659 results found
Hußner M, Pacalaj RA, Olaf Müller-Dieckert G, et al., 2024, Machine Learning for Ultra High Throughput Screening of Organic Solar Cells: Solving the Needle in the Haystack Problem, Advanced Energy Materials, Vol: 14, ISSN: 1614-6832
Over the last two decades the organic solar cell community has synthesized tens of thousands of novel polymers and small molecules in the search for an optimum light harvesting material. These materials are often crudely evaluated simply by measuring the current–voltage (JV) curves in the light to obtain power conversion efficiencies (PCEs). Materials with low PCEs are quickly disregarded in the search for higher efficiencies. More complex measurements such as frequency/time domain characterization that could explain why the material performed as it is often not performed as they are too time consuming/complex. This limited feedback forced the field to advance using a more or less random walk of material development and has significantly slowed progress. Herein, a simple technique based on machine learning that can quickly and accurately extract recombination time constants and charge carrier mobilities as a function of light intensity simply from light/dark JV curves alone. This technique reduces the time to fully analyze a working cell from weeks to seconds and opens up the possibility of not only fully characterizing new devices as they are fabricated, but also data mining historical data sets for promising materials the community has overlooked.
Park SY, Labanti C, Pacalaj RA, et al., 2023, The state-of-the-art solution-processed single component organic photodetectors achieved by strong quenching of intermolecular emissive state and high quadrupole moment in non-fullerene acceptors, Advanced Materials, Vol: 35, ISSN: 0935-9648
A bulk-heterojunction (BHJ) blend is commonly used as the photoactive layer in organic photodetectors (OPDs) to utilize the donor (D)/acceptor (A) interfacial energetic offset for exciton dissociation. However, this strategy often complicates optimization procedures, raising serious concerns over device processability, reproducibility, and stability. Herein, highly efficient OPDs fabricated with single-component organic semiconductors are demonstrated via solution-processing. The non-fullerene acceptors (NFAs) with strong intrinsic D/A character are used as the photoactive layer, where the emissive intermolecular charge transfer excitonic (CTE) states are formed within <1 ps, and efficient photocurrent generation is achieved via strong quenching of these CTE states by reverse bias. Y6 and IT-4F-based OPDs show excellent OPD performances, low dark current density (≈10-9 A cm-2 ), high responsivity (≥0.15 A W-1 ), high specific detectivity (>1012 Jones), and fast photo-response time (<10 µs), comparable to the state-of-the-art BHJ OPDs. Together with strong CTE state quenching by electric field, these excellent OPD performances are also attributed to the high quadrupole moments of NFA molecules, which can lead to large interfacial energetic offset for efficient CTE dissociation. This work opens a new way to realize efficient OPDs using single-component systems via solution-processing and provides important molecular design rules.
Wilson AA, Hart L, Shalvey T, et al., 2023, Transient absorption spectroscopy reveals that slow bimolecular recombination in SrTiO3 underpins its efficient photocatalytic performance., Chem Commun (Camb), Vol: 59, Pages: 13579-13582
The charge carrier dynamics of SrTiO3 are measured by ultrafast transient absorption spectroscopy, revealing bimolecular recombination kinetics that are at least two magnitudes slower than alternative metal oxides. This slow recombination is associated with its high dielectric constant, and suggested to be central to SrTiO3's high performance in photocatalytic systems.
Wilson AA, Shalvey TP, Kafizas A, et al., 2023, Analysis of charge trapping and long lived hole generation in SrTiO₃ photoanodes, Sustainable Energy & Fuels, Vol: 7, Pages: 5066-5075, ISSN: 2398-4902
Charge carrier dynamics studies of SrTiO3 under applied bias offer the opportunity to gain unique insights into what underpins its state-of-the-art photocatalytic water splitting activity. Herein, time resolved spectroscopic measurements are employed, to investigate the impact of applied bias on the transient and steady state charge carrier dynamics of SrTiO3 across μs–s timescales, and simultaneously measure charge extraction kinetics. A high density of Ti3+ defect states in SrTiO3 photoanodes are identified and associated with prevalent electron trapping into deep states, which is in competition with electron extraction and limits the photocurrent. Despite the high density of trapped electrons, an intrinsically long lifetime for photogenerated holes in SrTiO3 photoanodes is observed using transient absorption spectroscopy, even in the absence of applied bias. This is important for overcoming the slow kinetics and hole accumulation associated with the water oxidation reaction, and for enabling good performance in photocatalytic systems where bias cannot be applied.
Xu W, Hart LJF, Moss B, et al., 2023, Impact of Interface Energetic Alignment and Mobile Ions on Charge Carrier Accumulation and Extraction in p-i-n Perovskite Solar Cells, ADVANCED ENERGY MATERIALS, Vol: 13, ISSN: 1614-6832
Meng Z, Pastor E, Selim S, et al., 2023, Operando IR optical control of localized charge carriers in BiVO4 photoanodes, Journal of the American Chemical Society, Vol: 145, Pages: 17700-17709, ISSN: 0002-7863
In photoelectrochemical cells (PECs) the photon-to-current conversion efficiency is often governed by carrier transport. Most metal oxides used in PECs exhibit thermally activated transport due to charge localization via the formation of polarons or the interaction with defects. This impacts catalysis by restricting the charge accumulation and extraction. To overcome this transport bottleneck nanostructuring, selective doping and photothermal treatments have been employed. Here we demonstrate an alternative approach capable of directly activating localized carriers in bismuth vanadate (BiVO4). We show that IR photons can optically excite localized charges, modulate their kinetics, and enhance the PEC current. Moreover, we track carriers bound to oxygen vacancies and expose their ∼10 ns charge localization, followed by ∼60 μs transport-assisted trapping. Critically, we demonstrate that localization is strongly dependent on the electric field within the device. While optical modulation has still a limited impact on overall PEC performance, we argue it offers a path to control devices on demand and uncover defect-related photophysics.
Qian D, Pratik SM, Liu Q, et al., 2023, Correlating the Hybridization of Local-Exciton and Charge-Transfer States with Charge Generation in Organic Solar Cells, ADVANCED ENERGY MATERIALS, ISSN: 1614-6832
Panidi J, Mazzolini E, Eisner F, et al., 2023, Biorenewable solvents for high-performance organic solar cells, ACS Energy Letters, Vol: 8, Pages: 3038-3047, ISSN: 2380-8195
With the advent of nonfullerene acceptors (NFAs), organic photovoltaic (OPV) devices are now achieving high enough power conversion efficiencies (PCEs) for commercialization. However, these high performances rely on active layers processed from petroleum-based and toxic solvents, which are undesirable for mass manufacturing. Here, we demonstrate the use of biorenewable 2-methyltetrahydrofuran (2MeTHF) and cyclopentyl methyl ether (CPME) solvents to process donor: NFA-based OPVs with no additional additives in the active layer. Furthermore, to reduce the overall carbon footprint of the manufacturing cycle of the OPVs, we use polymeric donors that require a few synthetic steps for their synthesis, namely, PTQ10 and FO6-T, which are blended with the Y-series NFA Y12. High performance was achieved using 2MeTHF as the processing solvent, reaching PCEs of 14.5% and 11.4% for PTQ10:Y12 and FO6-T:Y12 blends, respectively. This work demonstrates the potential of using biorenewable solvents without additives for the processing of OPV active layers, opening the door to large-scale and green manufacturing of organic solar cells.
Jiang Z, Du T, Lin C, et al., 2023, Deciphering the role of hole transport layer HOMO level on the open circuit voltage of perovskite Solar cells, Advanced Materials Interfaces, Vol: 10, ISSN: 2196-7350
With the rapid development of perovskite solar cells, reducing losses in open-circuit voltage (Voc) is a key issue in efforts to further improve device performance. Here it is focused on investigating the correlation between the highest occupied molecular orbital (HOMO) of device hole transport layers (HTLs) and device Voc. To achieve this, structurally similar HTL materials with comparable optical band gaps and doping levels, but distinctly different HOMO levels are employed. Using light-intensity dependent Voc and photoluminescence measurements significant differences in the behavior of devices employing the two HTLs are highlighted. Light-induced increase of quasi-Fermi level splitting (ΔEF) in the perovskite layer results in interfacial quasi-Fermi level bending required to align with the HOMO level of the HTL, resulting in the Voc measured at the contacts being smaller than the ΔEF in the perovskite. It is concluded that minimizing the energetic offset between HTLs and the perovskite active layer is of great importance to reduce non-radiative recombination losses in perovskite solar cells with high Voc values that approach the radiative limit.
Lee TH, Hillman SAJ, Gonzalez-Carrero S, et al., 2023, Long-Lived Charges in Y6:PM6 Bulk-Heterojunction Photoanodes with a Polymer Overlayer Improve Photoelectrocatalytic Performance, ADVANCED ENERGY MATERIALS, Vol: 13, ISSN: 1614-6832
Jeong 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: 2198-3844
Herein, 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.
Moruzzi F, Zhang W, Purushothaman B, et al., 2023, Solution-processable polymers of intrinsic microporosity for gas-phase carbon dioxide photoreduction, NATURE COMMUNICATIONS, Vol: 14
Aitchison CM, Gonzalez-Carrero S, Yao S, et al., 2023, Templated 2D Polymer Heterojunctions for Improved Photocatalytic Hydrogen Production, ADVANCED MATERIALS, ISSN: 0935-9648
Davies KR, Allan MG, Nagarajan S, et al., 2023, Solar light-driven simultaneous pharmaceutical pollutant degradation and green hydrogen production using a mesoporous nanoscale WO<sub>3</sub>/BiVO<sub>4</sub> heterostructure photoanode, JOURNAL OF ENVIRONMENTAL CHEMICAL ENGINEERING, Vol: 11, ISSN: 2213-2929
Mohapatra AA, Pranav M, Yadav S, et al., 2023, Interface engineering in perylene diimide-based organic photovoltaics with enhanced photovoltage, ACS Applied Materials and Interfaces, Vol: 15, Pages: 25224-25231, ISSN: 1944-8244
The introduction of nonfullerene acceptors (NFA) facilitated the realization of high-efficiency organic solar cells (OSCs); however, OSCs suffer from relatively large losses in open-circuit voltage (VOC) as compared to inorganic or perovskite solar cells. Further enhancement in power conversion efficiency requires an increase in VOC. In this work, we take advantage of the high dipole moment of twisted perylene-diimide (TPDI) as a nonfullerene acceptor (NFA) to enhance the VOC of OSCs. In multiple bulk heterojunction solar cells incorporating TPDI with three polymer donors (PTB7-Th, PM6 and PBDB-T), we observed a VOC enhancement by modifying the cathode with a polyethylenimine (PEIE) interlayer. We show that the dipolar interaction between the TPDI NFA and PEIE─enhanced by the general tendency of TPDI to form J-aggregates─plays a crucial role in reducing nonradiative voltage losses under a constant radiative limit of VOC. This is aided by comparative studies with PM6:Y6 bulk heterojunction solar cells. We hypothesize that incorporating NFAs with significant dipole moments is a feasible approach to improving the VOC of OSCs.
Collado L, Gomez-Mendoza M, Garcia-Tecedor M, et al., 2023, Towards the improvement of methane production in CO2 photoreduction using Bi2WO6/TiO2 heterostructures, APPLIED CATALYSIS B-ENVIRONMENTAL, Vol: 324, ISSN: 0926-3373
Lee 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: 2041-1723
The 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.
He Q, Basu A, Cha H, et al., 2023, Ultra-Narrowband Near-Infrared Responsive J-Aggregates of Fused Quinoidal Tetracyanoindacenodithiophene, ADVANCED MATERIALS, Vol: 35, ISSN: 0935-9648
Song H, Yang J, Jeong WH, et al., 2023, A Universal Perovskite Nanocrystal Ink for High-Performance Optoelectronic Devices, ADVANCED MATERIALS, Vol: 35, ISSN: 0935-9648
Luke J, Jo Y-R, Lin C-T, et al., 2022, The molecular origin of high performance in ternary organic photovoltaics identified using a combination of in situ structural probes, Journal of Materials Chemistry A, Vol: 11, Pages: 1281-1289, ISSN: 2050-7488
A ternary blend, wherein a tertiary acceptor is incorporated into a donor:non-fullerene acceptor (NFA) binary blend has emerged as a promising strategy for improving power conversion efficiency and stability of organic bulk heterojunction photovoltaics (OPVs). However, the effects of the tertiary component remain elusive due to the complex variation of crystallinity and morphology of donor and acceptor phases during thermal annealing. Herein a combination of in situ transmission electron microscopy and X-ray diffraction spectroscopy utilized during annealing identifies that (1) the addition of the tertiary component (O-IDFBR) delays the glass transition temperature of edge-on-oriented polymer donor (P3HT), prohibits the glass transition of face-on-oriented polymer donor (P3HT), broadens the crystallization temperature of O-IDTBR, and enhances the overall crystallinity of the donor and acceptor phases (P3HT and O-IDTBR), and (2) the ternary component induces homogeneously distributed nanoscale domains rather than a microscale separation between the donor and acceptor as observed in the binary blend. The optimized nanoscale domain morphology, driven by slower crystallization and enhanced overall crystallinity leads to a more stable morphology, resulting in superior device performance and stability.
Luo H, Yukuhiro VY, Fernandez PS, et al., 2022, Role of Ni in PtNi Bimetallic Electrocatalysts for Hydrogen and Value-Added Chemicals Coproduction via Glycerol Electrooxidation, ACS CATALYSIS, Vol: 12, Pages: 14492-14506, ISSN: 2155-5435
Lee TH, Dong Y, Pacalaj RA, et al., 2022, Organic Planar Heterojunction Solar Cells and Photodetectors Tailored to the Exciton Diffusion Length Scale of a Non-Fullerene Acceptor, ADVANCED FUNCTIONAL MATERIALS, Vol: 32, ISSN: 1616-301X
Hillman SAJ, Sprick RS, Pearce D, et al., 2022, Why do sulfone-containing polymer photocatalysts work so well for sacrificial hydrogen evolution from water?, Journal of the American Chemical Society, Vol: 144, Pages: 19382-19395, ISSN: 0002-7863
Many of the highest-performing polymer photocatalysts for sacrificial hydrogen evolution from water have contained dibenzo[b,d]thiophene sulfone units in their polymer backbones. However, the reasons behind the dominance of this building block are not well understood. We study films, dispersions, and solutions of a new set of solution-processable materials, where the sulfone content is systematically controlled, to understand how the sulfone unit affects the three key processes involved in photocatalytic hydrogen generation in this system: light absorption; transfer of the photogenerated hole to the hole scavenger triethylamine (TEA); and transfer of the photogenerated electron to the palladium metal co-catalyst that remains in the polymer from synthesis. Transient absorption spectroscopy and electrochemical measurements, combined with molecular dynamics and density functional theory simulations, show that the sulfone unit has two primary effects. On the picosecond timescale, it dictates the thermodynamics of hole transfer out of the polymer. The sulfone unit attracts water molecules such that the average permittivity experienced by the solvated polymer is increased. We show that TEA oxidation is only thermodynamically favorable above a certain permittivity threshold. On the microsecond timescale, we present experimental evidence that the sulfone unit acts as the electron transfer site out of the polymer, with the kinetics of electron extraction to palladium dictated by the ratio of photogenerated electrons to the number of sulfone units. For the highest-performing, sulfone-rich material, hydrogen evolution seems to be limited by the photogeneration rate of electrons rather than their extraction from the polymer.
Pulignani C, Mesa C, Hillman S, et al., 2022, Rational design of carbon nitride photoelectrodes with high activity toward organic oxidations, Angewandte Chemie International Edition, ISSN: 1433-7851
Carbon nitride (CNx) is a scalable polymeric light-absorber with excellent performance in photocatalytic suspension systems, but the activity of CNx photoelectrodes has remained low. Here, cyanamide-functionalized CNx (NCNCNx) has been co-deposited with ITO nanoparticles on a 1.8 Å thick alumina-coated FTO-glass electrode. Transient spectroscopy and impedance measurements support that ITO acts as conductive binder and improves the electron extraction from the NCNCNx, whilst the alumina underlayer reduces the electrical resistance between the ITO and the FTO-coated electrode. The Al2O3|ITO:NCNCNx electrode displays a new benchmark performance for CNx-based photoanodes with a remarkably low onset of –0.4 V vs the reversible hydrogen electrode (RHE) and an outstanding 1.4 ± 0.2 mA cm–2 at 1.23 V vs RHE for the selective oxidation of 4-methylbenzyl alcohol to the corresponding aldehyde. This facile assembly will enable the exploration of CNx in fundamental and applied PEC studies, paving the way for the development of high-performance photoelectrodes using other semiconductor powders
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, Vol: 32, ISSN: 1616-301X
Rao RR, Mesa CA, Durrant JR, 2022, Better together, NATURE CATALYSIS, Vol: 5, Pages: 844-845, ISSN: 2520-1158
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
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