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Journal articleYang H, Tam B, Colovic M, et al., 2017,
Addressing Chirality in the Structure and Synthesis of [<SUP>18</SUP>F]5-Fluoroaminosuberic Acid ([<SUP>18</SUP>F]FASu)
, CHEMISTRY-A EUROPEAN JOURNAL, Vol: 23, Pages: 11100-11107, ISSN: 0947-6539- Author Web Link
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- Citations: 6
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Journal articleRodriguez-Martinez X, Vezie MS, Shi X, et al., 2017,
Quantifying local thickness and composition in thin films of organic photovoltaic blends by Raman scattering
, Journal of Materials Chemistry C, Vol: 5, Pages: 7270-7282, ISSN: 2050-7526We report a methodology based on Raman spectroscopy that enables the non-invasive and fast quantitative determination of local thickness and composition in thin films (from a few monolayers to hundreds of nm) of one or more components. We apply our methodology to blends of organic conjugated materials relevant in the field of organic photovoltaics. As a first step, we exploit the transfer-matrix formalism to describe the Raman process in thin films including reabsorption and interference effects of the incoming and scattered electric fields. This allows determining the effective solid-state Raman cross-section of each material by studying the dependence of the Raman intensity on film thickness. These effective cross sections are then used to estimate the local thickness and composition in a series of polymer:fullerene blends. We find that the model is accurate within ±10 nm in thickness and ±5 vol% in composition provided that (i) the film thickness is kept below the thickness corresponding to the first maximum of the calculated Raman intensity oscillation; (ii) the materials making up the blend show close enough effective Raman cross-sections; and (iii) the degree of order attained by the conjugated polymer in the blend is similar to that achieved when cast alone. Our methodology opens the possibility of making quantitative maps of composition and thickness over large areas (from microns to centimetres squared) with diffraction-limited resolution and in any multi-component system based thin film technology.
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Journal articleSpeller EM, McGettrick JD, Rice B, et al., 2017,
Impact of Aggregation on the Photochemistry of Fullerene Films: Correlating Stability to Triplet Exciton Kinetics
, ACS APPLIED MATERIALS & INTERFACES, Vol: 9, Pages: 22739-22747, ISSN: 1944-8244 -
Journal articleFew SPM, Chia C, Teo D, et al., 2017,
The impact of chemical structure and molecular packing on the electronic polarisation of fullerene arrays
, Physical Chemistry Chemical Physics, Vol: 19, Pages: 18709-18720, ISSN: 1463-9084Electronic polarisation contributes to the electronic landscape as seen by separating charges in organic materials. The nature of electronic polarisation depends on the polarisability, density, and arrangement of polarisable molecules. In this paper, we introduce a microscopic, coarse-grained model in which we treat each molecule as a polarisable site, and use an array of such polarisable dipoles to calculate the electric field and associated energy of any arrangement of charges in the medium. The model incorporates chemical structure via the molecular polarisability and molecular packing patterns via the structure of the array. We use this model to calculate energies of charge pairs undergoing separation in finite fullerene lattices of different chemical and crystal structures. The effective dielectric constants that we estimate from this approach are in good quantitative agreement with those measured experimentally in C60 and phenyl-C61-butyric acid methyl ester (PCBM) films, but we find significant differences in dielectric constant depending on packing and on direction of separation, which we rationalise in terms of density of polarisable fullerene cages in regions of high field. In general, we find lattices containing molecules of more isotropic polarisability tensors exhibit higher dielectric constants. By exploring several model systems we conclude that differences in molecular polarisability (and therefore, chemical structure) appear to be less important than differences in molecular packing and separation direction in determining the energetic landscape for charge separation. We note that the results are relevant for finite lattices, but not necessarily for infinite systems. We propose that the model could be used to design molecular systems for effective electronic screening.
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Journal articleBrandt JR, Salerno F, Fuchter MJ, 2017,
The added value of small-molecule chirality in technological applications
, Nature Reviews Chemistry, Vol: 1, ISSN: 2397-3358Chirality is a fundamental symmetry property; chiral objects, such as chiral small molecules, exist as a pair of non-superimposable mirror images. Although small-molecule chirality is routinely considered in biologically focused application areas (such as drug discovery and chemical biology), other areas of scientific development have not considered small-molecule chirality to be central to their approach. In this Review, we highlight recent research in which chirality has enabled advancement in technological applications. We showcase examples in which the presence of small-molecule chirality is exploited in ways beyond the simple interaction of two different chiral molecules; this can enable the detection and emission of chiral light, help to control molecular motion, or provide a means to control electron spin and bulk charge transport. Thus, we demonstrate that small-molecule chirality is a highly promising avenue for a wide range of technologically oriented scientific endeavours.
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Journal articleWheeler SGM, Bryant D, Troughton J, et al., 2017,
Transient optoelectronic analysis of the impact of material energetics and recombination kinetics on the open-circuit voltage of hybrid perovskite solar cells
, Journal of Physical Chemistry C, Vol: 121, Pages: 13496-13506, ISSN: 1932-7455Transient optoelectronic measurements were used to evaluate the factors determining the open-circuit voltage of a series of planar photovoltaic devices based on hybrid perovskite layers with varying iodine/bromine ratios. Employing differential charging and transient photovoltage measurements, we used a simple device model based on the charge-carrier-density dependence of nongeminate recombination to re-create correctly not only the measured device open-circuit voltage (VOC) as a function of light intensity but also its dependence on bromine substitution. The 173 (±7) mV increase in device voltage observed with 20% bromine substitution is shown to result from a 227 (±8) mV increase in effective electronic band gap, which was offset in part by a 56 (±5) mV voltage loss due to faster carrier recombination. The faster recombination following 20% bromine substitution can be avoided by indene–C60 bisadduct (ICBA) substitution into the [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) electron-collection layer, resulting in a further 73 (±7) mV increase in device VOC. These results are consistent with surface recombination losses at the perovskite/fullerene interface being the primary limitation on the VOC output of bromine-substituted devices. This study thus presents, and experimentally validates, a simple model for the device physics underlying voltage generation in such perovskite-based solar cells and demonstrates that this approach can provide key insights into factors limiting this voltage output as a function of material energetics.
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Journal articleSteiner F, Poelking C, Niedzialek D, et al., 2017,
Influence of orientation mismatch on charge transport across grain boundaries in tri-isopropylsilylethynyl (TIPS) pentacene thin films
, Physical Chemistry Chemical Physics, Vol: 19, Pages: 10854-10862, ISSN: 1463-9076We present a multi-scale model for charge transport across grain boundaries in molecular electronic materials that incorporates packing disorder, electrostatic and polarisation effects. We choose quasi two-dimensional films of tri-isopropylsilylethynyl pentacene (TIPS-P) as a model system representative of technologically relevant crystalline organic semiconductors. We use atomistic molecular dynamics, with a force-field specific for TIPS-P, to generate and equilibrate polycrystalline two-dimensional thin films. The energy landscape is obtained by calculating contributions from electrostatic interactions and polarization. The variation in these contributions leads to energetic barriers between grains. Subsequently, charge transport is simulated using a kinetic Monte-Carlo algorithm. Two-grain systems with varied mutual orientation are studied. We find relatively little effect of long grain boundaries due to the presence of low impedance pathways. However, effects could be more pronounced for systems with limited inter-grain contact areas. Furthermore, we present a lattice model to generalize the model for small molecular systems. In the general case, depending on molecular architecture and packing, grain boundaries can result in interfacial energy barriers, traps or a combination of both with qualitatively different effects on charge transport.
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Journal articleBright JM, Babacan O, Kleissl J, et al., 2017,
A synthetic, spatially decorrelating solar irradiance generator and application to a LV grid model with high PV penetration
, SOLAR ENERGY, Vol: 147, Pages: 83-98, ISSN: 0038-092X -
Journal articleRohr J, Nelson J, Kirchartz T, 2017,
On the correct interpretation of the low voltage region in intrinsic single-carrier devices
, Journal of Physics: Condensed Matter -
Journal articleBabacan O, Torre W, Kleissl J, 2017,
Siting and sizing of distributed energy storage to mitigate voltage impact by solar PV in distribution systems
, SOLAR ENERGY, Vol: 146, Pages: 199-208, ISSN: 0038-092X -
Journal articleBaran D, Tuladhar S, Economopoulos SP, et al., 2017,
Photovoltaic limitations of BODIPY:fullerene based bulk heterojunction solar cells
, SYNTHETIC METALS, Vol: 226, Pages: 25-30, ISSN: 0379-6779 -
Journal articleHermerschmidt F, Savva A, Georgiou E, et al., 2017,
Influence of the Hole Transporting Layer on the Thermal Stability of Inverted Organic Photovoltaics Using Accelerated-Heat Lifetime Protocols
, ACS APPLIED MATERIALS & INTERFACES, Vol: 9, Pages: 14136-14144, ISSN: 1944-8244 -
Journal articleKumar N, Zoladek-Lemanczyk A, Guilbert AAY, et al., 2017,
Simultaneous topographical, electrical and optical microscopy of optoelectronic devices at the nanoscale
, Nanoscale, Vol: 9, Pages: 2723-2731, ISSN: 2040-3364Novel optoelectronic devices rely on complex nanomaterial systems where the nanoscale morphology and local chemical composition are critical to performance. However, the lack of analytical techniques that can directly probe these structure–property relationships at the nanoscale presents a major obstacle to device development. In this work, we present a novel method for non-destructive, simultaneous mapping of the morphology, chemical composition and photoelectrical properties with <20 nm spatial resolution by combining plasmonic optical signal enhancement with electrical-mode scanning probe microscopy. We demonstrate that this combined approach offers subsurface sensitivity that can be exploited to provide molecular information with a nanoscale resolution in all three spatial dimensions. By applying the technique to an organic solar cell device, we show that the inferred surface and subsurface composition distribution correlates strongly with the local photocurrent generation and explains macroscopic device performance. For instance, the direct measurement of fullerene phase purity can distinguish between high purity aggregates that lead to poor performance and lower purity aggregates (fullerene intercalated with polymer) that result in strong photocurrent generation and collection. We show that the reliable determination of the structure–property relationship at the nanoscale can remove ambiguity from macroscopic device data and support the identification of the best routes for device optimisation. The multi-parameter measurement approach demonstrated herein is expected to play a significant role in guiding the rational design of nanomaterial-based optoelectronic devices, by opening a new realm of possibilities for advanced investigation via the combination of nanoscale optical spectroscopy with a whole range of scanning probe microscopy modes.
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Journal articleCalado P, Telford AM, Bryant D, et al., 2016,
Evidence for ion migration in hybrid perovskite solar cells with minimal hysteresis
, Nature Communications, Vol: 7, ISSN: 2041-1723Ionic migration has been proposed as a possible cause of photovoltaic current-voltage hysteresis in hybrid perovskite solar cells. A major objection to this hypothesis is that hysteresis can be reduced by changing the interfacial contact materials; this is unlikely to significantly influence the behaviour of mobile ionic charge within the perovskite phase. Here we show that the primary effects of ionic migration can in fact be observed regardless of whether the contacts were changed to give devices with or without significant hysteresis. Transient optoelectronic measurements combined with device simulations indicate that electric-field screening, consistent with ionic migration, is similar in both high and low hysteresis CH3NH3PbI3 cells. Simulation of the photovoltage and photocurrent transients shows that hysteresis requires the combination of both mobile ionic charge and recombination near the perovskite-contact interfaces. Passivating contact recombination results in higher photogenerated charge concentrations at forward bias which screen the ionic charge, reducing hysteresis.
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Journal articleBarnes PRF, Vaissier V, Garcia Sakai V, et al., 2016,
How mobile are dye adsorbates and acetonitrile molecules on the surface of TiO2 nanoparticles? A quasi-elastic neutron scattering study
, Scientific Reports, Vol: 6, ISSN: 2045-2322Motions of molecules adsorbed to surfaces may control the rate of charge transport within monolayers in systems such as dye sensitized solar cells. We used quasi-elastic neutron scattering (QENS) to evaluate the possible dynamics of two small dye moieties, isonicotinic acid (INA) and bis-isonicotinic acid (BINA), attached to TiO2 nanoparticles via carboxylate groups. The scattering data indicate that moieties are immobile and do not rotate around the anchoring groups on timescales between around 10 ps and a few ns (corresponding to the instrumental range). This gives an upper limit for the rate at which conformational fluctuations can assist charge transport between anchored molecules. Our observations suggest that if the conformation of larger dye molecules varies with time, it does so on longer timescales and/or in parts of the molecule which are not directly connected to the anchoring group. The QENS measurements also indicate that several layers of acetonitrile solvent molecules are immobilized at the interface with the TiO2 on the measurement time scale, in reasonable agreement with recent classical molecular dynamics results.
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Journal articleLoheeswaran S, Thanihaichelvan M, Ravirajan P, et al., 2016,
Controlling recombination kinetics of hybrid poly-3-hexylthiophene (P3HT)/titanium dioxide solar cells by self-assembled monolayers
, JOURNAL OF MATERIALS SCIENCE-MATERIALS IN ELECTRONICS, Vol: 28, Pages: 4732-4737, ISSN: 0957-4522 -
Journal articleBaran D, Ashraf RS, Hanifi DA, et al., 2016,
Reducing the efficiency-stability-cost gap of organic photovoltaics with highly efficient and stable small molecule acceptor ternary solar cells
, Nature Materials, Vol: 16, Pages: 363-369, ISSN: 1476-4660Technological deployment of organic photovoltaic modules requires improvements in device light-conversion efficiency and stability while keeping material costs low. Here we demonstrate highly efficient and stable solar cells using a ternary approach, wherein two non-fullerene acceptors are combined with both a scalable and affordable donor polymer, poly(3-hexylthiophene) (P3HT), and a high-efficiency, low-bandgap polymer in a single-layer bulk-heterojunction device. The addition of a strongly absorbing small molecule acceptor into a P3HT-based non-fullerene blend increases the device efficiency up to 7.7 ± 0.1% without any solvent additives. The improvement is assigned to changes in microstructure that reduce charge recombination and increase the photovoltage, and to improved light harvesting across the visible region. The stability of P3HT-based devices in ambient conditions is also significantly improved relative to polymer:fullerene devices. Combined with a low-bandgap donor polymer (PBDTTT-EFT, also known as PCE10), the two mixed acceptors also lead to solar cells with 11.0 ± 0.4% efficiency and a high open-circuit voltage of 1.03 ± 0.01 V.
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Journal articleFallon KJ, Wijeyasinghe N, Manley EF, et al., 2016,
Indolo-naphthyridine-6,13-dione Thiophene Building Block for Conjugated Polymer Electronics: Molecular Origin of Ultrahigh n-Type Mobility
, CHEMISTRY OF MATERIALS, Vol: 28, Pages: 8366-8378, ISSN: 0897-4756 -
Journal articleSandwell P, Chambon C, Saraogi A, et al., 2016,
Analysis of energy access and impact of modern energy sources in unelectrified villages in Uttar Pradesh
, Energy for Sustainable Development, Vol: 35, Pages: 67-79, ISSN: 0973-0826Bringingaccesstomodernenergysourcestothepoorestinsocietyisakeygoalofmanypolicymakers,businessesandcharities,butinorder tobea success projects and schemesmust be foundedonaccuratedata. We undertooka survey of energy demand and usage patterns in households in unelectrified villages in Uttar Pradesh, India toassess access to and utilisation of energy sources for lighting and cooking. The times of usage were recordedand analysed and the effect on usage patterns of transitioning from traditional to modern energy sourcesis assessed. We quantify the cost and greenhouse gas emissions of current energy use in order to provide abenchmark of potential mitigation through the use of renewable energy technologies: a typical householdwith kerosene lamps only for lighting spends INR 3243 (US$50.67) and emits 381 kgCO2eqper year; householdswithmoderncookingenergyspend17%morethroughincreasedusage,butemit28%lessgreenhousegasescom-pared to those with traditional stoves only. Cell phone ownership was found to be 50% amongst adults. We usedemographic and utilisation data to construct an hourly demand profile of basic electricity demand extrapolatedto each month of the year, and present an example of aspirational demand assess the impact of desirable appli-ances. A Monte Carlo simulation is used to highlight the daily and seasonal variation in total energy and powerdemand. A hybrid system, with solar power and battery storage meeting daytime demand and higher-capacitydiesel- or biomass-powered generation meeting the remainder during evening peaks and winter months,would satisfy demand most effectively.
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Journal articleMoia D, Szumska A, Vaissier V, et al., 2016,
Interdye Hole Transport Accelerates Recombination in Dye Sensitized Mesoporous Films
, Journal of the American Chemical Society, Vol: 138, Pages: 13197-13206, ISSN: 1520-5126Charge recombination between oxidized dyes attached to mesoporous TiO2 and electrons in the TiO2 was studied in inert electrolytes using transient absorption spectroscopy. Simultaneously, hole transport within the dye monolayers was monitored by transient absorption anisotropy. The rate of recombination decreased when hole transport was inhibited selectively, either by decreasing the dye surface coverage or by changing the electrolyte environment. From Monte Carlo simulations of electron and hole diffusion in a particle, modeled as a cubic structure, we identify the conditions under which hole lifetime depends on the hole diffusion coefficient for the case of normal (disorder free) diffusion. From simulations of transient absorption and transient absorption anisotropy, we find that the rate and the dispersive character of hole transport in the dye monolayer observed spectroscopically can be explained by incomplete coverage and disorder in the monolayer. We show that dispersive transport in the dye monolayer combined with inhomogeneity in the TiO2 surface reactivity can contribute to the observed stretched electron-hole recombination dynamics and electron density dependence of hole lifetimes. Our experimental and computational analysis of lateral processes at interfaces can be applied to investigate and optimize charge transport and recombination in solar energy conversion devices using electrodes functionalized with molecular light absorbers and catalysts.
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Conference paperEkins-Daukes NJ, Sandwell P, Nelson J, et al., 2016,
What does CPV need to achieve in order to succeed?
, 12th International Conference on Concentrator Photovoltaic Systems (CPV), Publisher: American Institute of Physics, ISSN: 0094-243XThe recent and dramatic reduction in flat-plate crystalline silicon (c-Si) technology has changed the competitive land-scape for concentrator PV (CPV) systems. Three system cost targets are considered, €1/Wp corresponding to the system cost of c-Si today, €0.75/Wp corresponding to the likely c-Si cost in 2020 and €0.5/Wp corresponding to a likely lower limit for c-Si in the long term. To compete successfully with c-Si, system efficiency needs to be raised from the present 30% to 40%, suggesting cell efficiencies of 50% and module efficiency of 44%. The module should be manufactured at an area cost below €275/m2 which implies a packaged cell cost of €3/cm2 and module + tracking cost €190/m2.
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Journal articleVella E, Li H, Grégoire P, et al., 2016,
Ultrafast decoherence dynamics govern photocarrier generation efficiencies in polymer solar cells
, Scientific Reports, Vol: 6, ISSN: 2045-2322All-organic-based photovoltaic solar cells have attracted considerable attention because of their lowcostprocessing and short energy payback time. In such systems the primary dissociation of an opticalexcitation into a pair of photocarriers has been recently shown to be extremely rapid and efficient,but the physical reason for this remains unclear. Here, two-dimensional photocurrent excitationspectroscopy, a novel non-linear optical spectroscopy, is used to probe the ultrafast coherent decayof photoexcitations into charge-producing states in a polymer:fullerene based solar cell. The twodimensionalphotocurrent spectra are interpreted by introducing a theoretical model for the descriptionof the coupling of the electronic states of the system to an external environment and to the appliedlaser fields. The experimental data show no cross-peaks in the twodimensional photocurrent spectra, aspredicted by the model for coherence times between the exciton and the photocurrent producing statesof 20fs or less.
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Journal articleSandwell P, Duggan G, Nelson J, et al., 2016,
The environmental impact of lightweight HCPV modules: efficient design and effective deployment
, Progress in Photovoltaics, Vol: 24, Pages: 1458-1472, ISSN: 1099-159XWe present a life cycle analysis of a lightweight design of high concentration photovoltaic module. The materials and processes used in construction are considered to assess the total environmental impact of the module construction in terms of the cumulative energy demand and embodied greenhouse gas emissions, which were found to be 355.3MJ and 27.9 kgCO2eq respectively. We consider six potential deployment locations and the system energy payback times are calculated to be 0.22–0.33 years whilst the greenhouse gas payback times are 0.29–0.88 years. The emission intensities over the life- times of the systems are found to be 6.5–9.8 g CO2eq/kWh, lower than those of other HCPV, PV and CSP technologies in similar locations.
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Journal articleFilip MR, Hillman S, Haghighirad AA, et al., 2016,
Band Gaps of the Lead-Free Halide Double Perovskites Cs<sub>2</sub>BiAgCl<sub>6</sub> and Cs<sub>2</sub>BiAgBr<sub>6</sub> from Theory and Experiment
, JOURNAL OF PHYSICAL CHEMISTRY LETTERS, Vol: 7, Pages: 2579-2585, ISSN: 1948-7185 -
Journal articleVezie M, Few S, Meager I, et al., 2016,
Exploring the origin of high optical absorption in conjugated polymers
, Nature Materials, Vol: 15, Pages: 746-753, ISSN: 1476-4660The 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.
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Journal articleLeguy AM, Goñi AR, Frost JM, et al., 2016,
Dynamic disorder, phonon lifetimes, and the assignment of modes to the vibrational spectra of methylammonium lead halide perovskites
, Physical Chemistry Chemical Physics, Vol: 18, Pages: 27051-27066, ISSN: 1463-9084We present Raman and terahertz absorbance spectra of methylammonium lead halide single crystals (MAPbX3, X = I, Br, Cl) at temperatures between 80 and 370 K. These results show good agreement with density-functional-theory phonon calculations. Comparison of experimental spectra and calculated vibrational modes enables confident assignment of most of the vibrational features between 50 and 3500 cm(-1). Reorientation of the methylammonium cations, unlocked in their cavities at the orthorhombic-to-tetragonal phase transition, plays a key role in shaping the vibrational spectra of the different compounds. Calculations show that these dynamic effects split Raman peaks and create more structure than predicted from the independent harmonic modes. This explains the presence of extra peaks in the experimental spectra that have been a source of confusion in earlier studies. We discuss singular features, in particular the torsional vibration of the C-N axis, which is the only molecular mode that is strongly influenced by the size of the lattice. From analysis of the spectral linewidths, we find that MAPbI3 shows exceptionally short phonon lifetimes, which can be linked to low lattice thermal conductivity. We show that optical rather than acoustic phonon scattering is likely to prevail at room temperature in these materials.
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Journal articleTuladhar SM, Azzouzi M, Delval F, et 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 articleGambhir 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: 0927-0248Organic 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.
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Journal articleGuilbert AA, Zbiri M, Jenart MV, et 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: 1948-7185The 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.
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Journal articleSandwell P, Chan NLA, Foster S, et 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: 0927-0248Over 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.
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Contact
Jenny Nelson
Professor of Physics
1007, Huxley Building
South Kensington, London, SW7 2AZ