Publications
105 results found
Moia D, Cappel UB, Leijtens T, et 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
Bryant D, Wheeler S, ORegan BC, et al., 2015, Observable Hysteresis at Low Temperature in “Hysteresis Free” Organic–Inorganic Lead Halide Perovskite Solar Cells, The Journal of Physical Chemistry Letters, Vol: 6, Pages: 3190-3194, ISSN: 1948-7185
Eames C, Frost JM, Barnes PRF, et al., 2015, Ionic transport in hybrid lead iodide perovskite solar cells, Nature Communications, Vol: 6, ISSN: 2041-1723
Solar cells based on organic–inorganic halide perovskites have recently shown rapidly rising power conversion efficiencies, but exhibit unusual behaviour such as current–voltage hysteresis and a low-frequency giant dielectric response. Ionic transport has been suggested to be an important factor contributing to these effects; however, the chemical origin of this transport and the mobile species are unclear. Here, the activation energies for ionic migration in methylammonium lead iodide (CH3NH3PbI3) are derived from first principles, and are compared with kinetic data extracted from the current–voltage response of a perovskite-based solar cell. We identify the microscopic transport mechanisms, and find facile vacancy-assisted migration of iodide ions with an activation energy of 0.6 eV, in good agreement with the kinetic measurements. The results of this combined computational and experimental study suggest that hybrid halide perovskites are mixed ionic–electronic conductors, a finding that has major implications for solar cell device architectures.
Leguy AMA, Frost JM, McMahon AP, et 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.
Leguy AMA, Hu Y, Campoy-Quiles M, et 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.
O'Regan BC, Barnes PRF, Li X, et al., 2015, Optoelectronic Studies of Methylammonium Lead Iodide Perovskite Solar Cells with Mesoporous TiO<sub>2</sub>: Separation of Electronic and Chemical Charge Storage, Understanding Two Recombination Lifetimes, and the Evolution of Band Offsets during <i>J</i>-<i>V</i> Hysteresis, JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, Vol: 137, Pages: 5087-5099, ISSN: 0002-7863
- Author Web Link
- Open Access Link
- Cite
- Citations: 231
Carnie MJ, Troughton J, Regan BO, et al., 2015, Identifying Recombination Mechanisms Through Materials Development In Perovskite Solar Cells, IEEE 42nd Photovoltaic Specialist Conference (PVSC), Publisher: IEEE, ISSN: 0160-8371
- Author Web Link
- Cite
- Citations: 1
Manke F, Frost JM, Vaissier V, et 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
- Author Web Link
- Open Access Link
- Cite
- Citations: 12
Law C, Miseikis L, Dimitrov S, et al., 2014, Performance and Stability of Lead Perovskite/TiO<sub>2</sub>, Polymer/PCBM, and Dye Sensitized Solar Cells at Light Intensities up to 70 Suns, ADVANCED MATERIALS, Vol: 26, Pages: 6268-6273, ISSN: 0935-9648
- Author Web Link
- Cite
- Citations: 94
Vaissier V, Mosconi E, Moia D, et al., 2014, Effect of Molecular Fluctuations on Hole Diffusion within Dye Monolayers, CHEMISTRY OF MATERIALS, Vol: 26, Pages: 4731-4740, ISSN: 0897-4756
- Author Web Link
- Cite
- Citations: 21
Edri E, Kedem N, Cohen H, et al., 2014, Higher Open Circuit Voltage and Reduced UV-Induced Reverse Current in ZnO-Based Solar Cells by a Chemically Modified Blocking Layer, JOURNAL OF PHYSICAL CHEMISTRY C, Vol: 118, Pages: 16884-16891, ISSN: 1932-7447
- Author Web Link
- Cite
- Citations: 12
Jeanbourquin XA, Li X, Law C, et al., 2014, Rediscovering a Key Interface in Dye-Sensitized Solar Cells: Guanidinium and Iodine Competition for Binding Sites at the Dye/Electrolyte Surface, JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, Vol: 136, Pages: 7286-7294, ISSN: 0002-7863
- Author Web Link
- Cite
- Citations: 39
Jiang R, Anderson A, Barnes PRF, et al., 2014, 2000 hours photostability testing of dye sensitised solar cells using a cobalt bipyridine electrolyte, JOURNAL OF MATERIALS CHEMISTRY A, Vol: 2, Pages: 4751-4757, ISSN: 2050-7488
Enrique Galvez F, Barnes PRF, Halme J, et al., 2014, Dye sensitized solar cells as optically random photovoltaic media, ENERGY & ENVIRONMENTAL SCIENCE, Vol: 7, Pages: 689-697, ISSN: 1754-5692
- Author Web Link
- Cite
- Citations: 30
Moia D, Vaissier V, Lopez-Duarte I, et al., 2014, The reorganization energy of intermolecular hole hopping between dyes anchored to surfaces, CHEMICAL SCIENCE, Vol: 5, Pages: 281-290, ISSN: 2041-6520
- Author Web Link
- Cite
- Citations: 59
Vaissier V, Barnes PRF, Kirkpatrick J, et al., 2013, Influence of polar medium on the reorganization energy of charge transfer between dyes in a dye sensitized film, Physical Chemistry Chemical Physics, Vol: 15, Pages: 4804-4814
We study the kinetics of the lateral hole transfer occurring between dye molecules anchored at the surface of the metal oxide in Dye Sensitized Solar Cells (DSSC). We use Marcus' charge transfer rate equation for which we need the electronic coupling between two molecules (J) and the reorganization energy (λtot). In DSSC the medium surrounding the dyes is highly polar. This means that the contribution of the solvent to the reorganization energy cannot be neglected. Here we elaborate a method to calculate, from first principles, the total (i.e., inner- and outer-sphere) reorganization energy of hole exchange between ruthenium dyes. The influence of the solvent and of the ions in the solvent is incorporated. The inner-sphere reorganization energy depends on the nature of the dye, 0.1 eV for ruthenium dyes with CN ligands, 0.2 eV for ruthenium dyes with NCS ligands. In acetonitrile, the solvent reorganization energy contributes for at least 80% of the total giving a total reorganization energy of around 0.86 eV for ruthenium dyes with CN ligands and 0.95 eV for ruthenium dyes with NCS ligands. We use these results to estimate the rate of hole transfer within Marcus theory. We suggest that low diffusion coefficients observed experimentally may arise from the high polarity of the medium rather than by the chemical structure of the dye.
Barnes PRF, Miettunen K, Li X, et al., 2013, Interpretation of optoelectronic transient and charge extraction measurements in dye sensitised solar cells, Advanced Materials
Vaissier V, Barnes P, Kirkpatrick J, et al., 2013, Influence of polar medium on the reorganization energy of charge transfer between dyes in a dye sensitized film, PHYSICAL CHEMISTRY CHEMICAL PHYSICS, Vol: 15, Pages: 4804-4814, ISSN: 1463-9076
- Author Web Link
- Cite
- Citations: 75
Cowan AJ, Leng W, Barnes PRF, et al., 2013, Charge carrier separation in nanostructured TiO<sub>2</sub> photoelectrodes for water splitting, PHYSICAL CHEMISTRY CHEMICAL PHYSICS, Vol: 15, Pages: 8772-8778, ISSN: 1463-9076
- Author Web Link
- Cite
- Citations: 58
Miettunen K, Saukkonen T, Li X, et al., 2013, Do Counter Electrodes on Metal Substrates Work with Cobalt Complex Based Electrolyte in Dye Sensitized Solar Cells?, JOURNAL OF THE ELECTROCHEMICAL SOCIETY, Vol: 160, Pages: H132-H137, ISSN: 0013-4651
- Author Web Link
- Cite
- Citations: 29
Juozapavicius M, Kaucikas M, Dimitrov SD, et al., 2013, Evidence for “Slow” Electron Injection in Commercially Relevant Dye-2 Sensitized Solar Cells by Vis−NIR and IR Pump−Probe Spectroscopy, J Phys Chem C
We present femtosecond to nanosecond transient absorption (TA)data on electron injection in dye-sensitized solar cells (DSSCs) fabricated with lowvolatility, commercially relevant electrolytes, with and without added lithium.Results are shown over an extended time range (300 fs−6.3 ns) and extendedwavelength range (800−1400 nm) for both N719 and C106 dyes. Kinetics weremeasured on both TiO2 and noninjecting ZrO2. Using the latter, we havedetermined the spectra and absorption coefficient of N719* across the wavelengthrange. We find an isosbestic point in the TA spectra on TiO2 near 900 nm for allcells, existing from <1 ps to >1 ns. We show how measurements near this isosbesticpoint can give a false impression of uniformly femtosecond injection dynamics inDSSCs. Comparison of dynamics measured at 1200 nm with mid-IR transient absorption measured at 5100 nm confirms amajority proportion of slow (>10 ps) electron injection in these commercially relevant cells. We also comment on a recentpublication which appears to directly contradict the results we present.
Li X, Reynal A, Barnes PRF, et al., 2012, Measured binding coefficients for iodine and ruthenium dyes; implications for recombination in dye sensitised solar cells, Physical Chemistry Chemical Physics, Vol: 14, Pages: 15421-15428
We have measured the binding coefficients of iodine to three dyes used in Dye Sensitised Solar Cells (DSSCs). Binding coefficients are quantified via the effect of iodine binding on the UV-vis spectrum of the dye. From iodine titration curves of dye sensitised TiO2 films we find that the binding coefficients of iodine to the dyes C101, N719 and AR24 (vide infra) are in the range of 2000–4000 M−1. From FTIR results and molecular modelling we show the iodine binds to the thiocyanate group in all these dyes. For the AR24 dye we present evidence that iodine also binds to the amine moiety on this dye. With these binding coefficients we show that the dye–iodine complex will be present at much higher concentrations than free iodine in the pore structure of a DSSC. As we have recently shown that iodine (rather than tri-iodide) is the dominant acceptor in electron recombination, the concentration dye–iodine complexes could influence recombination rates and thus Voc. By comparison of recombination data on full cells, we show that AR24 accelerates recombination by a factor of 7 over N719, presumably due to the iodine binding to the amine group. We leave open the question why iodine binding to the amine group seems to have a stronger effect on the recombination than does binding to the thiocyanate.
Carnie MJ, Charbonneau C, Barnes PRF, et al., 2012, Ultra-fast sintered TiO2 films in dye-sensitized solar cells: phase variation, electron transport and recombination, Journal of Materials Chemistry A, Vol: 1, Pages: 2225-2230
With the application of near-infrared radiation (NIR), TiO2 films for dye-sensitized solar cells (DSCs) on metallic substrates can be sintered in just 12.5 seconds. The photovoltaic performance of devices made with NIR sintered films match those devices made with conventionally sintered films prepared by heating for 1800 seconds. Here we characterise the electron transport, electron lifetime and phase-morphological properties of ultrafast NIR sintered films, using impedance spectroscopy, transient photovoltage decay and X-ray diffraction measurements. An important factor in NIR processing of TiO2 films is the peak metal temperature (PMT) and we show that during the 12.5 second heat treatment, a PMT of around 635 °C gives near identical electron transport, electron lifetime and morphological properties, as well comparable photovoltaic performance to a conventionally sintered (500 °C, 30 min) film. We demonstrate that the rapid heating of the TiO2 (to temperatures of up to 785 °C) does not lead to a large scale rutile phase transition. As such photovoltaic performance of resultant DSC devices is maintained since the heating period is insufficient to induce a significant transition from anatase to rutile or morphology changes which result in a loss of photocurrent.
Barnes P, 2012, Understanding nanostructured solar cells using optical and optoelectronic transient techniques
Barnes P, 2012, Understanding nanostructured solar cells using optical and optoelectronic transient techniques
Efficiencies of 12 % have recently been achieved using dye sensitised and semiconductor sensitised solar cells. I will describe the developments as well as the transient absorption and optoelectronic techniques that are used to understand and improve the performance of these devices. Biography: Piers Barnes holds an EPSRC Career Acceleration Fellowship at Imperial College London. His group is investigating charge carrier dynamics and molecular wiring in hybrid optoelectronic devices such as dye sensitised solar cells (DSSCs). Piers received an MSci in Physics from Bristol University and undertook his PhD studies with the British Antarctic Survey where he helped recover and analyse the world's oldest ice core. This was followed by a postdoctoral fellowship with the CSIRO in Australia (2004- 2007), working on photoelectrochemical water splitting. His activities involved the fabrication, measurement and simulation of metal oxide photoelectrodes, focused on TiO2, ZnO, WO3 and Fe2O3 and the accurate measurement of efficiency. He returned to the UK for a postdoc in the Chemistry Department at Imperial to work on understanding loss mechanisms in DSSCs before starting his fellowship in the Physics Department. © OSA 2012.
Barnes P, 2012, Understanding nanostructured solar cells using optical and optoelectronic transient techniques
Barnes P, 2012, Understanding nanostructured solar cells using optical and optoelectronic transient techniques
Efficiencies of 12 % have recently been achieved using dye sensitised and semiconductor sensitised solar cells. I will describe the developments as well as the transient absorption and optoelectronic techniques that are used to understand and improve the performance of these devices. © OSA 2012.
Barnes P, 2012, Understanding nanostructured solar cells using optical and optoelectronic transient techniques
Miettunen K, Barnes PRF, Li X, et al., 2012, The effect of electrolyte filling method on the performance of dye-sensitized solar cells, JOURNAL OF ELECTROANALYTICAL CHEMISTRY, Vol: 677, Pages: 41-49, ISSN: 1572-6657
- Author Web Link
- Cite
- Citations: 14
Barnes P, 2012, Understanding nanostructured solar cells using optical and optoelectronic transient techniques
Efficiencies of 12 % have recently been achieved using dye sensitised and semiconductor sensitised solar cells. I will describe the developments as well as the transient absorption and optoelectronic techniques that are used to understand and improve the performance of these devices. © OSA 2012.
This data is extracted from the Web of Science and reproduced under a licence from Thomson Reuters. You may not copy or re-distribute this data in whole or in part without the written consent of the Science business of Thomson Reuters.