34 results found
Karim MMS, Ganose AM, Pieters L, et al., 2019, Anion Distribution, Structural Distortion, and Symmetry-Driven Optical Band Gap Bowing in Mixed Halide Cs2SnX6 Vacancy Ordered Double Perovskites, CHEMISTRY OF MATERIALS, Vol: 31, Pages: 9430-9444, ISSN: 0897-4756
Yan H, Limbu S, Wang X, et al., 2019, Efficient charge carrier injection and balance achieved by low electrochemical doping in solution-processed polymer light-emitting diodes, Advanced Functional Materials, Vol: 29, Pages: 1-9, ISSN: 1616-301X
Charge carrier injection and transport in polymer light‐emitting diodes (PLEDs) is strongly limited by the energy level offset at organic/(in)organic interfaces and the mismatch in electron and hole mobilities. Herein, these limitations are overcome via electrochemical doping of a light‐emitting polymer. Less than 1 wt% of doping agent is enough to effectively tune charge injection and balance and hence significantly improve PLED performance. For thick single‐layer (1.2 µm) PLEDs, dramatic reductions in current and luminance turn‐on voltages (VJ = 11.6 V from 20.0 V and VL = 12.7 V from 19.8 V with/without doping) accompanied by reduced efficiency roll‐off are observed. For thinner (<100 nm) PLEDs, electrochemical doping removes a thickness dependence on VJ and VL, enabling homogeneous electroluminescence emission in large‐area doped devices. Such efficient charge injection and balance properties achieved in doped PLEDs are attributed to a strong electrochemical interaction between the polymer and the doping agents, which is probed by in situ electric‐field‐dependent Raman spectroscopy combined with further electrical and energetic analysis. This approach to control charge injection and balance in solution‐processed PLEDs by low electrochemical doping provides a simple yet feasible strategy for developing high‐quality and efficient lighting applications that are fully compatible with printing technologies.
Wade J, Pugh H, Nightingale J, et al., 2019, Colour in bivalve shells: Using resonance Raman spectroscopy to compare pigments at different phylogenetic levels, Journal of Raman Spectroscopy, Vol: 50, Pages: 1527-1536, ISSN: 0377-0486
Several studies have suggested that shell colour may be phylogenetically distributed within the phylum Mollusca, but this pattern is confounded by our ignorance of the homology of colour and lack of understanding about the identity of most molluscan pigments. We use resonance Raman spectroscopy to address this problem by examining bivalve pigments producing a range of colours and compare spectra from taxa at different phylogenetic levels. The spectra of most shell pigments exhibited a skeletal signature typical of partially methylated polyenes, possibly modified carotenoids, with the strongest peaks occurring between 1,501–1,540 cm−1 and 1,117–1,144 cm−1 due to the C═C (ν1) and C–C (ν2) stretching modes, respectively. Neither pigment class nor mineral structure differentiated Imparidentia and Pteriomorphia. Spectral acquisitions for purple pigments for two species of Asaphis suggest that identical or nearly identical pigments are shared within this genus, and some red pigments from distantly related species have similar spectra. Conversely, two species with brown shells have distinctly different pigments, highlighting the difficulty in determining the homology of colour even within a single class of pigments. Curiously, we were unable to detect any Raman activity for green‐coloured shell or pigment peaks for the yellow area of Codakia paytenorum, suggesting that these colours are due to structural elements or a pigment that is quite different from those observed in other taxa examined to date. Our results are consistent with the idea that classes of pigments are evolutionarily ancient but heritable modifications may be specific to clades.
Britton B, Jackson C, Wade J, 2019, The reward and risk of social media for academics, Nature Reviews Chemistry, Vol: 3, Pages: 459-461, ISSN: 2397-3358
We are three academics who are active on social media. We explore the motivations for and benefits of engaging with social media, as well as its costs and risks. Overall, we believe this engagement to be a net benefit for us, our employers and for wider society.
Wan L, Wade J, Salerno F, et al., 2019, Inverting the handedness of circularly polarized luminescence from light-emitting polymers using film thickness, ACS Nano, Vol: 13, Pages: 8099-8105, ISSN: 1936-0851
The emission of circularly polarized light is central to many applications, including data storage, optical quantum computation, biosensing, environmental monitoring, and display technologies. An emerging method to induce (chiral) circularly polarized (CP) electroluminescence from the active layer of polymer light-emitting diodes (polymer OLEDs; PLEDs) involves blending achiral polymers with chiral small-molecule additives, where the handedness/sign of the CP light is controlled by the absolute stereochemistry of the small molecule. Through the in-depth study of such a system we report an interesting chiroptical property: the ability to tune the sign of CP light as a function of active layer thickness for a fixed enantiomer of the chiral additive. We demonstrate that it is possible to achieve both efficient (4.0 cd/A) and bright (8000 cd/m2) CP-PLEDs, with high dissymmetry of emission of both left-handed (LH) and right-handed (RH) light, depending on thickness (thin films, 110 nm: gEL = 0.51, thick films, 160 nm: gEL = -1.05, with the terms "thick" and "thin" representing the upper and lower limits of the thickness regime studied), for the same additive enantiomer. We propose that this arises due to an interplay between localized CP emission originating from molecular chirality and CP light amplification or inversion through a chiral medium. We link morphological, spectroscopic, and electronic characterization in thin films and devices with theoretical studies in an effort to determine the factors that underpin these observations. Through the control of active layer thickness and device architecture, this study provides insights into the mechanisms that result in CP luminescence and high performance from CP-PLEDs, as well as demonstrating new opportunities in CP photonic device design.
Wade J, 2019, 30 years of the Web, PHYSICS WORLD, Vol: 32, Pages: 38-38, ISSN: 0953-8585
Wade J, 2019, Let's fight sexism with data, NEW SCIENTIST, Vol: 241, Pages: 24-25, ISSN: 0262-4079
Gabrys BJ, Wade J, Dyer J, et al., 2019, Women in Physics in the UK: On the Road to Equality, 6th IUPAP International Conference on Women in Physics (ICWIP), Publisher: AMER INST PHYSICS, ISSN: 0094-243X
Meza-Montes L, Betacchy M, Hodari A, et al., 2019, Workshop Report: Cultural Bias and Perception, 6th IUPAP International Conference on Women in Physics (ICWIP), Publisher: AMER INST PHYSICS, ISSN: 0094-243X
Wade J, Zaringhalam M, 2019, Why we need to keep talking about equality in physics, Physics World, Vol: 32, Pages: 34-38, ISSN: 0953-8585
Nightingale J, Wade J, Moia D, et al., 2018, Impact of molecular order on polaron formation in conjugated polymers, The Journal of Physical Chemistry C, Vol: 122, Pages: 29129-29140, ISSN: 1932-7447
The nature of polaron formation has profound implications on the transport of charge carriers in conjugated polymers, but still remains poorly understood. Here we develop in situ electrochemical resonant Raman spectroscopy, a powerful structural probe that allows direct observation of polaron formation. We report that polaron formation in ordered poly(3-hexyl)thiophene (P3HT) polymer domains (crystalline phase) results in less pronounced changes in molecular conformation, indicating smaller lattice relaxation, compared to polarons generated in disordered polymer domains (amorphous phase) for which we observe large molecular conformational changes. These conformational changes are directly related to the effective conjugation length of the polymer. Furthermore, we elucidate how blending the P3HT polymer with phenyl C-61 butyric acid methyl ester (PCBM) affects polaron formation in the polymer. We find that blending disturbs polymer crystallinity, reducing the density of polarons that can form upon charge injection at the same potential, whilst the lost capacity is partly restored during post-deposition thermal annealing. Our study provides direct spectroscopic evidence for a lower degree of lattice reorganisation in crystalline (and therefore more planarised) polymers than in conformationally disordered polymers. This observation is consistent with higher charge carrier mobility and better device performance commonly found in crystalline polymer materials.
Wade J, Wood S, 2018, Materials for the 21st century, Europhysics News, Vol: 49, Pages: 14-17, ISSN: 0531-7479
Wade J, 2018, Balance the equation, NEW SCIENTIST, Vol: 240, Pages: 26-27, ISSN: 0262-4079
Wade J, 2018, Making health digital, PHYSICS WORLD, Vol: 31, Pages: 27-30, ISSN: 0953-8585
Wade J, 2018, Rooted in physics, PHYSICS WORLD, Vol: 31, Pages: 38-41, ISSN: 0953-8585
Wade J, Wood S, Collado-Fregoso E, et al., 2017, Impact of Fullerene Intercalation on Structural and Thermal Properties of Organic Photovoltaic Blends, JOURNAL OF PHYSICAL CHEMISTRY C, Vol: 121, Pages: 20976-20985, ISSN: 1932-7447
The performance of organic photovoltaic blend devices is critically dependent on the polymer:fullerene interface. These interfaces are expected to impact the structural and thermal properties of the polymer with regards to the conjugated backbone planarity and transition temperatures during annealing/cooling processes. Here, we report the impact of fullerene intercalation on structural and thermal properties of poly(2,5-bis(3-tetradecylthiophen-2-yl)thieno[3,2-b]thiophene (PBTTT), a highly stable material known to exhibit liquid crystalline behavior. We undertake a detailed systematic study of the extent of intercalation in the PBTTT:fullerene blend, considering the use of four different fullerene derivatives and also varying the loading ratios. Resonant Raman spectroscopy allows direct observation of the interface morphology in situ during controlled heating and cooling. We find that small fullerene molecules readily intercalate into PBTTT crystallites, resulting in a planarization of the polymer backbone, but high fullerene loading ratios or larger fullerenes result in nonintercalated domains. During cooling from melt, nonintercalated blend films are found to return to their original morphology and reproduce all thermal transitions on cooling with minimal hysteresis. Intercalated blend films show significant hysteresis on cooling due to the crystallized fullerene attempting to reintercalate. The strongest hysteresis is for intercalated blend films with excess fullerene loading ratio, which form a distinct nanoribbon morphology and exhibit a reduced geminate recombination rate. These results reveal that careful consideration should be taken during device fabrication, as postdeposition thermal treatments significantly impact the charge generation and recombination dynamics.
Tesh S, Wade J, 2017, 'Look happy dear, you've just made a discovery', PHYSICS WORLD, Vol: 30, Pages: 31-33, ISSN: 0953-8585
Boufflet P, Wood S, Wade J, et 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.
Fernando B, Wade J, Tazi K, 2016, Sowing seeds from space, Astronomy and Geophysics, Vol: 57, ISSN: 1366-8781
Fernando B, Wade J, Tazi K, 2016, Sowing seeds from space, ASTRONOMY & GEOPHYSICS, Vol: 57, Pages: 11-11, ISSN: 1366-8781
Wood S, Kim J-H, Wade J, et al., 2016, Systematic control of heteroatoms in donor-acceptor copolymers and its effects on molecular conformation and photovoltaic performance, JOURNAL OF MATERIALS CHEMISTRY C, Vol: 4, Pages: 7966-7978, ISSN: 2050-7526
Kim J-H, Wood S, Park JB, et al., 2016, Optimization and Analysis of Conjugated Polymer Side Chains for High-Performance Organic Photovoltaic Cells, ADVANCED FUNCTIONAL MATERIALS, Vol: 26, Pages: 1517-1525, ISSN: 1616-301X
Kang C-M, Wade J, Yun S, et al., 2016, 1 GHz Pentacene Diode Rectifiers Enabled by Controlled Film Deposition on SAM-Treated Au Anodes, ADVANCED ELECTRONIC MATERIALS, Vol: 2, ISSN: 2199-160X
Wade J, Wood S, Beatrup D, et al., 2015, Operational electrochemical stability of thiophene-thiazole copolymers probed by resonant Raman spectroscopy., Journal of Chemical Physics, Vol: 142, Pages: 244904-244904, ISSN: 1089-7690
We report on the electrochemical stability of hole polarons in three conjugated polymers probed by resonant Raman spectroscopy. The materials considered are all isostructural to poly(3-hexyl)thiophene, where thiazole units have been included to systematically deepen the energy level of the highest occupied molecular orbital (HOMO). We demonstrate that increasing the thiazole content planarizes the main conjugated backbone of the polymer and improves the electrochemical stability in the ground state. However, these more planar thiazole containing polymers are increasingly susceptible to electrochemical degradation in the polaronic excited state. We identify the degradation mechanism, which targets the C=N bond in the thiazole units and results in disruption of the main polymer backbone conjugation. The introduction of thiazole units to deepen the HOMO energy level and increase the conjugated backbone planarity can be beneficial for the performance of certain optoelectronic devices, but the reduced electrochemical stability of the hole polaron may compromise their operational stability.
Fei Z, Boufflet P, Wood S, et 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.
Higgins SG, Muir BVO, Wade J, et al., 2015, Self-aligned megahertz organic transistors solution-processed on plastic, Advanced Electronic Materials, Vol: 1, ISSN: 2199-160X
Higgins SG, Muir BVO, Wade J, et al., 2015, Organic Transistors: Self-Aligned Megahertz Organic Transistors Solution-Processed on Plastic (Adv. Electron. Mater. 5/2015), Advanced Electronic Materials, Vol: 1
Wood S, Wade J, Shahid M, et al., 2015, Natures of optical absorption transitions and excitation energy dependent photostability of diketopyrrolopyrrole (DPP)-based photovoltaic copolymers, ENERGY & ENVIRONMENTAL SCIENCE, Vol: 8, Pages: 3222-3232, ISSN: 1754-5692
Wade J, Steiner F, Niedzialek D, et al., 2014, Charge mobility anisotropy of functionalized pentacenes in organic field effect transistors fabricated by solution processing, JOURNAL OF MATERIALS CHEMISTRY C, Vol: 2, Pages: 10110-10115, ISSN: 2050-7526
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