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  • Journal article
    Wade J, Wood S, Beatrup D, Hurhangee M, Bronstein H, McCulloch I, Durrant JR, Kim JSet 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.
  • Journal article
    Reynal A, Pastor E, Gross MA, Selim S, Reisner E, Durrant JRet al., 2015,

    Unravelling the pH-dependence of a molecular photocatalytic system for hydrogen production

    , Chemical Science, Vol: 6, Pages: 4855-4859, ISSN: 2041-6539

    Photocatalytic systems for the reduction of aqueous protons are strongly pH-dependent, but the origin of this dependency is still not fully understood. We have studied the effect of different degrees of acidity on the electron transfer dynamics and catalysis taking place in a homogeneous photocatalytic system composed of a phosphonated ruthenium tris(bipyridine) dye (RuP) and a nickel bis(diphosphine) electrocatalyst (NiP) in an aqueous ascorbic acid solution. Our approach is based on transient absorption spectroscopy studies of the efficiency of photo-reduction of RuP and NiP correlated with pH-dependent photocatalytic H2 production and the degree of catalyst protonation. The influence of these factors results in an observed optimum photoactivity at pH 4.5 for the RuP–NiP system. The electron transfer from photo-reduced RuP to NiP is efficient and independent of the pH value of the medium. At pH <4.5, the efficiency of the system is limited by the yield of RuP photo-reduction by the sacrificial electron donor, ascorbic acid. At pH >4.5, the efficiency of the system is limited by the poor protonation of NiP, which inhibits its ability to reduce protons to hydrogen. We have therefore developed a rational strategy utilising transient absorption spectroscopy combined with bulk pH titration, electrocatalytic and photocatalytic experiments to disentangle the complex pH-dependent activity of the homogenous RuP–NiP photocatalytic system, which can be widely applied to other photocatalytic systems.
  • Journal article
    Le Formal F, Pastor E, Tilley SD, Mesa CA, Pendlebury SR, Graetzel M, Durrant JRet al., 2015,

    Rate law analysis of water oxidation on a hematite surface

    , Journal of the American Chemical Society, Vol: 137, Pages: 6629-6637, ISSN: 1520-5126

    Water oxidation is a key chemical reaction, central to both biological photosynthesis and artificial solar fuel synthesis strategies. Despite recent progress on the structure of the natural catalytic site, and on inorganic catalyst function, determining the mechanistic details of this multiredox reaction remains a significant challenge. We report herein a rate law analysis of the order of water oxidation as a function of surface hole density on a hematite photoanode employing photoinduced absorption spectroscopy. Our study reveals a transition from a slow, first order reaction at low accumulated hole density to a faster, third order mechanism once the surface hole density is sufficient to enable the oxidation of nearest neighbor metal atoms. This study thus provides direct evidence for the multihole catalysis of water oxidation by hematite, and demonstrates the hole accumulation level required to achieve this, leading to key insights both for reaction mechanism and strategies to enhance function.
  • Journal article
    Wang X, Kafizas A, Li X, Moniz SJA, Reardon PJT, Tang J, Parkin IP, Durrant JRet al., 2015,

    Transient Absorption Spectroscopy of Anatase and Rutile: The Impact of Morphology and Phase on Photocatalytic Activity

    , JOURNAL OF PHYSICAL CHEMISTRY C, Vol: 119, Pages: 10439-10447, ISSN: 1932-7447
  • Journal article
    Kafizas AG, Durrant JR,

    Transient Absorption Spectroscopy of Anatase and Rutile: the Impact of Morphology and Phase on Photocatalytic Activity

    , The Journal of Physical Chemistry C, ISSN: 1932-7447
  • Journal article
    Sotelo-Vazquez C, Noor N, Kafizas A, Quesada-Cabrera R, Scanlon DO, Taylor A, Durrant JR, Parkin IPet al., 2015,

    Multifunctional P-Doped TiO2 films: a new approach to self-cleaning, transparent conducting oxide materials

    , Chemistry of Materials, Vol: 27, Pages: 3234-3242, ISSN: 1520-5002

    Multifunctional P-doped TiO2 thin films were synthesized by atmospheric pressure chemical vapor deposition (APCVD). This is the first example of P-doped TiO2 films with both P5+ and P3– states, with the relative proportion being determined by synthesis conditions. This technique to control the oxidation state of the impurities presents a new approach to achieve films with both self-cleaning and TCO properties. The origin of electrical conductivity in these materials was correlated to the incorporation of P5+ species, as suggested by Hall Effect probe measurements. The photocatalytic performance of the films was investigated using the model organic pollutant, stearic acid, with films containing predominately P3– states found to be vastly inferior photocatalysts compared to undoped TiO2 films. Transient absorption spectroscopy studies also showed that charge carrier concentrations increased by several orders of magnitude in films containing P5+ species only, whereas photogenerated carrier lifetimes—and thus photocatalytic activity—were severely reduced upon incorporation of P3– species. The results presented here provide important insights on the influence of dopant nature and location within a semiconductor structure. These new P-doped TiO2 films are a breakthrough in the development of multifunctional advanced materials with tuned properties for a wide range of applications.
  • Journal article
    Deledalle F, Kirchartz T, Vezie MS, Campoy-Quiles M, Tuladhar PS, Nelson J, Durrant JRet al., 2015,

    Understanding the Effect of Unintentional Doping on Transport Optimization and Analysis in Efficient Organic Bulk-Heterojunction Solar Cells

    , PHYSICAL REVIEW X, Vol: 5, ISSN: 2160-3308
  • Journal article
    O'Mahony FTF, Lee YH, Jellett C, Dmitrov S, Bryant DTJ, Durrant JR, O'Regan BC, Graetzel M, Nazeeruddin MK, Haque SAet al., 2015,

    Improved environmental stability of organic lead trihalide perovskite-based photoactive-layers in the presence of mesoporous TiO2

    , Journal of Materials Chemistry A, Vol: 3, Pages: 7219-7223, ISSN: 2050-7496

    Impressive hybrid photovoltaic device performances have been realised with the methylammonium lead triiodide (MAPbI3) perovskite absorber in a wide range of device architectures. However, the question as to which of these systems represents the most commercially viable long-term prospect is yet to be answered conclusively. Here, we report on the photoinduced charge transfer processes in MAPbI3 based films measured under inert and ambient conditions. When exposed to ambient conditions, the coated mesoporous Al2O3 and bilayer systems show a rapid and significant degradation in the yield of long-lived charge separation. This process, which does not affect sensitized-mesoporous TiO2 films, is only found to occur when both light and oxygen are present. These observations indicate that the presence of a mesostructured TiO2 electron acceptor to rapidly extract the photoexcited electron from the perovskite sensitizer may be crucial for fundamental photovoltaic stability and significantly increases innate tolerance to environmental conditions. This work highlights a significant advantage of retaining mesoscale morphological control in the design of perovskite photovoltaics.
  • Journal article
    Dimitrov SD, Wheeler S, Niedzialek D, Schroeder BC, Utzat H, Frost JM, Yao J, Gillett A, Tuladhar PS, McCulloch I, Nelson J, Durrant JRet al., 2015,

    Polaron pair mediated triplet generation in polymer/fullerene blends

    , Nature Communications, Vol: 6, ISSN: 2041-1723

    Electron spin is a key consideration for the function of organic semiconductors in light-emitting diodes and solar cells, as well as spintronic applications relying on organic magnetoresistance. A mechanism for triplet excited state generation in such systems is by recombination of electron-hole pairs. However, the exact charge recombination mechanism, whether geminate or nongeminate and whether it involves spin-state mixing is not well understood. In this work, the dynamics of free charge separation competing with recombination to polymer triplet states is studied in two closely related polymer-fullerene blends with differing polymer fluorination and photovoltaic performance. Using time-resolved laser spectroscopic techniques and quantum chemical calculations, we show that lower charge separation in the fluorinated system is associated with the formation of bound electron-hole pairs, which undergo spin-state mixing on the nanosecond timescale and subsequent geminate recombination to triplet excitons. We find that these bound electron-hole pairs can be dissociated by electric fields.
  • Journal article
    Windle CD, Pastor E, Reynal A, Whitwood AC, Vaynzof Y, Durrant JR, Perutz RN, Reisner Eet al., 2015,

    Improving the Photocatalytic Reduction of CO2 to CO through Immobilisation of a Molecular Re Catalyst on TiO2

    , CHEMISTRY-A EUROPEAN JOURNAL, Vol: 21, Pages: 3746-3754, ISSN: 0947-6539
  • Journal article
    Holliday S, Ashraf RS, Nielsen CB, Kirkus M, Roehr JA, Tan C-H, Collado-Fregoso E, Knall A-C, Durrant JR, Nelson J, McCulloch Iet al., 2015,

    A rhodanine flanked nonfullerene acceptor for solution-processed organic photovoltaics

    , Journal of the American Chemical Society, Vol: 137, Pages: 898-904, ISSN: 0002-7863

    A novel small molecule, FBR, bearing 3-ethylrhodanine flanking groups was synthesized as a nonfullerene electron acceptor for solution-processed bulk heterojunction organic photovoltaics (OPV). A straightforward synthesis route was employed, offering the potential for large scale preparation of this material. Inverted OPV devices employing poly(3-hexylthiophene) (P3HT) as the donor polymer and FBR as the acceptor gave power conversion efficiencies (PCE) up to 4.1%. Transient and steady state optical spectroscopies indicated efficient, ultrafast charge generation and efficient photocurrent generation from both donor and acceptor. Ultrafast transient absorption spectroscopy was used to investigate polaron generation efficiency as well as recombination dynamics. It was determined that the P3HT:FBR blend is highly intermixed, leading to increased charge generation relative to comparative devices with P3HT:PC60BM, but also faster recombination due to a nonideal morphology in which, in contrast to P3HT:PC60BM devices, the acceptor does not aggregate enough to create appropriate percolation pathways that prevent fast nongeminate recombination. Despite this nonoptimal morphology the P3HT:FBR devices exhibit better performance than P3HT:PC60BM devices, used as control, demonstrating that this acceptor shows great promise for further optimization.
  • Journal article
    Shoaee S, Deledalle F, Tuladhar PS, Shivanna R, Rajaram S, Narayan KS, Durrant JRet al., 2015,

    A Comparison of Charge Separation Dynamics in Organic Blend Films Employing Fullerene and Perylene Diimide Electron Acceptors

    , JOURNAL OF PHYSICAL CHEMISTRY LETTERS, Vol: 6, Pages: 201-205, ISSN: 1948-7185
  • Journal article
    Wood S, Wade J, Shahid M, Collado-Fregoso E, Bradley DDC, Durrant JR, Heeney M, Kim J-Set 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
  • Journal article
    Shoaee S, Durrant JR, 2015,

    Oxygen diffusion dynamics in organic semiconductor films

    , JOURNAL OF MATERIALS CHEMISTRY C, Vol: 3, Pages: 10079-10084, ISSN: 2050-7526
  • Journal article
    Neri G, Walsh JJ, Wilson C, Reynal A, Lim JYC, Li X, White AJP, Long NJ, Durrant JR, Cowan AJet al., 2015,

    A functionalised nickel cyclam catalyst for CO2 reduction: electrocatalysis, semiconductor surface immobilisation and light-driven electron transfer

    , PHYSICAL CHEMISTRY CHEMICAL PHYSICS, Vol: 17, Pages: 1562-1566, ISSN: 1463-9076
  • Journal article
    Kim JS, Wood S, Shoaee S, Spencer SJ, Castro FA, Tsoi WC, Murphy CE, Sim M, Cho K, Durrant JR, Kim J-Set al., 2015,

    Morphology-performance relationships in polymer/fullerene blends probed by complementary characterisation techniques - effects of nanowire formation and subsequent thermal annealing

    , JOURNAL OF MATERIALS CHEMISTRY C, Vol: 3, Pages: 9224-9232, ISSN: 2050-7526
  • Journal article
    Shoaee S, Mehraeen S, Labram JG, Bredas J-L, Bradley DDC, Coropceanu V, Anthopoulos TD, Durrant JRet al., 2014,

    Correlating Non-Geminate Recombination with Film Structure: A Comparison of Polythiophene: Fullerene Bilayer and Blend Films

    , JOURNAL OF PHYSICAL CHEMISTRY LETTERS, Vol: 5, Pages: 3669-3676, ISSN: 1948-7185
  • Journal article
    Gevorgyan SA, Corazza M, Madsen MV, Bardizza G, Pozza A, Muellejans H, Blakesley JC, Dibb GFA, Castro FA, Trigo JF, Guillen CM, Herrero JR, Morvillo P, Maglione MG, Minarini C, Roca F, Cros S, Seraine C, Law CH, Tuladhar PS, Durrant JR, Krebs FCet al., 2014,

    Interlaboratory indoor ageing of roll-to-roll and spin coated organic photovoltaic devices: Testing the ISOS tests

    , POLYMER DEGRADATION AND STABILITY, Vol: 109, Pages: 162-170, ISSN: 0141-3910
  • Journal article
    Reynal A, Willkomm J, Muresan NM, Lakadamyali F, Planells M, Reisner E, Durrant Jet al., 2014,

    Distance dependent charge separation and recombination in semiconductor / molecular catalyst systems for water splitting

    , Chem. Commun., ISSN: 1359-7345
  • Journal article
    Credgington D, Liu S-W, Nelson J, Durrant JRet al., 2014,

    In Situ Measurement of Energy Level Shifts and Recombination Rates in Subphthalocyanine/C-60 Bilayer Solar Cells

    , JOURNAL OF PHYSICAL CHEMISTRY C, Vol: 118, Pages: 22858-22864, ISSN: 1932-7447
  • Journal article
    Foster S, Deledalle F, Mitani A, Kimura T, Kim K-B, Okachi T, Kirchartz T, Oguma J, Miyake K, Durrant JR, Doi S, Nelson Jet al., 2014,

    Electron Collection as a Limit to Polymer:PCBM Solar Cell Efficiency: Effect of Blend Microstructure on Carrier Mobility and Device Performance in PTB7:PCBM

    , ADVANCED ENERGY MATERIALS, Vol: 4, ISSN: 1614-6832
  • Journal article
    Schroeder BC, Li Z, Brady MA, Faria GC, Ashraf RS, Takacs CJ, Cowart JS, Duong DT, Chiu KH, Tan C-H, Cabral JT, Salleo A, Chabinyc ML, Durrant JR, McCulloch Iet al., 2014,

    Enhancing fullerene-based solar cell lifetimes by addition of a fullerene dumbbell

    , Angewandte Chemie-International Edition, Vol: 53, Pages: 12870-12875, ISSN: 1521-3773

    Cost-effective, solution-processable organic photovoltaics (OPV) present an interesting alternative to inorganic silicon-based solar cells. However, one of the major remaining challenges of OPV devices is their lack of long-term operational stability, especially at elevated temperatures. The synthesis of a fullerene dumbbell and its use as an additive in the active layer of a PCDTBT:PCBM-based OPV device is reported. The addition of only 20 % of this novel fullerene not only leads to improved device efficiencies, but more importantly also to a dramatic increase in morphological stability under simulated operating conditions. Dynamic secondary ion mass spectrometry (DSIMS) and TEM are used, amongst other techniques, to elucidate the origins of the improved morphological stability.
  • Journal article
    Law C, Miseikis L, Dimitrov S, Shakya-Tuladhar P, Li X, Barnes PRF, Durrant J, O'Regan BCet al., 2014,

    Performance and Stability of Lead Perovskite/TiO2, Polymer/PCBM, and Dye Sensitized Solar Cells at Light Intensities up to 70 Suns

    , ADVANCED MATERIALS, Vol: 26, Pages: 6268-6273, ISSN: 0935-9648
  • Journal article
    Pendlebury SR, Wang X, Le Formal F, Cornuz M, Kafizas A, Tilley SD, Graetzel M, Durrant JRet al., 2014,

    Ultrafast charge carrier recombination and trapping in hematite photoanodes under applied bias

    , Journal of the American Chemical Society, Vol: 136, Pages: 9854-9857, ISSN: 0002-7863

    Transient absorption spectroscopy on subpicosecond to second time scales is used to investigate photogenerated charge carrier recombination in Si-doped nanostructured hematite (α-Fe2O3) photoanodes as a function of applied bias. For unbiased hematite, this recombination exhibits a 50% decay time of ∼6 ps, ∼103 times faster than that of TiO2 under comparable conditions. Anodic bias significantly retards hematite recombination dynamics, and causes the appearance of electron trapping on ps−μs time scales. These ultrafast recombination dynamics, their retardation by applied bias, and the associated electron trapping are discussed in terms of their implications for efficient water oxidation.
  • Journal article
    Deledalle F, Shakya Tuladhar P, Nelson J, Durrant JR, Kirchartz Tet al., 2014,

    Understanding the Apparent Charge Density Dependence of Mobility and Lifetime in Organic Bulk Heterojunction Solar Cells

    , The Journal of Physical Chemistry C, Vol: 118, Pages: 8837-8842, ISSN: 1932-7447
  • Journal article
    Dimitrov SD, Huang Z, Deledalle F, Nielsen CB, Schroeder BC, Ashraf RS, Shoaee S, McCulloch I, Durrant JRet al., 2014,

    Towards optimisation of photocurrent from fullerene excitons in organic solar cells

    , ENERGY & ENVIRONMENTAL SCIENCE, Vol: 7, Pages: 1037-1043, ISSN: 1754-5692
  • Journal article
    Gevorgyan SA, Zubillaga O, Maria Vega de Seoane J, Machado M, Parlak EA, Tore N, Voroshazi E, Aernouts T, Muellejans H, Bardizza G, Taylor N, Verhees W, Kroon JM, Morvillo P, Minarini C, Roca F, Castro FA, Cros S, Lechene B, Trigo JF, Guillen C, Herrero J, Zimmermann B, Sapkota SB, Veit C, Wuerfel U, Tuladhar PS, Durrant JR, Winter S, Rousu S, Valimaki M, Hinrichs V, Cowan SR, Olson DC, Sommer-Larsen P, Krebs FCet al., 2014,

    Round robin performance testing of organic photovoltaic devices

    , RENEWABLE ENERGY, Vol: 63, Pages: 376-387, ISSN: 0960-1481
  • Journal article
    Soon YW, Shoaee S, Ashraf RS, Bronstein H, Schroeder BC, Zhang W, Fei Z, Heeney M, McCulloch I, Durrant JRet al., 2014,

    Material Crystallinity as a Determinant of Triplet Dynamics and Oxygen Quenching in Donor Polymers for Organic Photovoltaic Devices

    , ADVANCED FUNCTIONAL MATERIALS, Vol: 24, Pages: 1474-1482, ISSN: 1616-301X
  • Journal article
    Buchaca-Domingo E, Ferguson AJ, Jamieson FC, McCarthy-Ward T, Shoaee S, Tumbleston JR, Reid OG, Yu L, Madec M-B, Pfannmoeller M, Hermerschmidt F, Schroeder RR, Watkins SE, Kopidakis N, Portale G, Amassian A, Heeney M, Ade H, Rumbles G, Durrant JR, Stingelin Net al., 2014,

    Additive-assisted supramolecular manipulation of polymer:fullerene blend phase morphologies and its influence on photophysical processes

    , MATERIALS HORIZONS, Vol: 1, Pages: 270-279, ISSN: 2051-6347
  • Journal article
    Le Formal F, Pendlebury SR, Cornuz M, Tilley SD, Graetzel M, Durrant JRet al., 2014,

    Back electron-hole recombination in hematite photoanodes for water splitting

    , Journal of the American Chemical Society, Vol: 136, Pages: 2564-2574, ISSN: 0002-7863

    The kinetic competition between electron–hole recombination and water oxidation is a key consideration for the development of efficient photoanodes for solar driven water splitting. In this study, we employed three complementary techniques, transient absorption spectroscopy (TAS), transient photocurrent spectroscopy (TPC), and electrochemical impedance spectroscopy (EIS), to address this issue for one of the most widely studied photoanode systems: nanostructured hematite thin films. For the first time, we show a quantitative agreement between all three techniques. In particular, all three methods show the presence of a recombination process on the 10 ms to 1 s time scale, with the time scale and yield of this loss process being dependent upon applied bias. From comparison of data between these techniques, we are able to assign this recombination phase to recombination of bulk hematite electrons with long-lived holes accumulated at the semiconductor/electrolyte interface. The data from all three techniques are shown to be consistent with a simple kinetic model based on competition between this, bias dependent, recombination pathway and water oxidation by these long-lived holes. Contrary to most existing models, this simple model does not require the consideration of surface states located energetically inside the band gap. These data suggest two distinct roles for the space charge layer developed at the semiconductor/electrolyte interface under anodic bias. Under modest anodic bias (just anodic of flatband), this space charge layer enables the spatial separation of initially generated electrons and holes following photon absorption, generating relatively long-lived holes (milliseconds) at the semiconductor surface. However, under such modest bias conditions, the energetic barrier generated by the space charge layer field is insufficient to prevent the subsequent recombination of these holes with electrons in the semiconductor bulk on a time scale faster than wa

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