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  • Journal article
    Tuladhar SM, Azzouzi M, Delval F, Yao J, Guilbert AAY, Kirchartz T, Montcada NF, Dominguez R, Langa F, Palomares E, Nelson Jet al., 2016,

    Low Open-Circuit Voltage Loss in Solution Processed Small Molecule Organic Solar Cells

    , ACS Energy Letters, Vol: 1, Pages: 302-308, ISSN: 2380-8195
  • Journal article
    Gambhir A, Sandwell P, Nelson J, 2016,

    The future costs of OPV - A bottom-up model of material and manufacturing costs with uncertainty analysis

    , Solar Energy Materials and Solar Cells, Vol: 156, Pages: 49-58, ISSN: 0927-0248

    Organic photovoltaic (OPV) technology has the potential to provide cheap solar electricity, given advances in low-cost production and module efficiency and lifetime. However, several uncertainties remain in terms of the future costs of OPV modules, which depend on future material and manufacturing costs, as well as key performance characteristics. This assessment takes an engineering-based approach to assessing the potential future cost of each component of OPV modules, as well as the future scale of OPV production plants and associated scale economies, using stochastic analysis to account for uncertainty. The analysis suggests that OPV module costs could fall within a (interquartile) range of US$0.23–0.34/Wp, with a median cost estimate of US$0.28/Wp in the near-term, with future costs most sensitive to manufacturing scale, cell efficiency and module fill factor. This compares to a projected range of module costs for more established PV technologies (crystalline silicon, cadmium telluride and copper indium gallium selenide) of US$0.35–0.6/Wp by 2020. In levelised cost of electricity terms, OPV could compete with the established technologies in both roof- and ground-mounted systems if it can achieve a 10-year lifetime.

  • Journal article
    Guilbert AA, Zbiri M, Jenart MV, Nielsen CB, Nelson Jet al., 2016,

    New insights into the molecular dynamics of P3HT:PCBM bulk heterojunction: a time-of-flight quasi-elastic neutron scattering study

    , Journal of Physical Chemistry Letters, Vol: 7, Pages: 2252-2257, ISSN: 1948-7185

    The molecular dynamics of organic semiconductor blend layers are likely to affect the optoelectronic properties and the performance of devices such as solar cells. We study the dynamics (5-50 ps) of the poly(3-hexylthiophene) (P3HT): phenyl-C61-butyric acid methyl ester (PCBM) blend by time-of-flight quasi-elastic neutron scattering, at temperatures in the range 250-360 K, thus spanning the glass transition temperature region of the polymer and the operation temperature of an OPV device. The behavior of the QENS signal provides evidence for the vitrification of P3HT upon blending, especially above the glass transition temperature, and the plasticization of PCBM by P3HT, both dynamics occurring on the picosecond time scale.

  • Journal article
    Vezie M, Few S, Meager I, Pieridou G, Dörling B, Ashraf RA, Goñi AR, Bronstein H, McCulloch I, Hayes SC, Campoy-Quiles M, Nelson Jet al., 2016,

    Exploring the origin of high optical absorption in conjugated polymers

    , Nature Materials, Vol: 15, Pages: 746-753, ISSN: 1476-4660

    The specific optical absorption of an organic semiconductor is critical to the performance of organic optoelectronic devices. For example, higher light-harvesting efficiency can lead to higher photocurrent in solar cells that are limited by sub-optimal electrical transport. Here, we compare over 40 conjugated polymers, and find that many different chemical structures share an apparent maximum in their extinction coefficients. However, a diketopyrrolopyrrole-thienothiophene copolymer shows remarkably high optical absorption at relatively low photon energies. By investigating its backbone structure and conformation with measurements and quantum chemical calculations, we find that the high optical absorption can be explained by the high persistence length of the polymer. Accordingly, we demonstrate high absorption in other polymers with high theoretical persistence length. Visible light harvesting may be enhanced in other conjugated polymers through judicious design of the structure.

  • Journal article
    Sandwell P, Chan NLA, Foster S, Nagpal D, Emmott CJM, Candelise C, Buckle SJ, Ekins-Daukes N, Gambhir A, Nelson Jet al., 2016,

    Off-grid solar photovoltaic systems for rural electrification and emissions mitigation in India

    , Solar Energy Materials and Solar Cells, Vol: 156, Pages: 147-156, ISSN: 0927-0248

    Over one billion people lack access to electricity and many of them in rural areas far from existing infrastructure. Off-grid systems can provide an alternative to extending the grid network and using renewable energy, for example solar photovoltaics (PV) and battery storage, can mitigate greenhouse gas emissions from electricity that would otherwise come from fossil fuel sources. This paper presents a model capable of comparing several mature and emerging PV technologies for rural electrification with diesel generation and grid extension for locations in India in terms of both the levelised cost and lifecycle emissions intensity of electricity. The levelised cost of used electricity, ranging from $0.46–1.20/kWh, and greenhouse gas emissions are highly dependent on the PV technology chosen, with battery storage contributing significantly to both metrics. The conditions under which PV and storage becomes more favourable than grid extension are calculated and hybrid systems of PV, storage and diesel generation are evaluated. Analysis of expected price evolutions suggest that the most cost-effective hybrid systems will be dominated by PV generation around 2018.

  • Journal article
    Kirchartz T, Nelson J, Rau U, 2016,

    Reciprocity between Charge Injection and Extraction and Its Influence on the Interpretation of Electroluminescence Spectra in Organic Solar Cells

    , PHYSICAL REVIEW APPLIED, Vol: 5, ISSN: 2331-7019
  • Journal article
    Emmott CJM, Moia D, Sandwell P, Ekins-Daukes N, Hosel M, Lukoschek L, Amarasinghe C, Krebs FC, Nelson Jet al., 2016,

    In-situ, long-term operational stability of organic photovoltaics for off-grid applications in Africa

    , Solar Energy Materials and Solar Cells, Vol: 149, Pages: 284-293, ISSN: 0927-0248
  • Journal article
    Ben Dkhil S, Gaceur M, Dachraoui W, Hannani D, Fall S, Brunel F, Wang M, Poize G, Mawyin J, Shupyk I, Martini C, Shilova E, Fages F, Ishwara T, Nelson J, Watanabe T, Yoshimoto N, Margeat O, Videlot-Ackermann C, Ackermann Jet al., 2016,

    P-type semiconductor surfactant modified zinc oxide nanorods for hybrid bulk heterojunction solar cells

    , Solar Energy Materials and Solar Cells, Vol: 159, Pages: 608-616, ISSN: 0927-0248

    In this work, hybrid bulk heterojunction solar cells based on surfactant-modified zinc oxide nanorods (ZnO NRs) blended with poly-(3-hexylthiophene) (P3HT) are presented. (E)-2-cyano-3-(5′-(4-(dibutylamino)styryl)-2,2′-bithiophen-5-yl)acrylic acid (1), a p-type semiconductor, is used as grafted interfacial surfactant on ZnO NRs, named 1-ZnO NRs, in order to improve simultaneously the nanoscale morphology of the hybrid polymer blend as well as the electronic properties of the heterojunction interface. Our studies reveal that the ligand modification of ZnO NRs leads to strongly improved aggregate free P3HT/ZnO blends that show five time increased power conversion efficiency and corresponding photo-generated charge carrier transport compared to untreated ZnO NRs. From transient absorption spectroscopy, it was found that recombination kinetics were similar in the device using untreated ZnO and modified 1-ZnO NRs, respectively, pointing to a major impact of the ligand in the improvement of the blend morphology. Corresponding device optimization led to improvements of FF and Voc to values comparable to P3HT blends using fullerene acceptors, but photocurrent density of the P3HT/1-ZnO solar cells was found low even after optimization. The latter could be addressed to destruction of long range organization of P3HT induced by the presence of the ZnO NRs as well as low electron transport inside the blend.

  • Conference paper
    Hayes SC, Pieridou G, Vezie M, Few S, Bronstein H, Meager I, McCulloch I, Nelson Jet al., 2016,

    Effect of molecular weight on the vibronic structure of a diketopyrrolopyrrole polymer

    , Conference on Physical Chemistry of Interfaces and Nanomaterials XV, Publisher: SPIE-INT SOC OPTICAL ENGINEERING, ISSN: 0277-786X
  • Journal article
    Vaissier V, Frost JM, Barnes PRF, Nelson Jet al., 2015,

    Influence of Intermolecular Interactions on the Reorganization Energy of Charge Transfer between Surface-Attached Dye Molecules

    , JOURNAL OF PHYSICAL CHEMISTRY C, Vol: 119, Pages: 24337-24341, ISSN: 1932-7447

    The parameters controlling the kinetics ofintermolecular charge transfer are traditionally estimatedfrom electronic structure calculations on the charge donorand charge acceptor in isolation. Here, we show that thisprocedure results in inaccuracies for hole transfer between apair of organic dye molecules by comparing charge-constraineddensity functional theory (DFT) calculations on a dyecation/neutral dye pair to the conventional DFT calculationson the isolated molecules. We quantify the error made in thereorganization energy of hole exchange between dye molecules(λi). We choose three indolene-based organic dyes with application to dye-sensitized solar cells, namely, D149, D102, and D131,for which experimental values of λ are available. We find that, although highly system dependent, the intermolecular interactionbetween the charge donor and acceptor can lead to a 0.25 eV change in λi, illustrating the limitations of the widely used originalmethod in predicting the rate of charge transfer.

  • Journal article
    Guilbert AAY, Urbina A, Abad J, Diaz-Paniagua C, Batallan F, Seydel T, Zbiri M, Garcia-Sakai V, Nelson Jet al., 2015,

    Temperature-dependent dynamics of polyalkylthiophene conjugated polymers: a combined neutron scattering and simulation study

    , Chemistry of Materials, Vol: 27, Pages: 7652-7661, ISSN: 1520-5002

    The dynamics of conjugated polymers are known to influence the performance of optoelectronic devices. Polyalkylthiophenes are a widely studied class of conjugated polymers, which exhibit a glass transition around room temperature and consequently are sensitive to temperature variations. We studied the dynamics of two polyalkylthiophenes of different side chain lengths (hexyl and octyl) as a function of temperature, by comparing their quasi-elastic neutron scattering (QENS) with molecular dynamics simulations (MD). We found a good agreement between the simulated and experimental data within the explored time window (of ∼4 ns), demonstrating that the force fields used in MD simulations are appropriate and that the QENS technique can be used as a validation of such force fields. Using MD allows us to identify and to assign contributions to the QENS signal from different parts of the polymers and to determine the activation energies of the different motions.

  • Journal article
    Moia D, Leijtens T, Noel N, Snaith HJ, Nelson J, Barnes PRFet al., 2015,

    Dye Monolayers Used as the Hole Transporting Medium in Dye-Sensitized Solar Cells

    , ADVANCED MATERIALS, Vol: 27, Pages: 5889-5894, ISSN: 0935-9648
  • Journal article
    Leguy AMA, Azarhoosh P, Alonso MI, Campoy-Quiles M, Weber OJ, Yao J, Bryant D, Weller MT, Nelson J, Walsh A, van Schilfgaarde M, Barnes PRFet al., 2015,

    Experimental and theoretical optical properties of methylammonium lead halide perovskites

    , Nanoscale, Vol: 8, Pages: 6317-6327, ISSN: 2040-3372
  • Journal article
    Wheeler, Deledalle F, Tokmoldin N, Kirchartz T, Nelson J, Durrant Jet al., 2015,

    Influence of Surface Recombination on Charge-Carrier Kinetics in Organic Bulk Heterojunction Solar Cells with Nickel Oxide Interlayers

    , Physical review applied, Vol: 4, ISSN: 2331-7019

    The choice of electrode for organic photovoltaics is known to be of importance to both device stability and performance, especially regarding the open-circuit voltage (VOC). Here we show that the work function of a nickel oxide anode, varied using an O2 plasma treatment, has a considerable influence on the open-circuit voltage VOC of an organic solar cell. We probe recombination in the devices using transient photovoltage and charge extraction to determine the lifetime as a function of charge-carrier concentration and compare the experimental results with numerical drift-diffusion simulations. This combination of experiment and simulations allows us to conclude that the variations in VOC are due to a change in surface recombination, localized at the NiO anode, although only a small change in carrier lifetime is observed.

  • Journal article
    Baran D, Vezie MS, Gasparini N, Deledalle F, Yao J, Schroeder BC, Bronstein H, Ameri T, Kirchartz T, McCulloch I, Nelson J, Brabec CJet al., 2015,

    Role of Polymer Fractionation in Energetic Losses and Charge Carrier Lifetimes of Polymer: Fullerene Solar Cells

    , JOURNAL OF PHYSICAL CHEMISTRY C, Vol: 119, Pages: 19668-19673, ISSN: 1932-7447
  • Journal article
    Moia D, Cappel UB, Leijtens T, Li X, Telford AM, Snaith HJ, O'Regan BC, Nelson J, Barnes PRFet al., 2015,

    The Role of Hole Transport between Dyes in Solid-State Dye-Sensitized Solar Cells

    , Journal of Physical Chemistry C, Vol: 119, Pages: 18975-18985, ISSN: 1932-7447
  • Journal article
    Yao J, Kirchartz T, Vezie MS, Faist MA, Gong W, He Z, Wu H, Troughton J, Watson T, Bryant D, Nelson Jet al., 2015,

    Quantifying Losses in Open-Circuit Voltage in Solution-Processable Solar Cells

    , PHYSICAL REVIEW APPLIED, Vol: 4, ISSN: 2331-7019
  • Journal article
    Leguy AMA, Frost JM, McMahon AP, Sakai VG, Kockelmann W, Law C, Li X, Foglia F, Walsh A, O'Regan BC, Nelson J, Cabral JT, Barnes PRFet al., 2015,

    Corrigendum: The dynamics of methylammonium ions in hybrid organic–inorganic perovskite solar cells

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

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