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  • Journal article
    Leguy AMA, Frost JM, McMahon AP, Sakai VG, Kochelmann W, Law C, Li X, Foglia F, Walsh A, O'Regan BC, Nelson J, Cabral JT, Barnes PRFet al., 2015,

    The dynamics of methylammonium ions in hybrid organic-inorganic perovskite solar cells

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

    Methylammonium lead iodide perovskite can make high-efficiency solar cells, which also show an unexplained photocurrent hysteresis dependent on the device-poling history. Here we report quasielastic neutron scattering measurements showing that dipolar CH3NH3+ ions reorientate between the faces, corners or edges of the pseudo-cubic lattice cages in CH3NH3PbI3 crystals with a room temperature residence time of ~14 ps. Free rotation, π-flips and ionic diffusion are ruled out within a 1–200-ps time window. Monte Carlo simulations of interacting CH3NH3+ dipoles realigning within a 3D lattice suggest that the scattering measurements may be explained by the stabilization of CH3NH3+ in either antiferroelectric or ferroelectric domains. Collective realignment of CH3NH3+ to screen a device’s built-in potential could reduce photovoltaic performance. However, we estimate the timescale for a domain wall to traverse a typical device to be ~0.1–1 ms, faster than most observed hysteresis.

  • Journal article
    Leguy AMA, Hu Y, Campoy-Quiles M, Isabel Alonso M, Weber OJ, Azarhoosh P, van Schilfgaarde M, Weller MT, Bein T, Nelson J, Docampo P, Barnes PRFet al., 2015,

    Reversible hydration of CH(3)NH(3)Pbl(3) in films, single crystals, and solar cells

    , Chemistry of Materials, Vol: 27, Pages: 3397-3407, ISSN: 0897-4756

    Solar cells composed of methylammonium lead iodide perovskite (MAPI) are notorious for their sensitivity to moisture. We show that (i) hydrated crystal phases are formed when MAPI is exposed to water vapor at room temperature and (ii) these phase changes are fully reversed when the material is subsequently dried. The reversible formation of CH3NH3PbI3·H2O followed by (CH3NH3)4PbI6·2H2O (upon long exposure times) was observed using time-resolved XRD and ellipsometry of thin films prepared using “solvent engineering”, single crystals, and state-of-the-art solar cells. In contrast to water vapor, the presence of liquid water results in the irreversible decomposition of MAPI to form PbI2. MAPI changes from dark brown to transparent on hydration; the precise optical constants of CH3NH3PbI3·H2O formed on single crystals were determined, with a bandgap at 3.1 eV. Using the single-crystal optical constants and thin-film ellipsometry measurements, the time-dependent changes to MAPI films exposed to moisture were modeled. The results suggest that the monohydrate phase forms independent of the depth in the film, suggesting rapid transport of water molecules along grain boundaries. Vapor-phase hydration of an unencapsulated solar cell (initially Jsc ≈ 19 mA cm–2 and Voc ≈ 1.05 V at 1 sun) resulted in more than a 90% drop in short-circuit photocurrent and ∼200 mV loss in open-circuit potential; however, these losses were fully reversed after the device was exposed to dry nitrogen for 6 h. Hysteresis in the current–voltage characteristics was significantly increased after this dehydration, which may be related to changes in the defect density and morphology of MAPI following recrystallization from the hydrate. Based on our observations, we suggest that irreversible decomposition of MAPI in the presence of water vapor only occurs significantly once a grain has been fully converted to the monohydrate phase.

  • 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
    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
    Emmott CJM, Roehr JA, Campoy-Quiles M, Kirchartz T, Urbina A, Ekins-Daukes NJ, Nelson Jet al., 2015,

    Organic photovoltaic greenhouses: a unique application for semi-transparent PV?

    , Energy & Environmental Science, Vol: 8, Pages: 1317-1328, ISSN: 1754-5706

    Organic photovoltaics are an emerging solar power technology which embody properties such astransparency, flexibility, and rapid, roll to roll manufacture, opening the potential for unique nicheapplications. We report a detailed techno-economic analysis of one such application, namely thephotovoltaic greenhouse, and discuss whether the unique properties of the technology can provideadvantages over conventional photovoltaics. The potential for spectral selectivity through the choice ofOPV materials is evaluated for the case of a photovoltaic greenhouse. The action spectrum of typicalgreenhouse crops is used to determine the impact on crop growth of blocking different spectral rangesfrom the crops. Transfer matrix optical modelling is used to assess the efficiency and spectrally resolvedtransparency of a variety of commercially available semi-conducting polymer materials, in addition to anon-commercial low-band-gap material with absorption outside that required for crop growth. Economicanalysis suggests there could be a huge potential for OPV greenhouses if aggressive cost targets can bemet. Technical analysis shows that semi-transparent OPV devices may struggle to perform better thanopaque crystalline silicon with partial coverage, however, OPV devices using the low-band-gap materialPMDPP3T, as well as a high efficiency mid-band-gap polymer PCDTBT, can demonstrate improvedperformance in comparison to opaque, flexible thin-film modules such as CIGS. These results stress theimportance of developing new, highly transparent electrode and interlayer materials, along with highefficiency active layers, if the full potential of this application is going to be realised.

  • Journal article
    Few S, Frost JM, Nelson J, 2015,

    Models of charge pair generation in organic solar cells

    , PHYSICAL CHEMISTRY CHEMICAL PHYSICS, Vol: 17, Pages: 2311-2325, ISSN: 1463-9076
  • Journal article
    Dattani R, Gibson KF, Few S, Borg AJ, DiMaggio PA, Nelson J, Kazarian SG, Cabral JTet al., 2015,

    Fullerene oxidation and clustering in solution induced by light

    , Journal of Colloid and Interface Science, Vol: 446, Pages: 24-30, ISSN: 1095-7103

    We investigate the environmental stability of fullerene solutions by static and dynamic light scattering, FTIR, NMR and mass spectroscopies, and quantum chemical calculations. We find that visible light exposure of fullerene solutions in toluene, a good solvent, under ambient laboratory conditions results in C60 oxidation to form fullerene epoxides, and subsequently causes fullerene clustering in solution. The clusters grow with time, even in absence of further illumination, and can reach dimensions from ≈100 nm to the μm scale over ≈1 day. Static light scattering suggests that resulting aggregates are fractal, with a characteristic power law (df) that increases from approximately 1.3 to 2.0 during light exposure. The clusters are bound by weak Coulombic interactions and are found to be reversible, disintegrating by mechanical agitation and thermal stress, and reforming over time. Our findings are relevant to the solution processing of composites and organic photovoltaics, whose reproducibility and performance requires control of fullerene solution stability under storage conditions.

  • Journal article
    MacLachlan AJ, Rath T, Cappel UB, Dowland SA, Amenitsch H, Knall A-C, Buchmaier C, Trimmel G, Nelson J, Haque SAet al., 2015,

    Polymer/Nanocrystal Hybrid Solar Cells: Influence of Molecular Precursor Design on Film Nanomorphology, Charge Generation and Device Performance

    , ADVANCED FUNCTIONAL MATERIALS, Vol: 25, Pages: 409-420, ISSN: 1616-301X
  • 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
    Manke F, Frost JM, Vaissier V, Nelson J, Barnes PRFet al., 2015,

    Influence of a nearby substrate on the reorganization energy of hole exchange between dye molecules

    , PHYSICAL CHEMISTRY CHEMICAL PHYSICS, Vol: 17, Pages: 7345-7354, ISSN: 1463-9076
  • Journal article
    Steiner F, Foster S, Losquin A, Labram J, Anthopoulos TD, Frost JM, Nelson Jet al., 2015,

    Distinguishing the influence of structural and energetic disorder on electron transport in fullerene multi-adducts

    , MATERIALS HORIZONS, Vol: 2, Pages: 113-119, ISSN: 2051-6347
  • Journal article
    Hermerschmidt F, Kalogirou AS, Min J, Zissimou GA, Tuladhar SM, Ameri T, Faber H, Itskos G, Choulis SA, Anthopoulos TD, Bradley DDC, Nelson J, Brabec CJ, Koutentis PAet al., 2015,

    4H-1,2,6-Thiadiazin-4-one-containing small molecule donors and additive effects on their performance in solution-processed organic solar cells

    , JOURNAL OF MATERIALS CHEMISTRY C, Vol: 3, Pages: 2358-2365, ISSN: 2050-7526
  • Journal article
    Wade J, Steiner F, Niedzialek D, James DT, Jung Y, Yun D-J, Bradley DDC, Nelson J, Kim J-Set 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
  • Journal article
    Guilbert AAY, Schmidt M, Bruno A, Yao J, King S, Tuladhar SM, Kirchartz T, Alonso MI, Goni AR, Stingelin N, Haque SA, Campoy-Quiles M, Nelson Jet al., 2014,

    Spectroscopic Evaluation of Mixing and Crystallinity of Fullerenes in Bulk Heterojunctions

    , ADVANCED FUNCTIONAL MATERIALS, Vol: 24, Pages: 6972-6980, ISSN: 1616-301X
  • Journal article
    Madsen MV, Gevorgyan SA, Pacios R, Ajuria J, Etxebarria I, Kettle J, Bristow ND, Neophytou M, Choulis SA, Roman LS, Yohannes T, Cester A, Cheng P, Zhan X, Wu J, Xie Z, Tu W-C, He J-H, Fell CJ, Anderson K, Hermenau M, Bartesaghi D, Koster LJA, Machui F, Gonzalez-Valls I, Lira-Cantu M, Khlyabich PP, Thompson BC, Gupta R, Shanmugam K, Kulkarni GU, Galagan Y, Urbina A, Abad J, Roesch R, Hoppe H, Morvillo P, Bobeico E, Panaitescu E, Menon L, Luo Q, Wu Z, Ma C, Hambarian A, Melikyan V, Hambsch M, Burn PL, Meredith P, Rath T, Dunst S, Trimmel G, Bardizza G, Muellejans H, Goryachev AE, Misra RK, Katz EA, Takagi K, Magaino S, Saito H, Aoki D, Sommeling PM, Kroon JM, Vangerven T, Manca J, Kesters J, Maes W, Bobkova OD, Trukhanov VA, Paraschuk DY, Castro FA, Blakesley J, Tuladhar SM, Roehr JA, Nelson J, Xia J, Parlak EA, Tumay TA, Egelhaaf H-J, Tanenbaum DM, Ferguson GM, Carpenter R, Chen H, Zimmermann B, Hirsch L, Wantz G, Sun Z, Singh P, Bapat C, Offermans T, Krebs FCet al., 2014,

    Worldwide outdoor round robin study of organic photovoltaic devices and modules

    , SOLAR ENERGY MATERIALS AND SOLAR CELLS, Vol: 130, Pages: 281-290, ISSN: 0927-0248
  • 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
    Kirchartz T, Nelson J, 2014,

    Device Modelling of Organic Bulk Heterojunction Solar Cells

    , MULTISCALE MODELLING OF ORGANIC AND HYBRID PHOTOVOLTAICS, Vol: 352, Pages: 279-324, ISSN: 0340-1022
  • Journal article
    Vaissier V, Mosconi E, Moia D, Pastore M, Frost JM, De Angelis F, Barnes PRF, Nelson Jet al., 2014,

    Effect of Molecular Fluctuations on Hole Diffusion within Dye Monolayers

    , CHEMISTRY OF MATERIALS, Vol: 26, Pages: 4731-4740, ISSN: 0897-4756
  • Book chapter
    Ekins-Daukes NJ, Nelson J, 2014,

    Quantum Well Solar Cells

    , Clean Electricity from Photovoltaics, Editors: Green, Archer, Publisher: Imperial College Press, ISBN: 9781848167674

    The second edition of Clean Electricity from Photovoltaics, first published in 2001, provides an updated account of the underlying science, technology and market prospects for photovoltaics.

  • Journal article
    Dattani R, Bannock JH, Fei Z, MacKenzie RCI, Guilbert AAY, Vezie MS, Nelson J, de Mello JC, Heeney M, Cabral JT, Nedoma AJet 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
  • Journal article
    Martinez L, Higuchi S, MacLachlan AJ, Stavrinadis A, Miller NC, Diedenhofen SL, Bernechea M, Sweetnam S, Nelson J, Haque SA, Tajima K, Konstantatos Get al., 2014,

    Improved electronic coupling in hybrid organic-inorganic nanocomposites employing thiol-functionalized P3HT and bismuth sulfide nanocrystals

    , Nanoscale, Vol: 6, Pages: 10018-10026, ISSN: 2040-3372

    In this study, we employ a thiol-functionalized polymer (P3HT-SH) as a leverage to tailor the nanomorphology and electronic coupling in polymer–nanocrystal composites for hybrid solar cells. The presence of the thiol functional group allows for a highly crystalline semiconducting polymer film at low thiol content and allows for improved nanomorphologies in hybrid organic–inorganic systems when employing non-toxic bismuth sulfide nanocrystals. The exciton dissociation efficiency and carrier dynamics at this hybrid heterojunction are investigated through photoluminescence quenching and transient absorption spectroscopy measurements, revealing a larger degree of polaron formation when P3HT-SH is employed, suggesting an increased electronic interaction between the metal chalcogenide nanocrystals and the thiol-functionalized P3HT. The fabricated photovoltaic devices show 15% higher power conversion efficiencies as a result of the improved nanomorphology and better charge transfer mechanism together with the higher open circuit voltages arising from the deeper energy levels of P3HT-SH.

  • Journal article
    Xu W, Zhang X, Hu Q, Zhao L, Teng X, Lai W-Y, Xia R, Nelson J, Huang W, Bradley DDCet al., 2014,

    Fluorene-based cathode interlayer polymers for high performance solution processed organic optoelectronic devices

    , ORGANIC ELECTRONICS, Vol: 15, Pages: 1244-1253, ISSN: 1566-1199
  • Journal article
    Emmott CJM, Ekins-Daukes NJ, Nelson J, 2014,

    Dynamic carbon mitigation analysis: the role of thin-film photovoltaics

    , ENERGY & ENVIRONMENTAL SCIENCE, Vol: 7, Pages: 1810-1818, ISSN: 1754-5692
  • Journal article
    MacKenzie RCI, Goeritz A, Greedy S, von Hauff E, Nelson Jet al., 2014,

    Theory of Stark spectroscopy transients from thin film organic semiconducting devices

    , PHYSICAL REVIEW B, Vol: 89, ISSN: 2469-9950
  • Journal article
    Few S, Frost JM, Kirkpatrick J, Nelson Jet al., 2014,

    Influence of Chemical Structure on the Charge Transfer State Spectrum of a Polymer:Fullerene Complex

    , JOURNAL OF PHYSICAL CHEMISTRY C, Vol: 118, Pages: 8253-8261, ISSN: 1932-7447
  • Journal article
    MacLachlan AJ, O'Mahony FTF, Sudlow AL, Hill MS, Molloy KC, Nelson J, Haque SAet al., 2014,

    Solution- Processed Mesoscopic Bi2S3: Polymer Photoactive Layers

    , CHEMPHYSCHEM, Vol: 15, Pages: 1019-1023, ISSN: 1439-4235
  • 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
    Abramavicius V, Vithanage DA, Devizis A, Infahsaeng Y, Bruno A, Foster S, Keivanidis PE, Abramavicius D, Nelson J, Yartsev A, Sundstroem V, Gulbinas Vet al., 2014,

    Carrier motion in as-spun and annealed P3HT:PCBM blends revealed by ultrafast optical electric field probing and Monte Carlo simulations

    , PHYSICAL CHEMISTRY CHEMICAL PHYSICS, Vol: 16, Pages: 2686-2692, ISSN: 1463-9076
  • Journal article
    Guilbert AAY, Frost JM, Agostinelli T, Pires E, Lilliu S, Macdonald JE, Nelson Jet al., 2014,

    Influence of Bridging Atom and Side Chains on the Structure and Crystallinity of Cyclopentadithiophene-Benzothiadiazole Polymers

    , CHEMISTRY OF MATERIALS, Vol: 26, Pages: 1226-1233, ISSN: 0897-4756

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