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  • Journal article
    Corby S, Rao R, Steier L, Durrant Jet al., 2021,

    The kinetics of metal oxide photoanodesfrom charge generation to catalysis

    , Nature Reviews Materials, Vol: 6, Pages: 1136-1155, ISSN: 2058-8437

    Generating charge carriers with lifetimes long enough to drive catalysis is a critical aspect for both photoelectrochemical and photocatalytic systems and a key determinant of their efficiency. This review addresses the charge carrier dynamics underlying the performance of metal oxides as photoanodes and their ability to drive photoelectrochemical water oxidation, alongside wider comparison with metal oxide function in photocatalytic and electrocatalytic systems. We start by highlighting the disparity between the ps–ns lifetimes of electron and holes photoexcited in bulk metal oxides versus the ms –s timescale of water oxidation catalysis. We go onto review recent literature of the dominant kinetic processes determining photoanode performance, namely charge generation, polaron formation and charge trapping, bulk and surface recombination, charge separation and extraction, and finally the kinetics of water oxidation catalysis. With each topic, we review current understanding and note areas of remaining uncertainty or controversy. We discuss the potential for material selection and examine approaches such as doping, nanostructuring, junction formation and/or co-catalyst deposition to enhance performance. Critically, we examine how such performance enhancements can be understood from analyses of carrier dynamics and propose design guidelines for further material or device optimisation.

  • Journal article
    Dong Y, Cha H, Bristow H, Lee J, Kumar A, McCulloch I, Bakulin A, Durrant Jet al., 2021,

    Correlating charge-transfer state lifetimes with material ener-getics in polymer:non-fullerene acceptor organic solar cells

    , Journal of the American Chemical Society, Vol: 143, Pages: 7599-7603, ISSN: 0002-7863

    Minimizing the energy offset between the lowest exciton and charge-transfer (CT) states is a widely employed strategy to suppress the energy loss (Eg/q – VOC) in polymer:non-fullerene acceptor (NFA) organic solar cells (OSCs). In this work, transient absorption spectroscopy is employed to determine CT state lifetimes in a series of low energy loss polymer:NFA blends. The CT state lifetime is observed to show an inverse energy gap law dependence and decreases as the energy loss is reduced. This behavior is assigned to increased mixing/hybridization between these CT states and shorter-lived singlet excitons of the lower gap component as the energy offset ΔECT-S1 is reduced. This study highlights how achieving longer exciton and CT state lifetimes has the potential for further enhancement of OSC efficiencies.

  • Journal article
    Bucci A, Garcia-Tecedor M, Corby S, Rao RR, Martin-Diaconescu V, Oropeza FE, de la Pena O'Shea VA, Durrant JR, Gimenez S, Lloret-Fillol Jet al., 2021,

    Self-supported ultra-active NiO-based electrocatalysts for the oxygen evolution reaction by solution combustion

    , JOURNAL OF MATERIALS CHEMISTRY A, Vol: 9, Pages: 12700-12710, ISSN: 2050-7488
  • Journal article
    Limbu S, Park K-B, Wu J, Cha H, Yun S, Lim S-J, Yan H, Luke J, Ryu G, Heo C-J, Kim S, Jin YW, Durrant JR, Kim J-Set al., 2021,

    Identifying the Molecular Origins of High-Performance in Organic Photodetectors Based on Highly Intermixed Bulk Heterojunction Blends

    , ACS NANO, Vol: 15, Pages: 1217-1228, ISSN: 1936-0851
  • Journal article
    Tian L, Tyburski R, Wen C, Sun R, Abdellah M, Huang J, DAmario L, Boschloo G, Hammarström L, Tian Het al., 2020,

    Understanding the Role of Surface States on Mesoporous NiO Films

    , Journal of the American Chemical Society, Vol: 142, Pages: 18668-18678, ISSN: 0002-7863
  • Journal article
    Mesa CA, Steier L, Moss B, Francas L, Thorne JE, Grätzel M, Durrant JRet al., 2020,

    Impact of synthesis route on the water oxidation kinetics of hematite photoanodes

    , The Journal of Physical Chemistry Letters, Vol: 11, Pages: 7285-7290, ISSN: 1948-7185

    Operando spectroelectrochemical analysis is used to determine the water oxidation reaction kinetics for hematite photoanodes prepared using four different synthetic procedures. Whilst these photoanodes exhibit very different current / voltage performance, their underlying water oxidation kinetics are found to be almost invariant. Higher temperature thermal annealing was found to correlate with a shift in the photocurrent onset potential towards less positive potentials, assigned to a suppression of both back electron-hole recombination and of charge accumulation in intraband-gap states, indicating these intraband-gap states do not contribute directly to water oxidation.

  • Journal article
    Windle CD, Wieczorek A, Xiong L, Sachs M, Bozal-Ginesta C, Cha H, Cockcroft JK, Durrant J, Tang Jet al., 2020,

    Covalent grafting of molecular catalysts on C(3)N(x)H(y)as robust, efficient and well-defined photocatalysts for solar fuel synthesis

    , CHEMICAL SCIENCE, Vol: 11, Pages: 8425-8432, ISSN: 2041-6520
  • Journal article
    Lee J, Cha H, Yao H, Hou J, Suh Y-H, Jeong S, Lee K, Durrant JRet al., 2020,

    Toward Visibly Transparent Organic Photovoltaic Cells Based on a Near-Infrared Harvesting Bulk Heterojunction Blend

    , ACS APPLIED MATERIALS & INTERFACES, Vol: 12, Pages: 32764-32770, ISSN: 1944-8244
  • Journal article
    Cha H, Zheng Y, Dong Y, Lee HH, Wu J, Bristow H, Zhang J, Lee HKH, Tsoi WC, Bakulin AA, McCulloch I, Durrant JRet al., 2020,

    Exciton and charge carrier dynamics in highly crystalline PTQ10:IDIC organic solar cells

    , Advanced Energy Materials, Pages: 1-11, ISSN: 1614-6832

    Herein the morphology and exciton/charge carrier dynamics in bulk heterojunctions (BHJs) of the donor polymer PTQ10 and molecular acceptor IDIC are investigated. PTQ10:IDIC BHJs are shown to be particularly promising for low cost organic solar cells (OSCs). It is found that both PTQ10 and IDIC show remarkably high crystallinity in optimized BHJs, with GIWAXS data indicating pi‐pi stacking coherence lengths of up to 8 nm. Exciton‐exciton annihilation studies indicate long exciton diffusion lengths for both neat materials (19 nm for PTQ10 and 9.5 nm for IDIC), enabling efficient exciton separation with half lives of 1 and 3 ps, despite the high degree of phase segregation in this blend. Transient absorption data indicate exciton separation leads to the formation of two spectrally distinct species, assigned to interfacial charge transfer (CT) states and separated charges. CT state decay is correlated with the appearance of additional separate charges, indicating relatively efficient CT state dissociation, attributed to the high crystallinity of this blend. The results emphasize the potential for high material crystallinity to enhance charge separation and collection in OSCs, but also that long exciton diffusion lengths are likely to be essential for efficient exciton separation in such high crystallinity devices.

  • Journal article
    Wu J, Lee J, Chin Y-C, Yao H, Cha H, Luke J, Hou J, Kim J-S, Durrant Jet al., 2020,

    Exceptionally low charge trapping enables highly efficient organic bulk heterojunction solar cells

    , Energy & Environmental Science, Vol: 13, Pages: 2422-2430, ISSN: 1754-5692

    In this study, we investigate the underlying origin of the high performance of PM6:Y6 organic solar cells. Employing transient optoelectronic and photoemission spectroscopies, we find that this blend exhibits greatly suppressed charge trapping into electronic intra-bandgap tail states compared to other polymer/non-fullerene acceptor solar cells, attributed to lower energetic disorder. The presence of tail states is a key source of energetic loss in most organic solar cells, as charge carriers relax into these states, reducing the quasi-Fermi level splitting and therefore device VOC. DFT and Raman analyses indicate this suppression of tail state energetics disorder could be associated with a higher degree of conformational rigidity and uniformity for the Y6 acceptor. We attribute the origin of such conformational rigidity and uniformity of Y6 to the presence of the two alkyl side chains on the outer core that restricts end-group rotation by acting as a conformation locker. The resultant enhanced carrier dynamics and suppressed charge carrier trapping are proposed to be a key factor behind the high performance of this blend. Low energetic disorder is suggested to be a key factor enabling reasonably efficient charge generation in this low energy offset system. In the absence of either energetic disorder or a significant electronic energy offset, it is argued that charge separation in this system is primarily entropy driven. Nevertheless, photocurrent generation is still limited by slow hole transfer from Y6 to PM6, suggesting pathways for further efficiency improvement.

  • Journal article
    Lin Y-H, Sakai N, Da P, Wu J, Sansom HC, Ramadan AJ, Mahesh S, Liu J, Oliver RDJ, Lim J, Aspitarte L, Sharma K, Madhu PK, Morales-Vilches AB, Nayak PK, Bai S, Gao F, Grovenor CRM, Johnston MB, Labram JG, Durrant JR, Ball JM, Wenger B, Stannowski B, Snaith HJet al., 2020,

    A piperidinium salt stabilizes efficient metal-halide perovskite solar cells

    , Science, Vol: 369, Pages: 1-7, ISSN: 0036-8075

    Longevity has been a long-standing concern for hybrid perovskite photovoltaics. We demonstrate high-resilience positive-intrinsic-negative perovskite solar cells by incorporating a piperidinium-based ionic compound into the formamidinium-cesium lead-trihalide perovskite absorber. With the bandgap tuned to be well suited for perovskite-on-silicon tandem cells, this piperidinium additive enhances the open-circuit voltage and cell efficiency. This additive also retards compositional segregation into impurity phases and pinhole formation in the perovskite absorber layer during aggressive aging. Under full-spectrum simulated sunlight in ambient atmosphere, our unencapsulated and encapsulated cells retain 80 and 95% of their peak and post-burn-in efficiencies for 1010 and 1200 hours at 60° and 85°C, respectively. Our analysis reveals detailed degradation routes that contribute to the failure of aged cells.

  • Journal article
    Wang Y, Vogel A, Sachs M, Sprick RS, Wilbraham L, Moniz SJA, Godin R, Zwijnenburg MA, Durrant JR, Cooper AI, Tang Jet al., 2020,

    Current understanding and challenges of solar-driven hydrogen generation using polymeric photocatalysts (vol 4, pg 746, 2019)

    , NATURE ENERGY, Vol: 5, Pages: 633-633, ISSN: 2058-7546
  • Journal article
    Daboczi M, Kim J, Lee J, Kang H, Hamilton I, Lin C-T, Dimitrov SD, McLachlan MA, Lee K, Durrant JR, Kim J-Set al., 2020,

    Towards efficient integrated perovskite/organic bulk heterojunction solar cells: interfacial energetic requirement to reduce charge carrier recombination losses

    , Advanced Functional Materials, Vol: 30, Pages: 1-8, ISSN: 1616-301X

    Integrated perovskite/organic bulk heterojunction (BHJ) solar cells have the potential to enhance the efficiency of perovskite solar cells by a simple one‐step deposition of an organic BHJ blend photoactive layer on top of the perovskite absorber. It is found that inverted structure integrated solar cells show significantly increased short‐circuit current (J sc) gained from the complementary absorption of the organic BHJ layer compared to the reference perovskite‐only devices. However, this increase in J sc is not directly reflected as an increase in power conversion efficiency of the devices due to a loss of fill factor. Herein, the origin of this efficiency loss is investigated. It is found that a significant energetic barrier (≈250 meV) exists at the perovskite/organic BHJ interface. This interfacial barrier prevents efficient transport of photogenerated charge carriers (holes) from the BHJ layer to the perovskite layer, leading to charge accumulation at the perovskite/BHJ interface. Such accumulation is found to cause undesirable recombination of charge carriers, lowering surface photovoltage of the photoactive layers and device efficiency via fill factor loss. The results highlight a critical role of the interfacial energetics in such integrated cells and provide useful guidelines for photoactive materials (both perovskite and organic semiconductors) required for high‐performance devices.

  • Journal article
    Wang Y, Liu X, Han X, Godin R, Chen J, Zhou W, Jiang C, Thompson JF, Mustafa KB, Shevlin SA, Durrant JR, Guo Z, Tang Jet al., 2020,

    Unique hole-accepting carbon-dots promoting selective carbon dioxide reduction nearly 100% to methanol by pure water

    , NATURE COMMUNICATIONS, Vol: 11, ISSN: 2041-1723
  • Journal article
    Lin C-T, Ngiam J, Xu S, Chang Y-H, Du T, Macdonald TJ, Durrant J, McLachlan Met al., 2020,

    Enhancing the operational stability of unencapsulated perovskite solar cells through Cu-Ag bilayer electrode incorporation

    , Journal of Materials Chemistry A, Vol: 8, Pages: 8684-8691, ISSN: 2050-7488

    We identify a facile strategy that significantly reduces electrode corrosion and device degradation in unencapsulated perovskite solar cells (PSCs) operating in ambient air. By employing Cu-Ag bilayer top electrodes PSCs, we show enhanced operational lifetime compared with devices prepared from single metal (Al, Ag and Cu) analogues. Time-of-flight secondary ion mass spectrometry depth profiles indicate that the insertion of the thin layer of Cu (10nm) below the Ag (100nm) electrode significantly reduces diffusion of species originating in the perovskite active layer into the electron transport layer and electrode. X-ray diffraction (XRD) analysis reveals the mutually beneficial relationship between the bilayer metals, whereby the thermally evaporated Ag inhibits Cu oxidation and the Cu prevents interfacial reactions between the perovskite and Ag. The results here not only demonstrate a simple approach to prevent the electrode and device degradation that enhance lifetime and stability but also give an insight into ageing related ion migration and structural reorganisation.

  • Journal article
    Woods DJ, Hillman S, Pearce D, Wilbraham L, Flagg L, Duffy W, Mcculloch I, Durrant J, Guilbert A, Zwijnenburg M, Sprick RS, Nelson J, Cooper Aet al., 2020,

    Side-chain tuning in conjugated polymer photocatalysts for improved hydrogen production from water

    , Energy & Environmental Science, Vol: 13, Pages: 1843-1855, ISSN: 1754-5692

    Structure–property–activity relationships in solution processable polymer photocatalysts for hydrogen production from water were probed by varying the chemical structure of both the polymer side-chains and the polymer backbone. In both cases, the photocatalytic performance depends strongly on the inclusion of more polar groups, such as dibenzo[b,d]thiophene sulfone backbone units or oligo(ethylene glycol) side-chains. We used optical, spectroscopic, and structural characterisation techniques to understand the different catalytic activities of these systems. We find that although polar groups improve the wettability of the material with water in all cases, backbone and side-chain modifications affect photocatalytic performance in different ways: the inclusion of dibenzo[b,d]thiophene sulfone backbone units improves the thermodynamic driving force for hole transfer to the sacrificial donor, while the inclusion of oligo ethylene glycol side-chains aids the degree of polymer swelling and also extends the electron polaron lifetime. The best performing material, FS-TEG, exhibits a HER of 72.5 μmol h−1 for 25 mg photocatalyst (2.9 mmol g−1 h−1) when dispersed in the presence of a sacrificial donor and illuminated with λ > 420 nm light, corresponding to a hydrogen evolution EQE of 10% at 420 nm. When cast as a thin film, this HER was further boosted to 13.9 mmol g−1 h−1 (3.0 mmol m−2 h−1), which is among the highest rates in this field.

  • Journal article
    Kosco J, Bidwell M, Cha H, Martin T, Howells CT, Sachs M, Anjum DH, Gonzalez Lopez S, Zou L, Wadsworth A, Zhang W, Zhang L, Tellam J, Sougrat R, Laquai F, DeLongchamp DM, Durrant JR, McCulloch Iet al., 2020,

    Enhanced photocatalytic hydrogen evolution from organic semiconductor heterojunction nanoparticles

    , Nature Materials, Vol: 19, Pages: 559-565, ISSN: 1476-1122

    Photocatalysts formed from a single organic semiconductor typically suffer from inefficient intrinsic charge generation, which leads to low photocatalytic activities. We demonstrate that incorporating a heterojunction between a donor polymer (PTB7-Th) and non-fullerene acceptor (EH-IDTBR) in organic nanoparticles (NPs) can result in hydrogen evolution photocatalysts with greatly enhanced photocatalytic activity. Control of the nanomorphology of these NPs was achieved by varying the stabilizing surfactant employed during NP fabrication, converting it from a core–shell structure to an intermixed donor/acceptor blend and increasing H2 evolution by an order of magnitude. The resulting photocatalysts display an unprecedentedly high H2 evolution rate of over 60,000 µmol h−1 g−1 under 350 to 800 nm illumination, and external quantum efficiencies over 6% in the region of maximum solar photon flux.

  • Journal article
    Lee J, Lee J-H, Yao H, Cha H, Hong S, Lee S, Kim J, Durrant JR, Hou J, Lee Ket al., 2020,

    Efficient and photostable ternary organic solar cells with a narrow band gap non-fullerene acceptor and fullerene additive

    , JOURNAL OF MATERIALS CHEMISTRY A, Vol: 8, Pages: 6682-6691, ISSN: 2050-7488
  • Journal article
    Back H, Kim G, Kim H, Nam C-Y, Kim J, Kim YR, Kim T, Park B, Durrant JR, Lee Ket al., 2020,

    Highly stable inverted methylammonium lead tri-iodide perovskite solar cells achieved by surface re-crystallization

    , ENERGY & ENVIRONMENTAL SCIENCE, Vol: 13, Pages: 840-847, ISSN: 1754-5692
  • Journal article
    Spitler MT, Modestino MA, Deutsch TG, Xiang CX, Durrant JR, Esposito DV, Haussener S, Maldonado S, Sharp ID, Parkinson BA, Ginley DS, Houle FA, Hannappel T, Neale NR, Nocera DG, McIntyre PCet al., 2020,

    Practical challenges in the development of photoelectrochemical solar fuels production

    , SUSTAINABLE ENERGY & FUELS, Vol: 4, Pages: 985-995, ISSN: 2398-4902
  • Journal article
    Corby S, Francàs L, Kafizas A, Durrant JRet al., 2020,

    Determining the role of oxygen vacancies in the photoelectrocatalytic performance of WO3 for water oxidation

    , Chemical Science, Vol: 11, Pages: 2907-2914, ISSN: 2041-6520

    Oxygen vacancies are common to most metal oxides, whether intentionally incorporated or otherwise, and the study of these defects is of increasing interest for solar water splitting. In this work, we examine nanostructured WO3 photoanodes of varying oxygen content to determine how the concentration of bulk oxygen-vacancy states affects the photocatalytic performance for water oxidation. Using transient optical spectroscopy, we follow the charge carrier recombination kinetics in these samples, from picoseconds to seconds, and examine how differing oxygen vacancy concentrations impact upon these kinetics. We find that samples with an intermediate concentration of vacancies (∼2% of oxygen atoms) afford the greatest photoinduced charge carrier densities, and the slowest recombination kinetics across all timescales studied. This increased yield of photogenerated charges correlates with improved photocurrent densities under simulated sunlight, with both greater and lesser oxygen vacancy concentrations resulting in enhanced recombination losses and poorer J–V performances. Our conclusion, that an optimal – neither too high nor too low – concentration of oxygen vacancies is required for optimum photoelectrochemical performance, is discussed in terms of the competing beneficial and detrimental impact these defects have on charge separation and transport, as well as the implications held for other highly doped materials for photoelectrochemical water oxidation.

  • Journal article
    Lin C-T, Lee J, Kim J, Macdonald TJ, Ngiam J, Xu B, Daboczi M, Xu W, Pont S, Park B, Kang H, Kim J-S, Payne DJ, Lee K, Durrant JR, McLachlan MAet al., 2020,

    Origin of open-circuit voltage enhancements in planar Perovskite solar cells induced by addition of bulky organic cations

    , Advanced Functional Materials, Vol: 30, ISSN: 1616-301X

    The origin of performance enhancements in p‐i‐n perovskite solar cells (PSCs) when incorporating low concentrations of the bulky cation 1‐naphthylmethylamine (NMA) are discussed. A 0.25 vol % addition of NMA increases the open circuit voltage (Voc) of methylammonium lead iodide (MAPbI3) PSCs from 1.06 to 1.16 V and their power conversion efficiency (PCE) from 18.7% to 20.1%. X‐ray photoelectron spectroscopy and low energy ion scattering data show NMA is located at grain surfaces, not the bulk. Scanning electron microscopy shows combining NMA addition with solvent assisted annealing creates large grains that span the active layer. Steady state and transient photoluminescence data show NMA suppresses non‐radiative recombination resulting from charge trapping, consistent with passivation of grain surfaces. Increasing the NMA concentration reduces device short‐circuit current density and PCE, also suppressing photoluminescence quenching at charge transport layers. Both Voc and PCE enhancements are observed when bulky cations (phenyl(ethyl/methyl)ammonium) are incorporated, but not smaller cations (Cs/MA)—indicating size is a key parameter. Finally, it demonstrates that NMA also enhances mixed iodide/bromide wide bandgap PSCs (Voc of 1.22 V with a 1.68 eV bandgap). The results demonstrate a facile approach to maximizing Voc and provide insights into morphological control and charge carrier dynamics induced by bulky cations in PSCs.

  • Journal article
    Hamid Z, Wadsworth A, Rezasoltani E, Holliday S, Azzouzi M, Neophytou M, Guilbert AAY, Dong Y, Little MS, Mukherjee S, Herzing AA, Bristow H, Kline RJ, DeLongchamp DM, Bakulin AA, Durrant JR, Nelson J, McCulloch Iet al., 2020,

    Influence of Polymer Aggregation and Liquid Immiscibility on Morphology Tuning by Varying Composition in PffBT4T-2DT/Nonfullerene Organic Solar Cells

    , ADVANCED ENERGY MATERIALS, Vol: 10, ISSN: 1614-6832
  • Journal article
    Francas L, Corby S, Selim S, Lee D, Mesa CA, Godin R, Pastor E, Stephens IEL, Choi K-S, Durrant JRet al., 2020,

    Spectroelectrochemical study of water oxidation on nickel and iron oxyhydroxide electrocatalysts (vol 10, 5208, 2019)

    , NATURE COMMUNICATIONS, Vol: 11, ISSN: 2041-1723
  • Journal article
    Hong DP, Jain SM, Li M, Wang Z-K, Manzhos S, Feron K, Pitchaimuthu S, Liu Z, Motta N, Durrant JR, Sonar Pet al., 2020,

    All-Rounder Low-Cost Dopant-Free D-A-D Hole-Transporting Materials for Efficient Indoor and Outdoor Performance of Perovskite Solar Cells

  • Journal article
    Mesa Zamora C, Francas Forcada L, Yang KR, Garrido-Barros P, Pastor Hernandez E, Ma Y, Kafizas A, Rosser TE, Mayer MT, Reisner E, Grätzel M, Batista VS, Durrant Jet al., 2020,

    Multihole water oxidation catalysis on hematite photoanodes revealed by operando spectroelectrochemistry and DFT

    , Nature Chemistry, Vol: 12, Pages: 82-89, ISSN: 1755-4330

    Water oxidation is the key kinetic bottle neck of photoelectrochemical devices for fuel synthesis. Despite advances in the identification of intermediates, elucidating the catalytic mechanism of this multi-redox reactionon metal-oxidephotoanodes remains a significant experimental and theoretical challenge. Here we report an experimental analysis of water oxidation kinetics on four widely studied metal oxides, focusing particularly upon hematite.We observe that hematite is able toaccess a reaction mechanism third order in surface hole density, assigned to equilibration between three surface holes and M(OH)-O-M(OH) sites. This reaction exhibits a remarkably low activation energy (Ea~ 60 meV). Density functional theory is employedto determine the energetics of charge accumulation and O-O bond formation on a modelhematite 110 surface. The proposed mechanism shows parallels with the function of oxygen evolving complex of photosystem II,and provides new insights to the mechanism of heterogeneous water oxidation on a metal oxide surface.

  • Journal article
    Daboczi M, Hamilton I, Xu S, Luke J, Limbu S, Lee J, McLachlan MA, Lee K, Durrant JR, Baikie ID, Kim J-Set al., 2019,

    Origin of Open-Circuit Voltage Losses in Perovskite Solar Cells Investigated by Surface Photovoltage Measurement

    , ACS Applied Materials & Interfaces, Vol: 11, Pages: 46808-46817, ISSN: 1944-8244
  • Journal article
    Selim S, Pastor E, García-Tecedor M, Morris MR, Francas L, Sachs M, Moss B, Corby S, Mesa CA, Gimenez S, Kafizas A, Bakulin AA, Durrant JRet al., 2019,

    Impact of oxygen vacancy occupancy on charge carrier dynamics in BiVO4 photoanodes

    , Journal of the American Chemical Society, Vol: 141, Pages: 18791-18798, ISSN: 0002-7863

    Oxygen vacancies are ubiquitous in metal oxides and critical to performance, yet the impact of these states upon charge carrier dynamics important for photoelectrochemical and photocatalytic applications, remains contentious and poorly understood. A key challenge is the unambiguous identification of spectroscopic fingerprints which can be used to track their function. Herein, we employ five complementary techniques to modulate the electronic occupancy of states associated with oxygen vacancies in situ in BiVO4 photoanodes, allowing us to identify a spectral signature for the ionisation of these states. We obtain an activation energy of ̴ 0.2 eV for this ionisation process, with thermally activated electron de-trapping from these states determining the kinetics of electron extraction, consistent with improved photoelectrochemical performance at higher temperatures. Bulk, un-ionised states however, function as deep hole traps, with such trapped holes being energetically unable to drive water oxidation. These observations help address recent controversies in the literature over oxygen vacancy function, providing new insights into their impact upon photoelectrochemical performance.

  • Journal article
    Ambroz F, Xu W, Gadipelli S, Brett DJL, Lin C-T, Contini C, McLachlan MA, Durrant JR, Parkin IP, Macdonald TJet al., 2019,

    Room Temperature Synthesis of Phosphine-Capped Lead Bromide Perovskite Nanocrystals without Coordinating Solvents

  • Journal article
    Francàs L, Corby S, Selim S, Lee D, Mesa C, Godin R, Pastor E, Stephens I, Choi K-S, Durrant Jet al., 2019,

    Spectroelectrochemical study of water oxidation on nickel and iron oxyhydroxide electrocatalysts

    , Nature Communications, Vol: 10, ISSN: 2041-1723

    Ni/Fe oxyhydroxides are the best performing Earth-abundant electrocatalysts for water oxidation. However, the origin of their remarkable performance is not well understood. Herein, we employ spectroelectrochemical techniques to analyse the kinetics of water oxidation on a series of Ni/Fe oxyhydroxide films: FeOOH, FeOOHNiOOH, and Ni(Fe)OOH (5% Fe). The concentrations and reaction rates of the oxidised states accumulated during catalysis are determined. Ni(Fe)OOH is found to exhibit the fastest reaction kinetics but accumulates fewer states, resulting in a similar performance to FeOOHNiOOH. The later catalytic onset in FeOOH is attributed to an anodic shift in the accumulation of oxidised states. Rate law analyses reveal that the rate limiting step for each catalyst involves the accumulation of four oxidised states, Ni-centred for Ni(Fe)OOH but Fe-centred for FeOOH and FeOOHNiOOH. We conclude by highlighting the importance of equilibria between these accumulated species and reactive intermediates in determining the activity of these materials.

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