. Through an intensive study of the active layer using AFM, XRD, and DSC, it was found that Tri-BTDPP and PC71BM were unable to intermix and formed oversized Tri-BTDPP phases, resulting in poor charge separation. Some guidance on how to improve the OPV performance of Tri-DPP compounds is provided.
Bannock JH, Treat N, Chabinyc M, et 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.
Stingelin N, 2016, On the role of intermixed phases in organic photovoltaic blends, Publisher: AMER CHEMICAL SOC, ISSN: 0065-7727
Stingelin N, 2016, Printed electronics and photonics: Future challenges and opportunities provided by multicomponent systems, Publisher: AMER CHEMICAL SOC, ISSN: 0065-7727
Lazzerini GM, Paterno GM, Tregnago G, et al., 2016, Traceable atomic force microscopy of high-quality solvent-free crystals of [6,6]-phenyl-C61-butyric acid methyl ester, Applied Physics Letters, Vol: 108, ISSN: 1077-3118
We report high-resolution, traceable atomic force microscopymeasurements of high-quality, solvent-free single crystals of [6,6]-phenyl-C61-butyric acid methyl ester (PCBM). These were grown by drop-casting PCBM solutions onto the spectrosil substrates and by removing the residual solvent in a vacuum. A home-built atomic force microscope featuring a plane mirror differential optical interferometer, fiber-fed from a frequency-stabilized laser (emitting at 632.8 nm), was used to measure the crystals' height. The optical interferometer together with the stabilized laser provides traceability (via the laser wavelength) of the vertical measurements made with the atomic force microscope. We find that the crystals can conform to the surface topography, thanks to their height being significantly smaller compared to their lateral dimensions (namely, heights between about 50 nm and 140 nm, for the crystals analysed, vs. several tens of microns lateral dimensions). The vast majority of the crystals are flat, but an isolated, non-flat crystal provides insights into the growth mechanism and allows identification of “molecular terraces” whose height corresponds to one of the lattice constants of the single PCBM crystal (1.4 nm) as measured with X-ray diffraction.
Botiz I, Astilean S, Stingelin N, 2016, Altering the emission properties of conjugated polymers, POLYMER INTERNATIONAL, Vol: 65, Pages: 157-163, ISSN: 0959-8103
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- Citations: 21
Martin Perez J, Scaccabarozzi AD, Nogales A, et al., 2016, Confinement effects on the crystalline features of poly(9,9-dioctylfluorene), European Polymer Journal, Vol: 81, Pages: 650-660, ISSN: 0014-3057
AbstractTypical device architectures in polymer-based optoelectronic devices, such as field effect transistors organic light emitting diodes and photovoltaic cells include sub-100 nm semiconducting polymer thin-film active layers, whose microstructure is likely to be subject to finite-size effects. The aim of this study was to investigate effect of the two-dimensional spatial confinement on the internal structure of the semiconducting polymer poly(9,9-dioctylfluorene) (PFO). PFO melts were confined inside the cylindrical nanopores of anodic aluminium oxide (AAO) templates and crystallized via two crystallization strategies, namely, in the presence or in the absence of a surface bulk reservoir located at the template surface. We show that highly textured semiconducting nanowires with tuneable crystal orientation can be thus produced. The results presented here demonstrate the simple fabrication and crystal engineering of ordered arrays of PFO nanowires; a system with potential applications in devices where anisotropic optical properties are required, such as polarized electroluminescence, waveguiding, optical switching and lasing.
Treat ND, Westacott P, Stingelin N, 2016, ORGANIC SEMICONDUCTORS: MANIPULATION AND CONTROL OF THE MICROSTRUCTURE OF ACTIVE LAYERS, WSPC REFERENCE ON ORGANIC ELECTRONICS: ORGANIC SEMICONDUCTORS, VOL: 2: FUNDAMENTAL ASPECTS OF MATERIALS AND APPLICATIONS, Editors: Bredas, Marder, Publisher: WORLD SCIENTIFIC PUBL CO PTE LTD, Pages: 159-193
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- Citations: 2
Abdelsamie M, Treat ND, Zhao K, et al., 2015, Toward Additive-Free Small-Molecule Organic Solar Cells: Roles of the Donor Crystallization Pathway and Dynamics, ADVANCED MATERIALS, Vol: 27, Pages: 7285-+, ISSN: 0935-9648
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- Citations: 55
Heeney MJ, Han Y, Fei Z, et 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.
Boufflet P, Han Y, Fei Z, et 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.
Lenz T, Zhao D, Richardson G, et al., 2015, Microstructured organic ferroelectric thin film capacitors by solution micromolding, PHYSICA STATUS SOLIDI A-APPLICATIONS AND MATERIALS SCIENCE, Vol: 212, Pages: 2124-2132, ISSN: 1862-6300
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- Citations: 13
Galliani D, Mascheroni L, Sassi M, et al., 2015, Thermochromic Latent-Pigment-Based Time-Temperature Indicators for Perishable Goods, ADVANCED OPTICAL MATERIALS, Vol: 3, Pages: 1164-1168, ISSN: 2195-1071
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- Citations: 28
Treat ND, Yaacobi-Gross N, Faber H, et al., 2015, Copper thiocyanate: An attractive hole transport/extraction layer for use in organic photovoltaic cells, Applied Physics Letters, Vol: 107, ISSN: 1077-3118
We report the advantageous properties of the inorganic molecular semiconductor copper(I)thiocyanate (CuSCN) for use as a hole collection/transport layer (HTL) in organic photovoltaic(OPV) cells. CuSCN possesses desirable HTL energy levels [i.e., valence band at 5.35 eV,0.35 eV deeper than poly(3,4-ethylenedioxythiophene):polystyrenesulfonate (PEDOT:PSS)], whichproduces a 17% increase in power conversion efficiency (PCE) relative to PEDOT:PSS-baseddevices. In addition, a two-fold increase in shunt resistance for the solar cells measured in dark conditionsis achieved. Ultimately, CuSCN enables polymer:fullerene based OPV cells to achievePCE > 8%. CuSCN continues to offer promise as a chemically stable and straightforward replacementfor the commonly used PEDOT:PSS.
Schroeder BC, Nielsen CB, Westacott P, et al., 2015, Effects of alkyl chain positioning on conjugated polymer microstructure and field-effect mobilities, MRS Communications, Vol: 5, Pages: 435-440, ISSN: 2159-6867
Ma J, Meng J, Simonet M, et al., 2015, Biodegradable fibre scaffolds incorporating water-soluble drugs and proteins, JOURNAL OF MATERIALS SCIENCE-MATERIALS IN MEDICINE, Vol: 26, ISSN: 0957-4530
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- Citations: 8
Hu H, Zhao K, Fernandes N, et 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.
Song Y, Hellmann C, Stingelin N, et al., 2015, The separation of vibrational coherence from ground- and excited-electronic states in P3HT film, JOURNAL OF CHEMICAL PHYSICS, Vol: 142, ISSN: 0021-9606
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- Citations: 54
Himmelberger S, Duong DT, Northrup JE, et al., 2015, Role of Side-Chain Branching on Thin-Film Structure and Electronic Properties of Polythiophenes, ADVANCED FUNCTIONAL MATERIALS, Vol: 25, Pages: 2616-2624, ISSN: 1616-301X
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- Citations: 62
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