163 results found
Marsh AV, Little M, Cheetham NJ, et al., 2020, Highly Deformed o-Carborane Functionalised Non-linear Polycyclic Aromatics with Exceptionally Long C-C Bonds, CHEMISTRY-A EUROPEAN JOURNAL, Vol: 27, Pages: 1970-1975, ISSN: 0947-6539
Cheetham NJ, Ortiz M, Pereyedentsev A, et al., 2019, The Importance of Microstructure in Determining Polaron Generation Yield in Poly(9,9-dioctylfluorene), CHEMISTRY OF MATERIALS, Vol: 31, Pages: 6787-6797, ISSN: 0897-4756
Dyson MJ, Lariou E, Martin J, et al., 2019, Managing Local Order in Conjugated Polymer Blends via Polarity Contrast, CHEMISTRY OF MATERIALS, Vol: 31, Pages: 6540-6547, ISSN: 0897-4756
Lubert-Perquel D, Salvadori E, Dyson M, et al., 2018, Identifying triplet pathways in dilute pentacene films, Nature Communications, Vol: 9, Pages: 1-10, ISSN: 2041-1723
Building efficient triplet-harvesting layers for photovoltaic applications requires a deep understanding of the microscopic properties of the components involved and their dynamics. Singlet fission is a particularly appealing mechanism as it generates two excitons from a single photon. However, the pathways of the coupled triplets into free species, and their dependence on the intermolecular geometry, has not been fully explored. In this work, we produce highly ordered dilute pentacene films with distinct parallel and herringbone dimers and aggregates. Using electron paramagnetic resonance spectroscopy, we provide compelling evidence for the formation of distinct quintet excitons in ambient conditions, with intrinsically distinctive electronic and kinetic properties. We find that the ability of quintets to separate into free triplets is promoted in the parallel dimers and this provides molecular design rules to control the triplets, favouring either enhanced photovoltaic efficiency (parallel) or strongly bound pairs that could be exploited for logic applications (herringbone).
Boufflet P, Bovo G, Occhi L, et al., 2018, The influence of backbone fluorination on the dielectric constant of conjugated polythiophenes, Advanced Electronic Materials, Vol: 4, ISSN: 2199-160X
The ability to modify or enhance the dielectric constant of semiconducting polymers can prove valuable for a range of optoelectronic and microelectronic applications. In the case of organic photovoltaics, increasing the dielectric constant of the active layer has often been suggested as a method to control charge generation, recombination dynamics, and ultimately, the power conversion efficiencies. In this contribution, the impact that the degree and pattern of fluorination has on the dielectric constant of poly(3-octylthiophene) (P3OT), a more soluble analogue of the widely studied conjugated material poly(3-hexylthiophene), is explored. P3OT and its backbone-fluorinated analogue, F-P3OT, are compared along with a block and alternating copolymer version of these materials. It is found that the dielectric constant of the polymer thin films increases as the degree of backbone fluorination increases, in a trend consistent with density functional theory calculations of the dipole moment.
Marsh AV, Cheetham NJ, Little M, et al., 2018, Carborane‐Induced Excimer Emission of Severely Twisted Bis‐ o ‐Carboranyl Chrysene, Angewandte Chemie, Vol: 130, Pages: 10800-10805, ISSN: 0044-8249
Heeney MJ, Stavrinou P, Anthony S, et al., 2018, Carborane induced excimer emission of severely twisted Bis-o-carboranyl chrysene, Angewandte Chemie, Vol: 57, Pages: 10640-10645, ISSN: 1521-3757
The synthesis of a highly twisted chrysene derivative incorporating two electron deficient o‐carboranyl groups is reported. The molecule exhibits a complex, excitation‐dependent photoluminescence, including aggregation‐induced emission (AIE) with good quantum efficiency and an exceptionally long singlet excited state lifetime. Through a combination of detailed optical studies and theoretical calculations, the excited state species are identified, including an unusual excimer induced by the presence of o‐carborane. This is the first time that o‐carborane has been shown to induce excimer formation ab initio, as well as the first observation of excimer emission by a chrysene‐based small molecule in solution. Bis‐o‐carboranyl chrysene is thus an initial member of a new family of o‐carboranyl phenacenes exhibiting a novel architecture for highly‐efficient multi‐luminescent fluorophores.
Hamilton I, Chander N, Cheetham NJ, et al., 2018, Controlling molecular conformation for highly efficient and stable deep-blue copolymer light-emitting diodes, ACS Applied Materials and Interfaces, Vol: 10, Pages: 11070-11082, ISSN: 1944-8244
We report a novel approach to the achievement of deep-blue, high-efficiency, and long-lived solution processed polymer light-emitting diodes (PLEDs) via a simple molecular-level conformation change whereby we introduce rigid β-phase segments into a 95% fluorene - 5% arylamine copolymer emission layer (EML). The arylamine moieties at low density act as efficient exciton formation sites in PLEDs whilst the conformational change alters the nature of the dominant luminescence from a broad, charge-transfer like emission to a significantly blue-shifted and highly vibronically structured, excitonic emission. As a consequence, we observe a significant improvement in Commission International de L'Eclairage (CIE) (x, y) co-ordinates from (0.149, 0.175) to (0.145, 0.123) whilst maintaining high efficiency and improving stability. We achieve peak luminous efficiency, η = 3.60 cd/A and luminous power efficiency, ηw = 2.44 lm/W; values that represent state of the art performance for single copolymer deep-blue PLEDs. These values are five-fold better than for otherwise-equivalent, β-phase poly(9,9-dioctylfluorene) (PFO) EML PLEDs (0.70 cd/A and 0.38 lm/W). This report represents the first demonstration of the use of molecular conformation as a vector to control the optoelectronic properties of a fluorene copolymer; previous examples have been confined to homopolymers.
Lin J-Y, Liu B, Yu M-N, et al., 2018, Systematic investigation of self-organization behavior in supramolecular pi-conjugated polymer for multi-color electroluminescence, JOURNAL OF MATERIALS CHEMISTRY C, Vol: 6, Pages: 1535-1542, ISSN: 2050-7526
Braendle A, Perevedentsev A, Cheetham NJ, et al., 2017, Polymers with exceptional photoluminescence by homoconjugation, Chimia (Aarau), Vol: 71, Pages: 733-733, ISSN: 0009-4293
Lin J-Y, Liu B, Yu M-N, et al., 2017, Understanding the molecular gelation processes of heteroatomic conjugated polymers for stable blue polymer light-emitting diodes, JOURNAL OF MATERIALS CHEMISTRY C, Vol: 5, Pages: 6762-6770, ISSN: 2050-7526
Braendle A, Perevedentsev A, Cheetham NJ, et al., 2017, Homoconjugation in Poly(Phenylene Methylene) s: A Case Study of Non-pi-Conjugated Polymers with Unexpected Fluorescent Properties, JOURNAL OF POLYMER SCIENCE PART B-POLYMER PHYSICS, Vol: 55, Pages: 707-720, ISSN: 0887-6266
Gregoire P, Vella E, Dyson M, et al., 2017, Excitonic coupling dominates the homogeneous photoluminescence excitation linewidth in semicrystalline polymeric semiconductors, PHYSICAL REVIEW B, Vol: 95, ISSN: 2469-9950
Dimmock JAR, Kauer M, Mellor AV, et al., 2017, Current voltage characteristics of a metallic structure for a hot-carrier photovoltaic cell, Pages: 993-998
We demonstrate a solar cell based on a thin layer of metal directly deposited on an n-doped semiconductor structure, forming a Schottky barrier acting as a semi-selective contact for an electron temperature driven cell. Absorption of light is shown to be by free carrier absorption in the metal layer for illumination with wavelengths of light below the semiconductor band gap, giving rise to an IV characteristic with a reverse bias slope dependent on electron temperature. Illumination with light in excess of the band gap reveals a standard Schottky cell IV characteristic.
Boufflet P, Casey A, Xia Y, et 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.
Lin J, Liu B, Yu M, et al., 2016, Heteroatomic Conjugated Polymers and the Spectral Tuning of Electroluminescence via a Supramolecular Coordination Strategy, MACROMOLECULAR RAPID COMMUNICATIONS, Vol: 37, Pages: 1807-1813, ISSN: 1022-1336
Lin J-Y, Zhu G-Y, Liu B, et al., 2016, Supramolecular Polymer-Molecule Complexes as Gain Media for Ultraviolet Lasers, ACS MACRO LETTERS, Vol: 5, Pages: 967-971, ISSN: 2161-1653
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.
dimmock J, kauer M, Mellor AV, et al., 2016, Current Voltage Characteristics of a Metallic Structure for a Hot-Carrier Photovoltaic Cell, 43rd IEEE Photovoltaic Specialists Conference
Dimmock JAR, Kauer M, Smith K, et al., 2016, Optoelectronic characterization of carrier extraction in a hot carrier photovoltaic cell structure, Journal of Optics, Vol: 18, ISSN: 2040-8986
A hot carrier photovoltaic cell requires extraction of electrons on a timescale faster than they can lose energy to the lattice. We optically and optoelectronically characterize two resonant tunneling structures, showing their compatability with hot carrier photovoltaic operation, demonstrating structural and carrier extraction properties necessary for such a device. In particular we use time resolved and temperature dependent photoluminescence to determine extraction timescales and energy levels in the structures and demonstrate fast carrier extraction by tunneling. We also show that such devices are capable of extracting photo-generated electrons at high carrier densities, with an open circuit voltage in excess of 1 V.
Shaw JE, Perumal A, Bradley DDC, et al., 2016, Nanoscale current spreading analysis in solution-processed graphene oxide/silver nanowire transparent electrodes via conductive atomic force microscopy, Journal of Applied Physics, Vol: 119, ISSN: 1089-7550
Bradley DDC, Stavrinou PN, Perevedentsev A, et al., 2015, Solution-crystallization and related phenomena in 9,9-dialkyl-fluorene polymers. I. Crystalline polymer-solvent compound formation for poly(9,9-dioctylfluorene), Journal of Polymer Science, Polymer Physics Edition, Vol: 53, Pages: 1481-1491, ISSN: 0098-1273
Polymer-solvent compound formation, occurring via co-crystallization of polymer chains and selected small-molecular species, is demonstrated for the conjugated polymer poly(9,9-dioctylfluorene) (PFO) and a range of organic solvents. The resulting crystallization and gelation processes in PFO solutions are studied by differential scanning calorimetry, with X-ray diffraction providing additional information on the resulting microstructure. It is shown that PFO-solvent compounds comprise an ultra-regular molecular-level arrangement of the semiconducting polymer host and small-molecular solvent guest. Crystals form following adoption of the planar-zigzag β-phase chain conformation, which, due to its geometry, creates periodic cavities that accommodate the ordered inclusion of solvent molecules of matching volume. The findings are formalized in terms of nonequilibrium temperature–composition phase diagrams. The potential applications of these compounds and the new functionalities that they might enable are also discussed.
Bradley DDC, Perevedentsev A, Stavrinou PN, 2015, Solution-Crystallization and Related Phenomena in 9,9-Dialkyl-FluorenePolymers. II. Influence of Side-Chain Structure, Journal of Polymer Science, Polymer Physics Edition, Vol: 53, Pages: 1492-1506, ISSN: 0098-1273
Solution-crystallization is studied for two polyfluorene polymers possessing different side-chain structures. Thermal analysis and temperature-dependent optical spectroscopy are used to clarify the nature of the crystallization process, while X-ray diffraction and scanning electron microscopy reveal important differences in the resulting microstructures. It is shown that the planar-zigzag chain conformation termed the β-phase, which is observed for certain linear-side-chain polyfluorenes, is necessary for the formation of so-called polymer-solvent compounds for these polymers. Introduction of alternating fluorene repeat units with branched side-chains prevents formation of the β-phase conformation and results in non-solvated, i.e. melt-crystallization-type, polymer crystals. Unlike non-solvated polymer crystals, for which the chain conformation is stabilized by its incorporation into a crystalline lattice, the β-phase conformation is stabilized by complexation with solvent molecules and, therefore, its formation does not require specific inter-chain interactions. The presented results clarify the fundamental differences between the β-phase and other conformational/crystalline forms of polyfluorenes.
Fisher M, Farrell D, Zanella M, et al., 2015, Utilizing vertically aligned CdSe/CdS nanorods within a luminescent solar concentrator, APPLIED PHYSICS LETTERS, Vol: 106, ISSN: 0003-6951
Perevedentsev A, Sonnefraud Y, Belton CR, et al., 2015, Dip-pen patterning of poly(9,9-dioctylfluorene) chain-conformation-based nano-photonic elements, Nature Communications, Vol: 6, Pages: 1-9, ISSN: 2041-1723
Metamaterials are a promising new class of materials, in which sub-wavelength physical structures, rather than variations in chemical composition, can be used to modify the nature of their interaction with electromagnetic radiation. Here we show that a metamaterials approach, using a discrete physical geometry (conformation) of the segments of a polymer chain as the vector for a substantial refractive index change, can be used to enable visible wavelength, conjugated polymer photonic elements. In particular, we demonstrate that a novel form of dip-pen nanolithography provides an effective means to pattern the so-called β-phase conformation in poly(9,9-dioctylfluorene) thin films. This can be done on length scales ≤500 nm, as required to fabricate a variety of such elements, two of which are theoretically modelled using complex photonic dispersion calculations.
Walters RJ, Yoon W, Placencia D, et al., 2015, Multijunction Organic Photovoltaic Cells for Underwater Solar Power, IEEE 42nd Photovoltaic Specialist Conference (PVSC), Publisher: IEEE, ISSN: 0160-8371
Dimmock JAR, Kauer M, Stavrinou PN, et al., 2015, A metallic hot carrier photovoltaic cell, Conference on Physics, Simulation, and Photonic Engineering of Photovoltaic Devices IV, Publisher: SPIE-INT SOC OPTICAL ENGINEERING, ISSN: 0277-786X
Perumal A, Faber H, Yaacobi-Gross N, et al., 2015, High-Efficiency, Solution-Processed, Multilayer Phosphorescent Organic Light-Emitting Diodes with a Copper Thiocyanate Hole-Injection/Hole-Transport Layer, ADVANCED MATERIALS, Vol: 27, Pages: 93-100, ISSN: 0935-9648
Perevedentsev A, Aksel S, Feldman K, et al., 2015, Interplay Between Solid State Microstructure and Photophysics for Poly(9,9-dioctylfluorene) within Oriented Polyethylene Hosts, JOURNAL OF POLYMER SCIENCE PART B-POLYMER PHYSICS, Vol: 53, Pages: 22-38, ISSN: 0887-6266
Yaacobi-Gross N, Treat ND, Pattanasattayavong P, et al., 2014, High-Efficiency Organic Photovoltaic Cells Based on the Solution-Processable Hole Transporting Interlayer Copper Thiocyanate (CuSCN) as a Replacement for PEDOT:PSS, Advanced Energy Materials, Vol: 5, ISSN: 1614-6840
The use of copper thiocyanate (CuSCN) as a universal solution-processable and highly transparent hole-transporting layer in organic bulk-heterojunction photovoltaic cells is demonstrated. When CuSCN is employed as a replacement for the commonly used poly(3,4-ethylenedioxythiophene):polystyrenesulfonate (PEDOT:PSS), organic solar cells with maximum power conversion efficiency of 8%, are realized; this value is 1.27 times higher than that for optimized control cells based on PEDOT:PSS.
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