588 results found
Bozal-Ginesta C, Mesa CA, Eisenschmidt A, et al., 2021, Charge accumulation kinetics in multi-redox molecular catalysts immobilised on TiO2, Chemical Science, ISSN: 2041-6520
<p>Using transient spectroelectrochemical techniques, we investigate multiply reduced states of molecular catalysts on titania photoelectrodes as a function of the applied bias and the light intensity.</p>
Nikolis VC, Dong Y, Kublitski J, et al., 2020, Field Effect versus Driving Force: Charge Generation in Small‐Molecule Organic Solar Cells, Advanced Energy Materials, Pages: 2002124-2002124, ISSN: 1614-6832
Mesa CA, Rao RR, Francàs L, et al., 2020, Reply to: Questioning the rate law in the analysis of water oxidation catalysis on haematite photoanodes., Nat Chem
Corby S, Tecedor M-G, Tengeler S, et al., 2020, Separating bulk and surface processes in NiO(x)electrocatalysts for water oxidation, SUSTAINABLE ENERGY & FUELS, Vol: 4, Pages: 5024-5030, ISSN: 2398-4902
Dong Y, Nikolis VC, Talnack F, et al., 2020, Orientation dependent molecular electrostatics drives efficient charge generation in homojunction organic sol, Nature Communications, Vol: 11, ISSN: 2041-1723
Organic solar cells usually utilise a heterojunction between electron-donating (D) and electron-accepting (A) materials to split excitons into charges. However, the use of D-A blends intrinsically limits the photovoltage and introduces morphological instability. Here, we demonstrate that polycrystalline films of chemically identical molecules offer a promising alternative and show that photoexcitation of α-sexithiophene (α-6T) films results in efficient charge generation. This leads to α-6T based homojunction organic solar cells with an external quantum efficiency reaching up to 44% and an open-circuit voltage of 1.61 V. Morphological, photoemission, and modelling studies show that boundaries between α-6T crystalline domains with different orientations generate an electrostatic landscape with an interfacial energy offset of 0.4 eV, which promotes the formation of hybridised exciton/charge-transfer states at the interface, dissociating efficiently into free charges. Our findings open new avenues for organic solar cell design where material energetics are tuned through molecular electrostatic engineering and mesoscale structural control.
Aitchison CM, Sachs M, Little MA, et al., 2020, Structure-activity relationships in well-defined conjugated oligomer photocatalysts for hydrogen production from water, CHEMICAL SCIENCE, Vol: 11, Pages: 8744-8756, ISSN: 2041-6520
Moss B, Le H, Corby S, et al., 2020, Anisotropic electron transport limits performance of Bi2WO6 photoanodes, The Journal of Physical Chemistry C, Vol: 124, Pages: 18859-18867, ISSN: 1932-7447
Bi2WO6 is one of the simplest members of the versatile Aurivillius oxide family of materials. As an intriguing model system for Aurivillius oxides, BiVO4 exhibits low water oxidation onset potentials (∼0.5–0.6 VRHE) for driven solar water oxidation. Despite this, Bi2WO6 also produces low photocurrents in comparison to other metal oxides. Due to a lack of in situ studies, the reasons for such poor performance are not understood. In this study, Bi2WO6 photoanodes are synthesized by aerosol-assisted chemical vapor deposition. The charge carrier dynamics of Bi2WO6 are studied in situ under water oxidation conditions, and the rate of both bulk recombination and water oxidation is found to be comparable to other metal oxide photoanodes. However, the rate of electron extraction is at least 10 times slower than the slowest kinetics previously reported in an oxide photoanode. First-principles analysis indicates that the slow electron extraction kinetics are linked to a strong anisotropy in the conduction band. Preferred or epitaxial growth along the conductive axes is a strategy to overcome slow electron transport and low photocurrent densities in layered materials such as Bi2WO6.
Mesa CA, Steier L, Moss B, et 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.
Achilleos DS, Yang W, Kasap H, et al., 2020, Solar Reforming of Biomass with Homogeneous Carbon Dots, ANGEWANDTE CHEMIE-INTERNATIONAL EDITION, ISSN: 1433-7851
Windle CD, Wieczorek A, Xiong L, et 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
Du T, Xu W, Xu S, et al., 2020, Light-intensity and thickness dependent efficiency of planar perovskite solar cells: charge recombination versus extraction, Journal of Materials Chemistry C, Vol: 8, Pages: 12648-12655, ISSN: 2050-7526
Photoactive layer thickness is a key parameter for optimization of photovoltaic power conversion efficiency (PCE), yet its impact on charge extraction and recombination hasn’t been fully understood in perovskite solar cells (PSCs). Herein we find that in planar PSCs the perovskite thickness yielding maximal PCE is strongly light-intensity dependent. Whilst under 1 sun irradiation the PCE is relatively invariant for perovskite thicknesses between 250 to 750 nm, at lower light intensities (0.1–0.5 sun) the thickest devices yield strongly enhanced PCE, but at higher light intensities (>1 sun) the thinnest devices give optimal PCE. Our results unravel that increased perovskite thickness leads to enhanced light absorption, reduced interfacial recombination at open circuit but greater bimolecular recombination losses at short circuit thus is suitable for devices working under weak illumination, typical of many real-world applications. Reducing perovskite thickness, however, shows the contrast trend and is suitable for PSCs working under concentrated illumination.
Hou B, Kim B-S, Lee HKH, et al., 2020, Multiphoton Absorption Stimulated Metal Chalcogenide Quantum Dot Solar Cells under Ambient and Concentrated Irradiance, ADVANCED FUNCTIONAL MATERIALS, Vol: 30, ISSN: 1616-301X
Sachs M, Cha H, Kosco J, et al., 2020, Tracking charge transfer to residual metal clusters in conjugated polymers for photocatalytic hydrogen evolution, Journal of the American Chemical Society, Vol: 142, Pages: 14574-14587, ISSN: 0002-7863
Semiconducting polymers are versatile materials for solar energy conversion and have gained popularity as photocatalysts for sunlight-driven hydrogen production. Organic polymers often contain residual metal impurities such as palladium (Pd) clusters that are formed during the polymerization reaction, and there is increasing evidence for a catalytic role of such metal clusters in polymer photocatalysts. Using transient and operando optical spectroscopies on nanoparticles of F8BT, P3HT, and the dibenzo[b,d]thiophene sulfone homopolymer, P10, we demonstrate how differences in the timescale of electron transfer to Pd clusters translate into hydrogen evolution activity optima at extremely different residual Pd concentrations. For F8BT nanoparticles with common Pd concentrations of >1000 ppm (>0.1 wt. %), we find that residual Pd clusters quench photogenerated excitons via energy and electron transfer on the fs – ns timescale, thus outcompeting reductive quenching. We spectroscopically identify reduced Pd clusters in our F8BT nanoparticles from the µs timescale onwards and show that the predominant location of long-lived electrons gradually shifts to the F8BT polymer when the Pd content is lowered. While a low yield of long-lived electrons limits the hydrogen evolution activity of F8BT, P10 exhibits a substantially higher hydrogen evolution activity which we demonstrate results from higher yields of long-lived electrons due to more efficient reductive quenching. Surprisingly, and despite the higher performance of P10, long-lived electrons reside on the P10 polymer rather than on the Pd clusters in P10 particles, even at very high Pd concentrations of 27,000 ppm (2.7 wt. %). In contrast, long-lived electrons in F8BT already reside on Pd clusters before the typical timescale of hydrogen evolution. This comparison shows that P10 exhibits efficient reductive quenching but slow electron transfer to residual Pd clusters whereas the opposite is the case for F8
Lee J, Cha H, Yao H, et 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
Cha H, Zheng Y, Dong Y, et 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.
Wu J, Lee J, Chin Y-C, et 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.
Lin Y-H, Sakai N, Da P, et 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.
Mohapatra AA, Dong Y, Boregowda P, et al., 2020, Rational Design of Donor Acceptor Based Semiconducting Copolymers with High Dielectric Constant
<jats:p><div> <div> <div> <p>An efficient photogeneration of free charge carriers has long been recognized as theparamount challenge in organic photovoltaic (OPV) devices. The low dielectric constantorganic semiconductors fall short to reduce strong Coulombic interaction of tightly boundexciton and hence lead to a loss mechanism in OPVs due to charge-carrier recombination. Tocircumvent this problem, we adopt a strategy to enhance the dielectric constant of organicsemiconductors by incorporating tetraethyleneglycol (TEG) side-chains. We report synthesisof three new semiconducting copolymers by combining thiophene substituteddiketopyrrolopyrrole (TDPP) monomer with three other monomeric units with varyingelectron donating strength: benzodithiophene (BBT-3TEG-TDPP), TDPP (TDPP-3TEG-TDPP)and naphthalene diimide (PNDITEG-TDPP). BBT-3TEG-TDPP and PNDITEG-TDPP showedhighest dielectric constants (~ 5) at 1MHz frequency suggesting efficient contribution ofdipolar polarization from TEG side-chains. To understand the electronic contribution of thepolymer backbone and the polarity of TEG side-chains, and the resulting enhancement of thedielectric constant, we further performed first-principles density functional theorycalculations. Single-component organic solar cells (OSC) fabricated utilizing these polymersresulted in poor performance which is attributed to the absence of free charge generation.Furthermore, transient absorption spectroscopy studies show low exciton diffusion length asobserved in donor-acceptor type conjugated polymers. Our results suggest that, the strategyof enhancing dielectric constant with polar side-chains is not sufficient to reduce Coulombicinteraction between hole and electron in OSCs.</p> </div> </div> </div></jats:p>
Mesa CA, Steier L, Moss B, et al., 2020, Impact Of Synthesis Route on the Water Oxidation Kinetics of Hematite Photoanodes, Publisher: American Chemical Society (ACS)
<jats:p><p><i>Operando</i> 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. Lower photoanode performance was found to correlate with the observation of optical signals indicative of charge accumulation in mid-gap oxygen vacancy states, indicating these states do not contribute directly to water oxidation.</p></jats:p>
Wang Y, Vogel A, Sachs M, et 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
Daboczi M, Kim J, Lee J, et 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.
Wang Y, Liu X, Han X, et 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
Lin C-T, Ngiam J, Xu S, et 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.
Woods DJ, Hillman S, Pearce D, et 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.
Durrant J, 2020, Outstanding Reviewers for Sustainable Energy & Fuels in 2019, SUSTAINABLE ENERGY & FUELS, Vol: 4, Pages: 2086-2086, ISSN: 2398-4902
Lee J, Lee J-H, Yao H, et 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
Spitler MT, Modestino MA, Deutsch TG, et al., 2020, Practical challenges in the development of photoelectrochemical solar fuels production, SUSTAINABLE ENERGY & FUELS, Vol: 4, Pages: 985-995, ISSN: 2398-4902
Back H, Kim G, Kim H, et 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
Corby S, Francàs L, Kafizas A, et 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.
Lin C-T, Lee J, Kim J, et 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.
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