634 results found
Lin C-T, Hsieh C-T, Macdonald TJ, et al., 2022, Water-Insensitive Electron Transport and Photoactive Layers for Improved Underwater Stability of Organic Photovoltaics, ADVANCED FUNCTIONAL MATERIALS, ISSN: 1616-301X
Labanti C, Wu J, Shin J, et al., 2022, Light-intensity dependent photoresponse time of organic photodetectors and its molecular origin, Nature Communications, Vol: 13, Pages: 1-10, ISSN: 2041-1723
Organic photodetectors (OPDs) exhibit superior spectral responses but slower photoresponse times compared to inorganic counterparts. Herein, we study the light-intensity-dependent OPD photoresponse time with two small-molecule donors (planar MPTA or twisted NP-SA) co-evaporated with C 60 acceptors. MPTA:C60 exhibits the fastest response time at high-lightintensities (>0.5 mW/cm 2), attributed to its planar structure favoring strong intermolecular interactions. However, this blend exhibits the slowest response at low-light intensities, which is correlated with biphasic photocurrent transients indicative of the pr esence of a low density of deep trap states. Optical, structural and en ergetical analyses indicate that MPTA molecular packing is strongly disrupted by C 60, resulting in a larger (370 meV) HOMO level shift. This results in greater energetic inhomogeneity including possible MPTA-C 60 adduct formation, leading to deep trap states which limit the low-light photoresponse time. This work provides important insights into the small molecule design rules critical for low charge-trapping and high-speed OPD applications.
Xu 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: 2666-3864
Understanding 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.
Bozal-Ginesta C, Rao RR, Mesa CA, et al., 2022, Spectroelectrochemistry of Water Oxidation Kinetics in Molecularversus Heterogeneous Oxide Iridium Electrocatalysts, JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, Vol: 144, Pages: 8454-8459, ISSN: 0002-7863
Rao 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: 0002-7863
Kosco 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: 2058-7546
Organic 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.
Du 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: 0935-9648
Formamidinium 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.
Lee 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
Du 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: 1530-6984
Antisolvent-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.
Macdonald 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: 0002-7863
Phosphorene 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.
Li 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
Corby 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: 2058-8437
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.
Bozal-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: 2155-5435
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-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.
Kosco 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: 0935-9648
Organic 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.
Ling 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
Godin 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: 0306-0012
The 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
Wu 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
Lin 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: 1944-8244
Additive 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.
Wang 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
Du 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: 1614-6832
Metal-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.
Wang 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
Adler 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
Clarke 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
Murali 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
Chang 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
Adler C, Selim S, Krivtsov I, et al., 2021, Photodoping and Fast Charge Extraction in Ionic Carbon Nitride Photoanodes
<jats:p>Ionic carbon nitrides based on poly(heptazine imides) (PHI) represent a vigorously studied class of materials with possible applications in photocatalysis and energy storage. Herein, we study, for the first time, the photogenerated charge dynamics in highly stable and binder-free PHI photoanodes using <jats:italic>in operando</jats:italic> transient photocurrents and spectroelectrochemical photoinduced absorption measurements. We discover that light-induced accumulation of long-lived trapped electrons within the PHI film leads to effective photodoping of the PHI film, resulting in a significant improvement of photocurrent response due to more efficient electron transport. While photodoping has been previously reported for various semiconductors, it has never been shown before for carbon nitride materials. Furthermore, we find that the extraction kinetics of untrapped electrons are remarkably fast in these PHI photoanodes, with electron extraction times (ms) comparable to those measured for commonly employed metal oxide semiconductors. These results shed light on the excellent performance of PHI photoanodes in alcohol photoreforming, including very negative photocurrent onset, outstanding fill factor, and the possibility to operate under zero-bias conditions. More generally, the here reported photodoping effect and fast electron extraction in PHI photoanodes establish a strong rationale for the use of PHI films in various applications, such as bias-free photoelectrochemistry or photobatteries.</jats:p><jats:p />
Jones B, Davies KR, Allan MG, et al., 2021, Photoelectrochemical concurrent hydrogen generation and heavy metal recovery from polluted acidic mine water, SUSTAINABLE ENERGY & FUELS, Vol: 5, Pages: 3084-3091, ISSN: 2398-4902
Bucci A, Garcia-Tecedor M, Corby S, et 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
Francas L, Selim S, Corby S, et al., 2021, Water oxidation kinetics of nanoporous BiVO4 photoanodes functionalised with nickel/iron oxyhydroxide electrocatalysts, CHEMICAL SCIENCE, Vol: 12, Pages: 7442-7452, ISSN: 2041-6520
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