Publications
34 results found
Macdonald TJ, Batmunkh M, Lin C-T, et al., 2019, Origin of performance enhancement in TiO2-carbon nanotube composite perovskite solar cells, Small Methods, Vol: 3, Pages: 1-10, ISSN: 2366-9608
Carbon nanotubes are shown to be beneficial additives to perovskite solar cells, and the inclusion of such nanomaterials will continue to play a crucial role in the push toward developing efficient and stable device architectures. Herein, titanium dioxide/carbon nanotube composite perovskite solar cells are fabricated, and device performance parameters are correlated with spectroscopic signatures of the materials to understand the origin of performance enhancement. By probing the charge carrier dynamics with photoluminescence and femtosecond transient absorption spectroscopy, the results indicate that charge transfer is not improved by the presence of the carbon nanotubes. Instead, carbon nanotubes are shown to passivate the electronic defect states within the titanium dioxide, which can lead to stronger radiative recombination in the titanium dioxide/carbon nanotube films. The defect passivation allows the perovskite solar cells made using an optimized titanium dioxide/carbon nanotube composite to achieve a peak power conversion efficiency of 20.4% (19% stabilized), which is one of the highest values reported for perovskite solar cells not incorporating a mixed cation light absorbing layer. The results discuss new fundamental understandings for the role of carbon nanomaterials in perovskite solar cells and present a significant step forward in advancing the field of high‐performance photovoltaics.
Lin C, Pont S, Kim J, et al., 2018, Passivation of oxygen and light induced degradation by the PCBM electron transport layer in planar perovskite solar cells, Sustainable Energy and Fuels, Vol: 2, Pages: 1686-1692, ISSN: 2398-4902
Herein, we investigate the causes of a 20 fold improved stability of inverted, planar structure (ITO/PTAA/CH3NH3PbI3/PCBM/BCP/Cu) compared to conventional structure devices (FTO/compact-TiO2/meso-TiO2/CH3NH3PbI3/spiro-OMeTAD/Au) under oxygen and light stress. The PCBM layer is shown to function as an oxygen diffusion barrier and passivation layer against superoxide mediated degradation. The passivation properties of the PCBM layer are shown to depend on the electron affinity of fullerene acceptor, attributed to low LUMO level of PCBM energetically inhibiting superoxide generation. We also find the planar structure devices shows slower lateral oxygen diffusion rates than mesoporous scaffold devices, with these slower diffusion rates (days per 100 μm) also being a key factor in enhancing stability. Faster degradation is observed under voltage cycling, attributed to oxygen diffusion kinetics being ion motion dependent. We conclude by discussing the implications of these results for the design of perovskite solar cells with improved resistance to oxygen and light induced degradation.
Francas Forcada L, Burns E, Steier L, et al., 2018, Rational design of a neutral pH functional and stable organic photocathode., Chemical Communications, Vol: 2018, ISSN: 1359-7345
In this work we lay out design guidelines for catalytically more efficient organic photocathodes achieving stable hydrogen production in neutral pH. We propose an organic photocathode architecture employing a NiO hole selective layer, a PCDTBT:PCBM bulk heterojunction, a compact TiO2 electron selective contact and a RuO2 nanoparticle catalyst. The role of each layer is discussed in terms of durability and function. With this strategically designed organic photocathode we obtain stable photocurrent densities for over 5 h and discuss routes for further performance improvement.
Godin R, Ma X, González-Carrero S, et al., 2018, Tuning charge carrier dynamics and surface passivation in organolead halide perovskites with capping ligands and metal oxide interfaces, Advanced Optical Materials, Vol: 6, ISSN: 2195-1071
Organolead halide perovskites have emerged as exciting optoelectronic materials but a complete understanding of their photophysical properties is still lacking. Here, a morphological series of methylammonium lead bromide (MAPbBr 3 ) perovskites are studied by transient optical spectroscopies over eight orders of magnitude in timescale to investigate the effect of nanostructuring and surface states on the charge carrier dynamics. The sample preparation route and corresponding morphology changes influence the position of the optical features, recombination dynamics, excitation fluence dependence, and dramatically impact surface trap passivation. Growth of the perovskite layer in the presence of capping ligands or within mesoporous alumina increases the photoluminescence efficiency by multiple orders of magnitude, indicating that interfacing with metal oxides can lead to the passivation of surface nonradiative recombination centers. Nanoparticles (NPs) dispersed in solution show mixed behavior since they consist of NPs on nanoplatelets, while isolated NPs could be grown within mesoporous alumina with the addition of capping ligands. Investigation on the microsecond timescale suggests that an exponential distribution of states below the band edges results in long-lived charges. The investigations of the relationship between sample architecture and charge carrier dynamics will help in the appropriate choice of perovskite morphology for use in optoelectronic devices.
Calado 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: 2041-1723
Ionic 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.
Belisle RA, Nguyen WH, Bowring AR, et al., 2016, Interpretation of inverted photocurrent transients in organic lead halide perovskite solar cells; proof of the field screening by mobile ions and determination of the space charge layer widths, Energy & Environmental Science, Vol: 10, Pages: 192-204, ISSN: 1754-5706
In Methyl Ammonium Lead Iodide (MAPI) perovskite solar cells, screening of the built in field by mobile ions has been proposed as part of the cause of the large hysteresis observed in the current/voltage scans in many cells. We show that photocurrent transients measured immediately (e.g. 100 μs) after a voltage step can provide direct evidence that this field screening exists. Just after a step to forward bias, the photocurrent transients are reversed in sign (i.e. inverted), and the magnitude of the inverted transients can be used to find an upper bound on the width of the space charge layers adjacent to the electrodes. This in turn provides a lower bound on the mobile charge concentration, which we find to be 1 x 1017/cm3. Using a new photocurrent transient experiment, we show that the space charge layer thickness remains approximately constant as a function of bias, as expected for mobile ions in a solid electrolyte. We also discuss additional characteristics of the inverted photocurrent transients that imply either an unusually stable deep trapping, or a photo effect on the mobile ion conductivity.
Barnes 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: 2045-2322
Motions 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.
Brinkert K, Le formal F, Li X, et al., 2016, Photocurrents from photosystem II in a metal oxide hybrid system: electron transfer pathways, Biochimica et Biophysica Acta-Bioenergetics, Vol: 1857, Pages: 1497-1505, ISSN: 0005-2728
We have investigated the nature of the photocurrent generated by Photosystem II (PSII), the water oxidising enzyme, isolated from Thermosynechococcus elongatus, when immobilized on nanostructured titanium dioxide on an indium tin oxide electrode (TiO2/ITO). We investigated the properties of the photocurrent from PSII when immobilized as a monolayer versus multilayers, in the presence and absence of an inhibitor that binds to the site of the exchangeable quinone (QB) and in the presence and absence exogenous mobile electron carriers (mediators). The findings indicate that electron transfer occurs from the first quinone (QA) directly to the electrode surface but that the electron transfer through the nanostructured metal oxide is the rate-limiting step. Redox mediators enhance the photocurrent by taking electrons from the nanostructured semiconductor surface to the ITO electrode surface not from PSII. This is demonstrated by photocurrent enhancement using a mediator incapable of accepting electrons from PSII. This model for electron transfer also explains anomalies reported in the literature using similar and related systems. The slow rate of the electron transfer step in the TiO2 is due to the energy level of electron injection into the semiconducting material being below the conduction band. This limits the usefulness of the present hybrid electrode. Strategies to overcome this kinetic limitation are discussed.
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
Leguy AMA, Frost JM, McMahon AP, et al., 2015, Corrigendum: The dynamics of methylammonium ions in hybrid organic–inorganic perovskite solar cells, Nature Communications, Vol: 6, ISSN: 2041-1723
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.
Wang X, Kafizas A, Li X, et al., 2015, Transient Absorption Spectroscopy of Anatase and Rutile: The Impact of Morphology and Phase on Photocatalytic Activity, JOURNAL OF PHYSICAL CHEMISTRY C, Vol: 119, Pages: 10439-10447, ISSN: 1932-7447
- Author Web Link
- Open Access Link
- Cite
- Citations: 122
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
Neri G, Walsh JJ, Wilson C, et al., 2015, A functionalised nickel cyclam catalyst for CO<sub>2</sub> reduction: electrocatalysis, semiconductor surface immobilisation and light-driven electron transfer, PHYSICAL CHEMISTRY CHEMICAL PHYSICS, Vol: 17, Pages: 1562-1566, ISSN: 1463-9076
- Author Web Link
- Cite
- Citations: 55
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
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
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
Barnes PRF, Miettunen K, Li X, et al., 2013, Interpretation of optoelectronic transient and charge extraction measurements in dye sensitised solar cells, Advanced Materials
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
O'Regan B, Li X, Ghaddar T, 2012, Dye adsorption, desorption, and distribution in mesoporous TiO<sub>2</sub> films, and its effects on recombination losses in dye sensitized solar cells, ENERGY & ENVIRONMENTAL SCIENCE, Vol: 5, Pages: 7203-7215, ISSN: 1754-5692
- Author Web Link
- Cite
- Citations: 107
Xiaoe Li, Anna Reynal, Piers R F Barnes, et al., 2012, Measured binding coefficients for iodine and ruthenium dyes; implications for recombination in dye sensitised solar cells, Physical Chemistry Chemical Physics
Yamazaki M, Hofmann O, Ryu G, et al., 2011, Non-emissive colour filters for fluorescence detection, LAB ON A CHIP, Vol: 11, Pages: 1228-1233, ISSN: 1473-0197
- Author Web Link
- Cite
- Citations: 15
Li X, Nazeeruddin MK, Thelakkat M, et al., 2011, Spectroelectrochemical studies of hole percolation on functionalised nanocrystalline TiO<sub>2</sub> films: a comparison of two different ruthenium complexes, PHYSICAL CHEMISTRY CHEMICAL PHYSICS, Vol: 13, Pages: 1575-1584, ISSN: 1463-9076
- Author Web Link
- Cite
- Citations: 32
Barnes PRF, Anderson AY, Juozapavicius M, et al., 2011, Factors controlling charge recombination under dark and light conditions in dye sensitised solar cells, PHYSICAL CHEMISTRY CHEMICAL PHYSICS, Vol: 13, Pages: 3547-3558, ISSN: 1463-9076
- Author Web Link
- Cite
- Citations: 62
Law C, Pathirana SC, Li X, et al., 2010, Water-Based Electrolytes for Dye-Sensitized Solar Cells, ADVANCED MATERIALS, Vol: 22, Pages: 4505-4509, ISSN: 0935-9648
- Author Web Link
- Cite
- Citations: 138
Benedetti JE, Goncalves AD, Formiga ALB, et al., 2010, A polymer gel electrolyte composed of a poly(ethylene oxide) copolymer and the influence of its composition on the dynamics and performance of dye-sensitized solar cells, JOURNAL OF POWER SOURCES, Vol: 195, Pages: 1246-1255, ISSN: 0378-7753
- Author Web Link
- Cite
- Citations: 76
Barnes PRF, Liu L, Li X, et al., 2009, Re-evaluation of Recombination Losses in Dye-Sensitized Cells: The Failure of Dynamic Relaxation Methods to Correctly Predict Diffusion Length in Nanoporous Photoelectrodes, NANO LETTERS, Vol: 9, Pages: 3532-3538, ISSN: 1530-6984
- Author Web Link
- Cite
- Citations: 84
Kemp GL, Marritt SJ, Li X, et al., 2009, Opportunities for mesoporous nanocrystalline SnO<sub>2</sub> electrodes in kinetic and catalytic analyses of redox proteins, BIOCHEMICAL SOCIETY TRANSACTIONS, Vol: 37, Pages: 368-372, ISSN: 0300-5127
- Author Web Link
- Cite
- Citations: 23
Gimeno N, Li X, Durrant JR, et al., 2008, Cyanide sensing with organic dyes:: Studies in solution and on nanostructured Al<sub>2</sub>O<sub>3</sub> surfaces, CHEMISTRY-A EUROPEAN JOURNAL, Vol: 14, Pages: 3006-3012, ISSN: 0947-6539
- Author Web Link
- Cite
- Citations: 175
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.