122 results found
Matarese BFE, Feyen PLC, Falco A, et al., 2018, Use of SU8 as a stable and biocompatible adhesion layer for gold bioelectrodes, Scientific Reports, Vol: 8, ISSN: 2045-2322
Gold is the most widely used electrode material for bioelectronic applications due to its high electrical conductivity,good chemical stability and proven biocompatibility. However, gold adheres only weakly to widely used substratematerials such as glass and silicon oxide, typically requiring the use of a thin layer of chromium between thesubstrate and the metal to achieve adequate adhesion. Unfortunately, this approach can reduce biocompatibilityrelative to pure gold films due to the risk of the underlying layer of chromium becoming exposed. Here we report onan alternative adhesion layer for gold and other metals formed from a thin layer of the negative-tone photoresist SU8,which we find to be significantly less cytotoxic than chromium, being broadly comparable to bare glass in terms ofits biocompatibility. Various treatment protocols for SU-8 were investigated, with a view to attaining hightransparency and good mechanical and biochemical stability. Thermal annealing to induce partial cross-linking of theSU-8 film prior to gold deposition, with further annealing after deposition to complete cross-linking, was found toyield the best electrode properties. The optimized glass/SU8-Au electrodes were highly transparent, resilient todelamination, stable in biological culture medium, and exhibited similar biocompatibility to glass.
Walker BE, Bannock JH, Nightingale AM, et al., 2017, Tuning reaction products by constrained optimisation, Reaction Chemistry and Engineering, Vol: 2, Pages: 785-798, ISSN: 2058-9883
We describe an effective means of defining optimisation criteria for self-optimising reactors, applicable to situations where a compromise is sought between several competing objectives. The problem is framed as a constrained optimisation, in which a lead property is optimised subject to constraints on the values that other properties may assume. Compared to conventional methods (using weighted-sum- and weighted-product-based merit functions), the approach described here is more intuitive, easier to implement, and yields an optimised solution that more faithfully reflects user preferences. The method is applied here to the synthesis of o-xylenyl adducts of Buckminsterfullerene, using a cascadic reaction of the form X0 → X1 → X2 → … XN. Specifically, we selectively target the formation of the (technologically useful) first- and second-order adducts X1 and X2, while at the same time suppressing the formation of unwanted higher-order products. More generally, the approach is applicable to any chemical optimisation involving a trade-off between competing criteria. To assist with implementation we provide a self-contained software package for carrying out constrained optimisation, together with detailed tutorial-style instructions.
Abelha TF, Phillips TW, Bannock JH, et al., 2017, Bright conjugated polymer nanoparticles containing a biodegradable shell produced at high yields and with tuneable optical properties by a scalable microfluidic device, NANOSCALE, Vol: 9, Pages: 2009-2019, ISSN: 2040-3364
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 (PCBM, bisPCBM, and 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
Nightingale AM, deMello JC, 2016, Improving the ensemble optical properties of InP quantum dots by indium precursor modification, Journal of Materials Chemistry C, Vol: 4, Pages: 8454-8458, ISSN: 2050-7526
Indium phosphide quantum dots typically exhibit broad and poorly defined ensemble optical properties due to a highly pronounced nucleation period that consumes virtually all phosphorus precursors, leading to subsequent growth by Ostwald ripening and poor final size distributions. Previous attempts to reduce the reactivity of the phosphorus precursor, and thereby limit its consumption during the nucleation phase, have not led to appreciably better optical properties due to an unwanted increase in the duration of nucleation. Here we present an alternative approach to reducing initial precursor consumption using a simple modification of the indium precursor, in which the widely used carboxylate ligand is replaced by a phosphine. The change of ligand leaves residual precursor available for size-focusing growth after nucleation, leading to significantly improved spectral features. Band-edge emission peaks are typically 30% narrower than for the standard method.
Bannock JH, Xu W, Baïssas T, et 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.
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.
Falco A, Matarese B, Feyen P, et al., 2016, Investigation of the Stability and Biocompatibility of Commonly Used Electrode Materials in Organic Neurooptoelectronics, IEEE TRANSACTIONS ON NANOTECHNOLOGY, Vol: 15, Pages: 746-753, ISSN: 1536-125X
Matarese BFE, 2015, Investigation of the stability and biocompatibility of commonly used electrode materials in organic neuro-optoelectronics, Nanotechnology (IEEE-NANO) , 2015 IEEE 15th International Conference on, Publisher: IEEE, Pages: 1539-1542
We have investigated the stability of key electro-optical properties (Conductivity, Work Function, Transmittance) of several commonly used electrode materials for organic optoelectronics (Indium-Tin Oxide, Gold, Silver, Aluminum) in different media (Air, DI water, Phosphate Buffered Saline and Dulbecco's Modified Eagle Medium). By comparing the electrode materials side by side, we aimed to identify their advantages and drawbacks for use in solid/liquid devices. Since many applications of such devices involve the direct contact with biological species, we also investigated their biocompatibility by evaluating cytotoxicity of HEK293 cells cultured on the candidate materials.
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.
Phillips T, Bannock JH, de Mello JC, 2015, Microscale extraction and phase separation using a porous capillary, Lab on a Chip, Vol: 15, Pages: 2960-2967, ISSN: 1473-0197
We report the use of a porous polytetrafluoroethylene capillary for the inline separation of liquid–liquid segmented flows, based on the selective wetting and permeation of the porous capillary walls by one of the liquids. Insertion of a narrow flow restriction at the capillary outlet allows the back pressure to be tuned for multiple liquid–liquid combinations and flow conditions. In this way, efficient separation of aqueous–organic, aqueous–fluorous and organic–fluorous segmented flows can be readily achieved over a wide range of flow rates. The porous-capillary-separator enables the straightforward regeneration of a continuous flow from a segmented flow, and may be applied to various applications, including inline analysis, biphasic reactions, and purification. As a demonstration of the latter, we performed a simple inline aqueous–organic extraction of the pH indicator 2,6-dichloroindophenol. An aqueous solution of the conjugate base was mixed with hydrochloric acid in continuous flow to protonate the indicator and render it organic-soluble. The indicator was then extracted from the aqueous feed into chloroform using a segmented flow. The two liquids were finally separated inline using a porous PTFE capillary, with the aqueous phase emerging as a continuous stream from the separator outlet. UV-visible absorption spectroscopy showed the concentration of indicator in the outflowing aqueous phase to be less than one percent of its original value, confirming the efficacy of the extraction and separation process.
Buchaca-Domingo E, Vandewal K, Fei Z, et 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
Here we show that the charge transfer (CT) absorption signal in bulk-heterojunction solar cell blends, measured by photothermal deflection spectroscopy, is directly proportional to the density of molecular donor:acceptor interfaces. Since the optical transitions from the ground state to the interfacial CT state are weakly allowed at photon energies below the optical gap of both the donor and acceptor, we can exploit the use of this sensitive linear absorption spectroscopy for such quantification. Moreover, we determine the absolute molar extinction coefficient of the CT transition for an archetypical polymer:fullerene interface. The latter is ∼100 times lower than the extinction coefficient of the donor chromophore involved, allowing us to experimentally estimate the transition dipole moment as 0.3 D and the electronic coupling between the ground and CT states to be on the order of 30 meV.
de Mello J, Anthony J, Lee S, 2015, Organic electronics: recent developments., Chemphyschem, Vol: 16, Pages: 1099-1100
Pang C, Chellappan V, Yim JH, et al., 2015, Enhanced Performance Using an SU-8 Dielectric Inter layer in a Bulk Heterojunction Organic Solar Cell, ACS APPLIED MATERIALS & INTERFACES, Vol: 7, Pages: 5219-5225, ISSN: 1944-8244
Hellmann C, Treat ND, Scaccabarozzi AD, et al., 2015, Solution Processing of Polymer Semiconductor: Insulator Blends-Tailored Optical Properties Through Liquid-Liquid Phase Separation Control, JOURNAL OF POLYMER SCIENCE PART B-POLYMER PHYSICS, Vol: 53, Pages: 304-310, ISSN: 0887-6266
Dattani R, Telling MTF, Lopez CG, et al., 2015, Rapid precipitation: An alternative to solvent casting for organic solar cells, Chemphyschem, Vol: 16, Pages: 1231-1238, ISSN: 1439-7641
Rapid precipitation, immersion of a liquid formulation into a nonsolvent, is compared with drop casting for fabricating organic solar cells. Blends comprising poly-3-hexylthiophene (P3HT), phenyl-C61-butyric acid methyl ester (PCBM), and chlorobenzene were processed into bulk samples by using two distinct routes: rapid precipitation and drop casting. The resulting structure, phases, and crystallinity were analyzed by using small-angle neutron scattering, X-ray diffraction, differential scanning calorimetry, and muon spin resonance. Rapid precipitation was found to induce a finely structured phase separation between PCBM and P3HT, with 65 wt % crystallinity in the P3HT phase. In contrast, solvent casting resulted in a mixed PCBM/P3HT phase with only 43 wt % P3HT crystallinity. The structural advantages conferred by rapid precipitation were shown to persist following intense thermal treatments.
Edwards AN, Yamazaki M, Krishnadasan SH, et al., 2015, Photostable phosphorescent polymer nanospheres for high sensitivity detection, JOURNAL OF MATERIALS CHEMISTRY C, Vol: 3, Pages: 6565-6572, ISSN: 2050-7526
Dattani R, Bannock JH, Fei Z, et al., 2014, A general mechanism for controlling thin film structures in all-conjugated block copolymer: fullerene blends, JOURNAL OF MATERIALS CHEMISTRY A, Vol: 2, Pages: 14711-14719, ISSN: 2050-7488
Bannock JH, Krishnadasan SH, Heeney M, et al., 2014, A gentle introduction to the noble art of flow chemistry, MATERIALS HORIZONS, Vol: 1, Pages: 373-378, ISSN: 2051-6347
Phillips TW, Lignos IG, Maceiczyk RM, et al., 2014, Nanocrystal synthesis in microfluidic reactors: where next?, Lab on a Chip
Nightingale AM, Phillips TW, Bannock JH, et al., 2014, Controlled multistep synthesis in a three-phase droplet reactor, Nature Communications, Vol: 5, Pages: 1-8, ISSN: 2041-1723
Channel-fouling is a pervasive problem in continuous flow chemistry, causing poor productcontrol and reactor failure. Droplet chemistry, in which the reaction mixture flows as discretedroplets inside an immiscible carrier liquid, prevents fouling by isolating the reaction from thechannel walls. Unfortunately, the difficulty of controllably adding new reagents to an existingdroplet stream has largely restricted droplet chemistry to simple reactions in which allreagents are supplied at the time of droplet formation. Here we describe an effective methodfor repeatedly adding controlled quantities of reagents to droplets. The reagents are injectedinto a multiphase fluid stream, comprising the carrier liquid, droplets of the reaction mixtureand an inert gas that maintains a uniform droplet spacing and suppresses new dropletformation. The method, which is suited to many multistep reactions, is applied to a five-stagequantum dot synthesis wherein particle growth is sustained by repeatedly adding freshfeedstock.
Georgiev YM, Petkov N, McCarthy B, et al., 2014, Fully CMOS-compatible top-down fabrication of sub-50 nm silicon nanowire sensing devices, MICROELECTRONIC ENGINEERING, Vol: 118, Pages: 47-53, ISSN: 0167-9317
Phillips TW, 2014, Flow synthesis of silver nanowires for low cost and high performance transparent conducting electrodes, Materials Research Society Spring 2014
Fagas G, Nolan M, Georgiev YM, et al., 2014, Component design and testing for a miniaturised autonomous sensor based on a nanowire materials platform, Conference on Smart Sensors, Actuators and MEMS within the SPIE EUROPE Symposium on Microtechnologies, Publisher: SPRINGER HEIDELBERG, Pages: 971-988, ISSN: 0946-7076
Yim JH, Joe S-Y, Pang C, et al., 2014, Fully Solution-Processed Semitransparent Organic Solar Cells with a Silver Nanowire Cathode and a Conducting Polymer Anode, ACS Nano, Vol: 8, Pages: 2857-2863, ISSN: 1936-0851
We report the fabrication of efficient indium tin oxide-free organicsolar cells based on poly(3-hexylthiophene-2,5-diyl):[6,6]-phenyl-C61-butyric acid methylester (P3HT:PCBM). All layers of the devices from the lowermost silver nanowire cathodeto the uppermost conducting polymer anode are deposited from solution and processedat plastic-compatible temperatures <200 C. Owing to the absence of an opaque metalelectrode, the devices are semitransparent with potential applications in powergeneratingwindows and tandem-cells. The measured power conversion efficiencies(PCEs) of 2.3 and 2.0% under cathode- and anode-side illumination, respectively, matchpreviously reported PCE values for equivalent semitransparent organic solar cells usingindium tin oxide.
Bannock JH, Al-Hashimi M, Krishnadasan SH, et al., 2014, Controlled synthesis of conjugated random copolymers in a droplet-based microreactor, Materials Horizons
Beesley DJ, Semple J, Krishnan Jagadamma L, et al., 2014, Sub-15-nm patterning of asymmetric metal electrodes and devices by adhesion lithography, Nat Commun, Vol: 5
Coplanar electrodes formed from asymmetric metals separated on the nanometre length scale are essential elements of nanoscale photonic and electronic devices. Existing fabrication methods typically involve electron-beam lithography—a technique that enables high fidelity patterning but suffers from significant limitations in terms of low throughput, poor scalability to large areas and restrictive choice of substrate and electrode materials. Here, we describe a versatile method for the rapid fabrication of asymmetric nanogap electrodes that exploits the ability of selected self-assembled monolayers to attach conformally to a prepatterned metal layer and thereby weaken adhesion to a subsequently deposited metal film. The method may be carried out under ambient conditions using simple equipment and a minimum of processing steps, enabling the rapid fabrication of nanogap electrodes and optoelectronic devices with aspect ratios in excess of 100,000.
Khan FR, Schmuecking K, Krishnadasan SH, et al., 2013, DIETARY BIOAVAILABILITY OF CADMIUM PRESENTED TO THE GASTROPOD PERINGIA ULVAE AS QUANTUM DOTS AND IN IONIC FORM, ENVIRONMENTAL TOXICOLOGY AND CHEMISTRY, Vol: 32, Pages: 2621-2629, ISSN: 0730-7268
Xia R, Leem D-S, Kirchartz T, et al., 2013, Investigation of a Conjugated Polyelectrolyte Interlayer for Inverted Polymer:Fullerene Solar Cells, ADVANCED ENERGY MATERIALS, Vol: 3, Pages: 718-723, ISSN: 1614-6832
Nightingale AM, deMello JC, 2013, Segmented Flow Reactors for Nanocrystal Synthesis, ADVANCED MATERIALS, Vol: 25, Pages: 1813-1821, ISSN: 0935-9648
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