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Journal articleJeong S, Rana A, Kim J-H, et al., 2023,
New ternary blend strategy based on a vertically self-assembled passivation layer enabling efficient and photostable inverted organic solar cells
, Advanced Science, Vol: 10, Pages: 1-9, ISSN: 2198-3844Herein, a new ternary strategy to fabricate efficient and photostable inverted organic photovoltaics (OPVs) is introduced by combining a bulk heterojunction (BHJ) blend and a fullerene self-assembled monolayer (C60 -SAM). Time-of-flight secondary-ion mass spectrometry - analysis reveals that the ternary blend is vertically phase separated with the C60 -SAM at the bottom and the BHJ on top. The average power conversion efficiency - of OPVs based on the ternary system is improved from 14.9% to 15.6% by C60 -SAM addition, mostly due to increased current density (Jsc ) and fill factor -. It is found that the C60 -SAM encourages the BHJ to make more face-on molecular orientation because grazing incidence wide-angle X-ray scattering - data show an increased face-on/edge-on orientation ratio in the ternary blend. Light-intensity dependent Jsc data and charge carrier lifetime analysis indicate suppressed bimolecular recombination and a longer charge carrier lifetime in the ternary system, resulting in the enhancement of OPV performance. Moreover, it is demonstrated that device photostability in the ternary blend is enhanced due to the vertically self-assembled C60 -SAM that successfully passivates the ZnO surface and protects BHJ layer from the UV-induced photocatalytic reactions of the ZnO. These results suggest a new perspective to improve both performance and photostability of OPVs using a facial ternary method.
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Journal articleLee TH, Fu Y, Chin Y-C, et al., 2023,
Molecular orientation-dependent energetic shifts in solution-processed non-fullerene acceptors and their impact on organic photovoltaic performance
, Nature Communications, Vol: 14, Pages: 1-12, ISSN: 2041-1723The non-fullerene acceptors (NFAs) employed in state-of-art organic photovoltaics (OPVs) often exhibit strong quadrupole moments which can strongly impact on material energetics. Herein, we show that changing the orientation of Y6, a prototypical NFA, from face-on to more edge-on by using different processing solvents causes a significant energetic shift of up to 210 meV. The impact of this energetic shift on OPV performance is investigated in both bilayer and bulk-heterojunction (BHJ) devices with PM6 polymer donor. The device electronic bandgap and the rate of non-geminate recombination are found to depend on the Y6 orientation in both bilayer and BHJ devices, attributed to the quadrupole moment-induced band bending. Analogous energetic shifts are also observed in other common polymer/NFA blends, which correlates well with NFA quadrupole moments. This work demonstrates the key impact of NFA quadruple moments and molecular orientation on material energetics and thereby on the efficiency of high-performance OPVs.
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Journal articleHe Q, Basu A, Cha H, et al., 2023,
Ultra-Narrowband Near-Infrared Responsive J-Aggregates of Fused Quinoidal Tetracyanoindacenodithiophene
, ADVANCED MATERIALS, ISSN: 0935-9648 -
Journal articleMaimaris M, Pettipher AJ, Azzouzi M, et al., 2022,
Sub-10-fs observation of bound exciton formation in organic optoelectronic devices
, Nature Communications, Vol: 13, ISSN: 2041-1723Fundamental mechanisms underlying exciton formation in organic semiconductors are complex and elusive as it occurs on ultrashort sub-100-fs timescales. Some fundamental aspects of this process, such as the evolution of exciton binding energy, have not been resolved in time experimentally. Here, we apply a combination of sub-10-fs Pump-Push-Photocurrent, Pump-Push-Photoluminescence, and Pump-Probe spectroscopies to polyfluorene devices to track the ultrafast formation of excitons. While Pump-Probe is sensitive to the total concentration of excited states, Pump-Push-Photocurrent and Pump-Push-Photoluminescence are sensitive to bound states only, providing access to exciton binding dynamics. We find that excitons created by near-absorption-edge photons are intrinsically bound states, or become such within 10 fs after excitation. Meanwhile, excitons with a modest >0.3 eV excess energy can dissociate spontaneously within 50 fs before acquiring bound character. These conclusions are supported by excited-state molecular dynamics simulations and a global kinetic model which quantitatively reproduce experimental data.
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Journal articleXu W, Du T, Sachs M, et al., 2022,
Asymmetric charge carrier transfer and transport in planar lead halide perovskite solar cells
, Cell Reports Physical Science, Vol: 3, Pages: 1-17, ISSN: 2666-3864Understanding charge carrier extraction from the perovskite photoactive layer is critical to optimizing the design of perovskite solar cells. Herein, we demonstrate a simple time-resolved photoluminescence method to characterize the kinetics of charge transport across the bulk perovskite and charge transfer from the perovskite layer to the interlayers, elucidating the dependence of these dynamics on film thickness, grain boundaries (GBs), and interlayers. Using asymmetric laser excitation, we selectively probe charge transport by generating charges both close to and far from the heterojunction interface and correlate these results with device performance. We observe that both film thickness and GBs affect the asymmetry between electron and hole charge transport across the bulk perovskite and charge transfer from the bulk perovskite to the respective interlayers.
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Journal articlePastor E, Sachs M, Selim S, et al., 2022,
Electronic defects in metal oxide photocatalysts
, NATURE REVIEWS MATERIALS, Vol: 7, Pages: 503-521, ISSN: 2058-8437- Author Web Link
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- Citations: 17
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Journal articleRao RR, Corby S, Bucci A, et al., 2022,
Spectroelectrochemical analysis of the water oxidation mechanism on doped nickel oxides
, Journal of the American Chemical Society, Vol: 144, Pages: 7622-7633, ISSN: 0002-7863Metal oxides and oxyhydroxides exhibit state-of-the-art activity for the oxygen evolution reaction (OER); however, their reaction mechanism, particularly the relationship between charging of the oxide and OER kinetics, remains elusive. Here, we investigate a series of Mn-, Co-, Fe-, and Zn-doped nickel oxides using operando UV–vis spectroscopy coupled with time-resolved stepped potential spectroelectrochemistry. The Ni2+/Ni3+ redox peak potential is found to shift anodically from Mn- < Co- < Fe- < Zn-doped samples, suggesting a decrease in oxygen binding energetics from Mn- to Zn-doped samples. At OER-relevant potentials, using optical absorption spectroscopy, we quantitatively detect the subsequent oxidation of these redox centers. The OER kinetics was found to have a second-order dependence on the density of these oxidized species, suggesting a chemical rate-determining step involving coupling of two oxo species. The intrinsic turnover frequency per oxidized species exhibits a volcano trend with the binding energy of oxygen on the Ni site, having a maximum activity of ∼0.05 s–1 at 300 mV overpotential for the Fe-doped sample. Consequently, we propose that for Ni centers that bind oxygen too strongly (Mn- and Co-doped oxides), OER kinetics is limited by O–O coupling and oxygen desorption, while for Ni centers that bind oxygen too weakly (Zn-doped oxides), OER kinetics is limited by the formation of oxo groups. This study not only experimentally demonstrates the relation between electroadsorption free energy and intrinsic kinetics for OER on this class of materials but also highlights the critical role of oxidized species in facilitating OER kinetics.
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Journal articleKosco J, Gonzalez Carrero S, Howells CT, et al., 2022,
Generation of long-lived charges in organic semiconductor heterojunction nanoparticles for efficient photocatalytic hydrogen evolution
, Nature Energy, Vol: 7, Pages: 340-351, ISSN: 2058-7546Organic semiconductor photocatalysts for the production of solar fuels are attractive as they can be synthetically tuned to absorb visible light while simultaneously retaining suitable energy levels to drive a range of processes. However, a greater understanding of the photophysics that determines the function of organic semiconductor heterojunction nanoparticles is needed to optimize performance. Here, we show that such materials can intrinsically generate remarkably long-lived reactive charges, enabling them to efficiently drive sacrificial hydrogen evolution. Our optimized hetereojunction photocatalysts comprise the conjugated polymer PM6 matched with Y6 or PCBM electron acceptors, and achieve external quantum efficiencies of 1.0% to 5.0% at 400 to 900 nm and 8.7% to 2.6% at 400 to 700 nm, respectively. Employing transient and operando spectroscopies, we find that the heterojunction structure in these nanoparticles greatly enhances the generation of long-lived charges (millisecond to second timescale) even in the absence of electron/hole scavengers or Pt. Such long-lived reactive charges open potential applications in water-splitting Z-schemes and in driving kinetically slow and technologically desirable oxidations.
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Journal articleDu T, Macdonald TJ, Yang RX, et al., 2022,
Additive-free, low-temperature crystallization of stable alpha-FAPbI(3) perovskite
, Advanced Materials, Vol: 34, Pages: 1-10, ISSN: 0935-9648Formamidinium lead triiodide (FAPbI3) is attractive for photovoltaic devices due to its optimal bandgap at around 1.45 eV and improved thermal stability compared with methylammonium-based perovskites. Crystallization of phase-pure α-FAPbI3 conventionally requires high-temperature thermal annealing at 150 °C whilst the obtained α-FAPbI3 is metastable at room temperature. Here, aerosol-assisted crystallization (AAC) is reported, which converts yellow δ-FAPbI3 into black α-FAPbI3 at only 100 °C using precursor solutions containing only lead iodide and formamidinium iodide with no chemical additives. The obtained α-FAPbI3 exhibits remarkably enhanced stability compared to the 150 °C annealed counterparts, in combination with improvements in film crystallinity and photoluminescence yield. Using X-ray diffraction, X-ray scattering, and density functional theory simulation, it is identified that relaxation of residual tensile strains, achieved through the lower annealing temperature and post-crystallization crystal growth during AAC, is the key factor that facilitates the formation of phase-stable α-FAPbI3. This overcomes the strain-induced lattice expansion that is known to cause the metastability of α-FAPbI3. Accordingly, pure FAPbI3 p–i–n solar cells are reported, facilitated by the low-temperature (≤100 °C) AAC processing, which demonstrates increases of both power conversion efficiency and operational stability compared to devices fabricated using 150 °C annealed films.
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Journal articleLee TH, Rao RR, Pacalaj RA, et al., 2022,
A Dual Functional Polymer Interlayer Enables Near-Infrared Absorbing Organic Photoanodes for Solar Water Oxidation
, ADVANCED ENERGY MATERIALS, Vol: 12, ISSN: 1614-6832- Author Web Link
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- Citations: 4
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Journal articleDu T, Richheimer F, Frohna K, et al., 2022,
Overcoming nanoscale inhomogeneities in thin-film perovskites via exceptional post-annealing grain growth for enhanced photodetection
, Nano Letters: a journal dedicated to nanoscience and nanotechnology, Vol: 22, Pages: 979-988, ISSN: 1530-6984Antisolvent-assisted spin coating has been widely used for fabricating metal halide perovskite films with smooth and compact morphology. However, localized nanoscale inhomogeneities exist in these films owing to rapid crystallization, undermining their overall optoelectronic performance. Here, we show that by relaxing the requirement for film smoothness, outstanding film quality can be obtained simply through a post-annealing grain growth process without passivation agents. The morphological changes, driven by a vaporized methylammonium chloride (MACl)–dimethylformamide (DMF) solution, lead to comprehensive defect elimination. Our nanoscale characterization visualizes the local defective clusters in the as-deposited film and their elimination following treatment, which couples with the observation of emissive grain boundaries and excellent inter- and intragrain optoelectronic uniformity in the polycrystalline film. Overcoming these performance-limiting inhomogeneities results in the enhancement of the photoresponse to low-light (<0.1 mW cm–2) illumination by up to 40-fold, yielding high-performance photodiodes with superior low-light detection.
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Conference paperMaimaris M, Pettipher AJ, Azzouzi M, et al., 2022,
Sub-10fs Photocurrent and Photoluminescence Action Spectroscopies of Organic Optoelectronic Devices Reveals Ultrafast Formation of Bound Excitonic States
We apply ultrafast pump-push-photocurrent and pump-push-photoluminescence spectroscopies to polyfluorene organic diode to track in time the bound exciton formation. ‘Cold’-excitons become bound within 10-fs while ‘hot’-excitons can dissociate spontaneously within 50-fs before acquiring bound character.
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Journal articleMacdonald T, Clancy A, Xu W, et al., 2021,
Phosphorene nanoribbon-augmented optoelectronics for enhanced hole extraction
, Journal of the American Chemical Society, Vol: 143, Pages: 21549-21559, ISSN: 0002-7863Phosphorene nanoribbons (PNRs) have been widely predicted to exhibit a range of superlative functional properties, however since they have only recently been isolated, these properties are yet to be shown to translate to improved performance in any application. PNRs show particular promise for optoelectronics, given their predicted high exciton binding energies, tunable band gaps, and ultrahigh hole mobilities. Here, we verify the theorized enhanced hole mobility in both solar cells and space-charge-limited-current devices, demonstrating the potential for PNRs improving hole extraction in universal optoelectronic applications. Specifically, PNRs are demonstrated to act as an effective charge-selective interlayer by enhancing hole extraction from polycrystalline methylammonium lead iodide (MAPbI3) perovskite to the poly(triarylamine) semiconductor. Introducing PNRs at the hole-transport/ MAPbI3 interface achieves fill factors above 0.83 and efficiencies exceeding 21% for planar p-i-n (inverted) perovskite solar cells (PSCs). Such efficiencies are typically only reported in single-crystalline MAPbI3-based inverted PSCs. Methylammonium-free PSCs also benefit from a PNR interlayer, verifying applicability to architectures incorporating mixed perovskite absorber layers. Device photoluminescence and transient absorption spectroscopy are used to demonstrate that the presence of the PNRs drives more effective carrier extraction. Isolation of the PNRs in space-charge-limited-current hole-only devices improves both hole mobility and conductivity; demonstrating applicability beyond PSCs. This work provides primary experimental evidence that the predicted superlative functional properties of PNRs indeed translate to improved optoelectronic performance.
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Journal articleLi Y, Xu W, Mussakhanuly N, et al., 2021,
Homologous Bromides Treatment for Improving the Open-Circuit Voltage of Perovskite Solar Cells
, ADVANCED MATERIALS, Vol: 34, ISSN: 0935-9648- Author Web Link
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- Citations: 9
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Journal articleCorby S, Rao R, Steier L, et al., 2021,
The kinetics of metal oxide photoanodesfrom charge generation to catalysis
, Nature Reviews Materials, Vol: 6, Pages: 1136-1155, ISSN: 2058-8437Generating 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.
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Journal articleBozal-Ginesta C, Rao RR, Mesa CA, et al., 2021,
Redox-state kinetics in water-oxidation IrOx electrocatalysts measured by operando spectroelectrochemistry
, ACS Catalysis, Vol: 11, Pages: 15013-15025, ISSN: 2155-5435Hydrous iridium oxides (IrOx) are the best oxygen evolution electrocatalysts available for operation in acidic environments. In this study, we employ time-resolved operando spectroelectrochemistry to investigate the redox-state kinetics of IrOx electrocatalyst films for both water and hydrogen peroxide oxidation. Three different redox species involving Ir3+, Ir3.x+, Ir4+, and Ir4.y+ are identified spectroscopically, and their concentrations are quantified as a function of applied potential. The generation of Ir4.y+ states is found to be the potential-determining step for catalytic water oxidation, while H2O2 oxidation is observed to be driven by the generation of Ir4+ states. The reaction kinetics for water oxidation, determined from the optical signal decays at open circuit, accelerates from ∼20 to <0.5 s with increasing applied potential above 1.3 V versus reversible hydrogen electrode [i.e., turnover frequencies (TOFs) per active Ir state increasing from 0.05 to 2 s–1]. In contrast, the reaction kinetics for H2O2 is found to be almost independent of the applied potential (increasing from 0.1 to 0.3 s–1 over a wider potential window), indicative of a first-order reaction mechanism. These spectroelectrochemical data quantify the increase of both the density of active Ir4.y+ states and the TOFs of these states with applied positive potential, resulting in the observed sharp turn on of catalytic water oxidation current. We reconcile these data with the broader literature while providing a unique kinetic insight into IrOx electrocatalytic reaction mechanisms, indicating a first-order reaction mechanism for H2O2 oxidation driven by Ir4+ states and a higher-order reaction mechanism involving the cooperative interaction of multiple Ir4.y+ states for water oxidation.
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Journal articleGodin R, Durrant J, 2021,
Dynamics of photoconversion processes: The energetic cost of lifetime gain in photosynthetic and photovoltaic systems
, Chemical Society Reviews, Vol: 50, Pages: 13372-13409, ISSN: 0306-0012The continued development of solar energy conversion technologies relies on improved understanding of their limitations. In this review, we focus on a comparison of charge carrier dynamics underlying the function of photovoltaic devices with those of both natural and artificial photosynthetic systems. The efficiency of solar energy conversion is the product of the rate of generation of high energy species (charges for solar cells, chemical fuels for photosynthesis) and the energy contained in these species. It is known that the underlying kinetics of the photophysical and charge transfer processes affects the yield of high energy species. Comparatively little attention has been paid to how these kinetics are linked to the energy contained in the high energy species or the energy lost in driving the forward reactions. Here we review the operational parameters of both photovoltaic and photosynthetic systems to highlight the energy cost of extending the lifetime of charge carriers to levels that enable function. We show a strong correlation between the energy lost within the device and the necessary lifetime gain, even when considering natural photosynthesis alongside artificial systems. From consideration of experimental data across all these systems, the emprical energetic cost of each 10 fold increase in lifetime gain is 87 meV. This energetic cost of lifetime gain is approx. 50% greater than the 59 meV predicted from a simple kinetic model. Broadly speaking, photovoltaic devices show smaller energy losses compared to photosynthetic devices due to smaller necessary lifetime gains needed. This is because of faster charge extraction processes in photovoltaic devices compared to the complex multi-electron, multi-proton reactions to produce fuels by photosynthetic devices. The result is that in photosynthetic systems, larger energetic costs are paid to overcome unfavorable kinetic competition between the excited state lifetime and the rate of interfacial reactions. We a
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Journal articleKosco J, Gonzalez-Carrero S, Howells CT, et al., 2021,
Oligoethylene glycol side chains increase charge generation in organic semiconductor nanoparticles for enhanced photocatalytic hydrogen evolution
, Advanced Materials, Vol: 34, Pages: 1-9, ISSN: 0935-9648Organic semiconductor nanoparticles (NPs) composed of an electron donor/acceptor (D/A) semiconductor blend have recently emerged as an efficient class of hydrogen-evolution photocatalysts. It is demonstrated that using conjugated polymers functionalized with (oligo)ethylene glycol side chains in NP photocatalysts can greatly enhance their H2-evolution efficiency compared to their nonglycolated analogues. The strategy is broadly applicable to a range of structurally diverse conjugated polymers. Transient spectroscopic studies show that glycolation facilitates charge generation even in the absence of a D/A heterojunction, and further suppresses both geminate and nongeminate charge recombination in D/A NPs. This results in a high yield of photogenerated charges with lifetimes long enough to efficiently drive ascorbic acid oxidation, which is correlated with greatly enhanced H2-evolution rates in the glycolated NPs. Glycolation increases the relative permittivity of the semiconductors and facilitates water uptake. Together, these effects may increase the high-frequency relative permittivity inside the NPs sufficiently, to cause the observed suppression of exciton and charge recombination responsible for the high photocatalytic activities of the glycolated NPs.
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Journal articleLing X, Zhu H, Xu W, et al., 2021,
Combined Precursor Engineering and Grain Anchoring Leading to MA-Free, Phase-Pure, and Stable alpha-Formamidinium Lead Iodide Perovskites for Efficient Solar Cells
, ANGEWANDTE CHEMIE-INTERNATIONAL EDITION, Vol: 60, Pages: 27299-27306, ISSN: 1433-7851- Author Web Link
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- Citations: 13
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Journal articleWu J, Cha H, Du T, et al., 2021,
A Comparison of Charge Carrier Dynamics in Organic and Perovskite Solar Cells
, ADVANCED MATERIALS, Vol: 34, ISSN: 0935-9648- Author Web Link
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- Citations: 36
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Journal articleLin C-T, Xu W, Macdonald T, et al., 2021,
Correlating active layer structure and composition with device performance and lifetime in amino acid modified perovskite solar cells
, ACS Applied Materials and Interfaces, Vol: 13, Pages: 43505-43515, ISSN: 1944-8244Additive engineering is emerging as a powerful strategy to further enhance the performance of perovskite solarcells (PSCs), with the incorporation of bulky cations and amino acid (AA) derivatives being shown as a promisingstrategy for enhanced device stability. However, the incorporation of such additives typically results inphotocurrent losses owing to their saturated carbon backbones hindering charge transport and collection. Herewe investigate the use of amino acids with varying carbon chain lengths as zwitterionic additives that enhancePSC device stability, in air and nitrogen, under illumination. We discover thatstability is insensitive to chain lengthhowever, as anticipated photocurrent drops as chain length increases. Using glycine as an additive results in animprovement in open circuit voltage from 1.10 to 1.14 V and a resulting power conversion efficiency of 20.2%(20.1% stabilized). Using time-of-flight secondary ion mass spectrometry we confirm that the AAs reside at thesurfaces and interfaces of our perovskite films and propose the mechanisms by which stability is enhanced. Wehighlight this with glycine as an additive, whereby an 8-fold increase in device lifetime in ambient air at 1-sunillumination is recorded. Short circuit photoluminescence quenching of complete devices are reported and revealthat the loss in photocurrent density observed with longer carbon chain AAs results from inefficient chargeextraction from the perovskite absorber layer. These combined results demonstrate new fundamentalunderstandings in the photophysical processes of additive engineering using amino acids and provide asignificant step forward in improving the stability of high-performance PSCs.
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Journal articleWang Y, Godin R, Durrant JR, et al., 2021,
Efficient Hole Trapping in Carbon Dot/Oxygen‐Modified Carbon Nitride Heterojunction Photocatalysts for Enhanced Methanol Production from CO<sub>2</sub> under Neutral Conditions
, Angewandte Chemie, Vol: 133, Pages: 20979-20984, ISSN: 0044-8249<jats:title>Abstract</jats:title><jats:p>Artificial photosynthesis of alcohols from CO<jats:sub>2</jats:sub> is still unsatisfactory owing to the rapid charge relaxation compared to the sluggish photoreactions and the oxidation of alcohol products. Here, we demonstrate that CO<jats:sub>2</jats:sub> is reduced to methanol with 100 % selectivity using water as the only electron donor on a carbon nitride‐like polymer (FAT) decorated with carbon dots. The quantum efficiency of 5.9 % (<jats:italic>λ</jats:italic>=420 nm) is 300 % higher than the previously reported carbon nitride junction. Using transient absorption spectroscopy, we observed that holes in FAT could be extracted by the carbon dots with nearly 75 % efficiency before they become unreactive by trapping. Extraction of holes resulted in a greater density of photoelectrons, indicative of reduced recombination of shorter‐lived reactive electrons. This work offers a strategy to promote photocatalysis by increasing the amount of reactive photogenerated charges via structure engineering and extraction before energy losses by deep trapping.</jats:p>
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Journal articleDu T, Ratnasingham SR, Kosasih FU, et al., 2021,
Aerosol assisted solvent treatment: a universal method for performance and stability enhancements in perovskite solar cells
, Advanced Energy Materials, Vol: 11, ISSN: 1614-6832Metal-halide perovskite solar cells (PSCs) have had a transformative impact on the renewable energy landscape since they were first demonstrated just over a decade ago. Outstanding improvements in performance have been demonstrated through structural, compositional, and morphological control of devices, with commercialization now being a reality. Here the authors present an aerosol assisted solvent treatment as a universal method to obtain performance and stability enhancements in PSCs, demonstrating their methodology as a convenient, scalable, and reproducible post-deposition treatment for PSCs. Their results identify improvements in crystallinity and grain size, accompanied by a narrowing in grain size distribution as the underlying physical changes that drive reductions of electronic and ionic defects. These changes lead to prolonged charge-carrier lifetimes and ultimately increased device efficiencies. The versatility of the process is demonstrated for PSCs with thick (>1 µm) active layers, large-areas (>1 cm2) and a variety of device architectures and active layer compositions. This simple post-deposition process is widely transferable across the field of perovskites, thereby improving the future design principles of these materials to develop large-area, stable, and efficient PSCs.
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Journal articleWang Y, Godin R, Durrant JR, et al., 2021,
Efficient Hole Trapping in Carbon Dot/Oxygen-Modified Carbon Nitride Heterojunction Photocatalysts for Enhanced Methanol Production from CO2 under Neutral Conditions
, ANGEWANDTE CHEMIE-INTERNATIONAL EDITION, Vol: 60, Pages: 20811-20816, ISSN: 1433-7851- Author Web Link
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- Citations: 54
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Journal articleAdler C, Selim S, Krivtsov I, et al., 2021,
Photodoping and Fast Charge Extraction in Ionic Carbon Nitride Photoanodes
, ADVANCED FUNCTIONAL MATERIALS, Vol: 31, ISSN: 1616-301X- Author Web Link
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- Citations: 10
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Journal articleClarke AJ, Luke J, Meitzner R, et al., 2021,
Non-fullerene acceptor photostability and its impact on organic solar cell lifetime
, CELL REPORTS PHYSICAL SCIENCE, Vol: 2- Author Web Link
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- Citations: 18
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Journal articleMurali G, Modigunta JKR, Park S, et al., 2021,
Enhancing Light Absorption and Prolonging Charge Separation in Carbon Quantum Dots via CI-Doping for Visible-Light-Driven Photocharge-Transfer Reactions
, ACS APPLIED MATERIALS & INTERFACES, Vol: 13, Pages: 34648-34657, ISSN: 1944-8244- Author Web Link
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- Citations: 20
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Journal articleBozal-Ginesta C, Rao RR, Mesa CA, et al., 2021,
Operando spectroelectrochemistry of redox state kinetics in water-oxidation IrOx electrocatalysts
<jats:p>Hydrous iridium oxides (IrOx) are the best oxygen evolution electrocatalysts available for operation in acidic environments. In this study, we employ time-resolved operando spectroelectrochemistry to investigate the redox states kinetics of IrOx electrocatalyst films for both water and hydrogen peroxide oxidation. Three different redox species involving Ir3+, Ir4+ and Ir4.x are identified spectroscopically and their concentrations are quantified as a function of applied potential. The generation of Ir4.x+ states is found to be the potential determining step for catalytic water oxidation, whilst H2O2 oxidation is observed to be driven by the generation of Ir4+ states. The reaction kinetics for water oxidation, determined from the optical signal decays at open circuit, accelerate from ~ 20 s to < 0.5 s with increasing applied potential above 1.3V vs. RHE (i.e. TOFs per active Ir state increasing from 0.05 to 2 s-1). In contrast, the reaction kinetics for H2O2 are found to be almost independent of the applied potential (increasing from 0.1-0.3 s-1 over a wider potential window), indicative of a first order reaction mechanism. These spectroelectrochemical data quantify the increase of both the density of active Ir4.x+ states and the TOFs of these states with applied positive potential, resulting in the observed sharp turn on of catalytic water oxidation current. We reconcile these data with the broader literature while providing a new kinetic insight into IrOx electrocatalytic reaction mechanisms, indicating a first order reaction mechanism for H2O2 oxidation driven by Ir4+ states, and a higher order reaction mechanism involving the co-operative interaction of multiple Ir4.x+ states for water oxidation.</jats:p>
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Journal articleChang Y-H, Carron R, Ochoa M, et al., 2021,
Impact of RbF and NaF Postdeposition Treatments on Charge Carrier Transport and Recombination in Ga-Graded Cu(In,Ga)Se-2 Solar Cells
, ADVANCED FUNCTIONAL MATERIALS, Vol: 31, ISSN: 1616-301X- Author Web Link
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- Citations: 4
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Journal articleAdler C, Selim S, Krivtsov I, et al., 2021,
Photodoping and Fast Charge Extraction in Ionic Carbon Nitride Photoanodes
<jats:p><p>Ionic carbon nitrides based on poly(heptazineimides) (PHI) represent a vigorously studied class of materials with possibleapplications in photocatalysis and energy storage. Herein, we study, for thefirst time, the photogenerated charge dynamics in highly stable and binder-freePHI photoanodes using <i>in operando</i> transientphotocurrents and spectroelectrochemical photoinduced absorption measurements.We discover that light-induced accumulation of long-lived trapped electronswithin the PHI film leads to effective photodoping of the PHI film, resultingin a significant improvement of photocurrent response due to more efficientelectron transport. Whilephotodoping has been previously reported for various semiconductors,it has never been shown before for carbon nitride materials. Furthermore, we find that the extraction kinetics ofuntrapped electrons are remarkably fast in these PHI photoanodes, with electronextraction times (ms) comparableto those measured for commonly employed metal oxide semiconductors. These results shed lighton the excellent performance of PHI photoanodes in alcohol photoreforming,including very negative photocurrent onset, outstanding fill factor, and thepossibility to operate under zero-bias conditions. More generally, the herereported photodoping effect and fast electron extraction in PHI photoanodes establisha strong rationale for the use of PHI films in various applications, such asbias-free photoelectrochemistry or photobatteries.<br></p></jats:p>
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