Publications
641 results found
Strohm S, Machui F, Langner S, et al., 2018, P3HT: non-fullerene acceptor based large area, semi-transparent PV modules with power conversion efficiencies of 5%, processed by industrially scalable methods, ENERGY & ENVIRONMENTAL SCIENCE, Vol: 11, Pages: 2225-2234, ISSN: 1754-5692
Liang R-Z, Babics M, Savikhin V, et al., 2018, Carrier Transport and Recombination in Efficient "All-Small-Molecule" Solar Cells with the Nonfullerene Acceptor IDTBR, ADVANCED ENERGY MATERIALS, Vol: 8, ISSN: 1614-6832
Gasparini N, Gregori A, Salvador M, et al., 2018, Visible and Near-Infrared Imaging with Nonfullerene-Based Photodetectors, ADVANCED MATERIALS TECHNOLOGIES, Vol: 3, ISSN: 2365-709X
Neophytou M, Bryant D, Lopatin S, et al., 2018, Alternative Thieno[3,2-b][1]benzothiophene Isoindigo Polymers for Solar Cell Applications, MACROMOLECULAR RAPID COMMUNICATIONS, Vol: 39, ISSN: 1022-1336
Pappa A-M, Ohayon D, Giovannitti A, et al., 2018, Direct metabolite detection with an n-type accumulation mode organic electrochemical transistor, Science Advances, Vol: 4, ISSN: 2375-2548
The inherent specificity and electrochemical reversibility of enzymes poise them as the biorecognition element of choice for a wide range of metabolites. To use enzymes efficiently in biosensors, the redox centers of the protein should have good electrical communication with the transducing electrode, which requires either the use of mediators or tedious biofunctionalization approaches. We report an all-polymer micrometer-scale transistor platform for the detection of lactate, a significant metabolite in cellular metabolic pathways associated with critical health care conditions. The device embodies a new concept in metabolite sensing where we take advantage of the ion-to-electron transducing qualities of an electron-transporting (n-type) organic semiconductor and the inherent amplification properties of an ion-to-electron converting device, the organic electrochemical transistor. The n-type polymer incorporates hydrophilic side chains to enhance ion transport/injection, as well as to facilitate enzyme conjugation. The material is capable of accepting electrons of the enzymatic reaction and acts as a series of redox centers capable of switching between the neutral and reduced state. The result is a fast, selective, and sensitive metabolite sensor. The advantage of this device compared to traditional amperometric sensors is the amplification of the input signal endowed by the electrochemical transistor circuit and the design simplicity obviating the need for a reference electrode. The combination of redox enzymes and electron-transporting polymers will open up an avenue not only for the field of biosensors but also for the development of enzyme-based electrocatalytic energy generation/storage devices.
Inal S, Rivnay J, Suiu A-O, et al., 2018, Conjugated Polymers in Bioelectronics, ACCOUNTS OF CHEMICAL RESEARCH, Vol: 51, Pages: 1368-1376, ISSN: 0001-4842
Li N, McCulloch I, Brabec CJ, 2018, Analyzing the efficiency, stability and cost potential for fullerene-free organic photovoltaics in one figure of merit, ENERGY & ENVIRONMENTAL SCIENCE, Vol: 11, Pages: 1355-1361, ISSN: 1754-5692
Baran D, Gasparini N, Wadsworth A, et al., 2018, Robust nonfullerene solar cells approaching unity external quantum efficiency enabled by suppression of geminate recombination, Nature Communications, Vol: 9, ISSN: 2041-1723
Nonfullerene solar cells have increased their efficiencies up to 13%, yet quantum efficiencies are still limited to 80%. Here we report efficient nonfullerene solar cells with quantum efficiencies approaching unity. This is achieved with overlapping absorption bands of donor and acceptor that increases the photon absorption strength in the range from about 570 to 700 nm, thus, almost all incident photons are absorbed in the active layer. The charges generated are found to dissociate with negligible geminate recombination losses resulting in a short-circuit current density of 20 mA cm−2 along with open-circuit voltages >1 V, which is remarkable for a 1.6 eV bandgap system. Most importantly, the unique nano-morphology of the donor:acceptor blend results in a substantially improved stability under illumination. Understanding the efficient charge separation in nonfullerene acceptors can pave the way to robust and recombination-free organic solar cells.
Zhang Y, Wustoni S, Savva A, et al., 2018, Lipid bilayer formation on organic electronic materials, JOURNAL OF MATERIALS CHEMISTRY C, Vol: 6, Pages: 5218-5227, ISSN: 2050-7526
Giovannitti A, Thorley K, Nielsen C, et al., 2018, Redox-stability of alkoxy-BDT copolymers and their use for organic bioelectronic devices, Advanced Functional Materials, Vol: 28, ISSN: 1616-301X
Organic semiconductors can be employed as the active layer in accumulation mode organic electrochemical transistors (OECTs), where redox stability in aqueous electrolytes is important for long‐term recordings of biological events. It is observed that alkoxy‐benzo[1,2‐b:4,5‐b′]dithiophene (BDT) copolymers can be extremely unstable when they are oxidized in aqueous solutions. The redox stability of these copolymers can be improved by molecular design of the copolymer where it is observed that the electron rich comonomer 3,3′‐dimethoxy‐2,2′‐bithiophene (MeOT2) lowers the oxidation potential and also stabilizes positive charges through delocalization and resonance effects. For copolymers where the comonomers do not have the same ability to stabilize positive charges, irreversible redox reactions are observed with the formation of quinone structures, being detrimental to performance of the materials in OECTs. Charge distribution along the copolymer from density functional theory calculations is seen to be an important factor in the stability of the charged copolymer. As a result of the stabilizing effect of the comonomer, a highly stable OECT performance is observed with transconductances in the mS range. The analysis of the decomposition pathway also raises questions about the general stability of the alkoxy‐BDT unit, which is heavily used in donor–acceptor copolymers in the field of photovoltaics.
Gasparini N, Wadsworth A, Moser M, et al., 2018, The Physics of Small Molecule Acceptors for Efficient and Stable Bulk Heterojunction Solar Cells, ADVANCED ENERGY MATERIALS, Vol: 8, ISSN: 1614-6832
Giovannitti A, Maria I, Hanifi D, et al., 2018, The role of the side chain on the performance of n-type conjugated polymers in aqueous electrolytes, Chemistry of Materials, Vol: 30, Pages: 2945-2953, ISSN: 0897-4756
We report a design strategy that allows the preparation of solution processable n type materials from low boiling point solvents for organic electrochemical transistors (OECTs). The polymer backbone is based on NDI-T2 copolymers where a branched alkyl side chain is gradually exchanged for a linear ethylene glycol based side chain. A series of random copolymers are prepared with glycol side chain percentages of 0, 10, 25, 50, 75, 90 and 100 with respect to the alkyl side chains. These are characterized in order to study the influence of the polar side chains on interaction with aqueous electrolytes, their electrochemical redox reactions and performance in OECTs when operated in aqueous electrolytes. We observe that glycol side chain percentages of >50 % are required to achieve volumetric charging while lower glycol chain percentages show a mixed operation with high required voltages to allow for bulk charging of the organic semiconductor. A strong dependence of the electron mobility on the fraction of glycol chains was found for copolymers based on NDI-T2, with a significant drop as alkyl side chains are replaced by glycol side chains.
McCulloch I, 2018, Non-fullerene acceptors for high performance organic photovoltaics, 10th International Conference on Hybrid and Organic Photovoltaics, Publisher: Fundació Scito
Kiefer D, Giovannitti A, Sun H, et al., 2018, Enhanced n-Doping Efficiency of a Naphthalenediimide-Based Copolymer through Polar Side Chains for Organic Thermoelectrics, ACS ENERGY LETTERS, Vol: 3, Pages: 278-285, ISSN: 2380-8195
Kiefer D, Giovannitti A, Sun H, et al., 2018, Enhanced n-Doping Efficiency of a Naphthalenediimide-Based Copolymer through Polar Side Chains for Organic Thermoelectrics., ACS Energy Lett, Vol: 3, Pages: 278-285, ISSN: 2380-8195
N-doping of conjugated polymers either requires a high dopant fraction or yields a low electrical conductivity because of their poor compatibility with molecular dopants. We explore n-doping of the polar naphthalenediimide-bithiophene copolymer p(gNDI-gT2) that carries oligoethylene glycol-based side chains and show that the polymer displays superior miscibility with the benzimidazole-dimethylbenzenamine-based n-dopant N-DMBI. The good compatibility of p(gNDI-gT2) and N-DMBI results in a relatively high doping efficiency of 13% for n-dopants, which leads to a high electrical conductivity of more than 10-1 S cm-1 for a dopant concentration of only 10 mol % when measured in an inert atmosphere. We find that the doped polymer is able to maintain its electrical conductivity for about 20 min when exposed to air and recovers rapidly when returned to a nitrogen atmosphere. Overall, solution coprocessing of p(gNDI-gT2) and N-DMBI results in a larger thermoelectric power factor of up to 0.4 μW K-2 m-1 compared to other NDI-based polymers.
Onwubiko N, McCulloch I, 2018, Fused electron deficient semiconducting polymers for air stable electron transport, Nature Communications, Vol: 9, ISSN: 2041-1723
Conventional semiconducting polymer synthesis typically involves transition metal mediated coupling reactions that link aromatic units with single bonds along the backbone. Rotation around these bonds contributes to conformational and energetic disorder and therefore potentially limits charge delocalization, whereas the use of transition metals present difficulties for sustainability and application in biological environments. We show that a simple aldol condensation reaction can prepare polymers where double bonds lock-in a rigid backbone conformation, thus eliminating free rotation along the conjugated backbone. This polymerization route requires neither organometallic monomers nor transition metal catalysts and offers a reliable design strategy to facilitate delocalization of frontier molecular orbitals, elimination of energetic disorder arising from rotational torsion and allowing closer interchain electronic coupling. These characteristics are desirable for high charge carrier mobilities. Our polymers with a high electron affinity display long wavelength NIR absorption with air stable electron transport in solution processed organic thin film transistors.
Cha H, Wheeler S, Holliday S, et al., 2018, Influence of blend morphology and energetics on charge separation and recombination dynamics in organic solar cells incorporating a nonfullerene acceptor, Advanced Functional Materials, Vol: 28, ISSN: 1616-301X
Nonfullerene acceptors (NFAs) in blends with highly crystalline donor polymers have been shown to yield particularly high device voltage outputs, but typically more modest quantum yields for photocurrent generation as well as often lower fill factors (FF). In this study, we employ transient optical and optoelectronic analysis to elucidate the factors determining device photocurrent and FF in blends of the highly crystalline donor polymer PffBT4T-2OD with the promising NFA FBR or the more widely studied fullerene acceptor PC71BM. Geminate recombination losses, as measured by ultrafast transient absorption spectroscopy, are observed to be significantly higher for PffBT4T-2OD:FBR blends. This is assigned to the smaller LUMO-LUMO offset of the PffBT4T-2OD:FBR blends relative to PffBT4T-2OD:PC71BM, resulting in the lower photocurrent generation efficiency obtained with FBR. Employing time delayed charge extraction measurements, these geminate recombination losses are observed to be field dependent, resulting in the lower FF observed with PffBT4T-2OD:FBR devices. These data therefore provide a detailed understanding of the impact of acceptor design, and particularly acceptor energetics, on organic solar cell performance. Our study concludes with a discussion of the implications of these results for the design of NFAs in organic solar cells.
Tan CH, Gorman J, Wadsworth A, et al., 2018, Barbiturate end-capped non-Fullerene acceptors for organic solar cells: tuning acceptor energetics to suppress geminate recombination losses, Chemical Communications, Vol: 54, Pages: 2966-2969, ISSN: 1359-7345
We report the synthesis of two barbiturate end-capped non-fullerene acceptors and demonstrate their efficient function in high voltage output organic solar cells. The acceptor with the lower LUMO level is shown to exhibit suppressed geminate recombination losses, resulting in enhanced photocurrent generation and higher overall device efficiency.
Chen H-Y, Nikolka M, Wadsworth A, et al., 2018, A Thieno[2,3-b]pyridine-Flanked Diketopyrrolopyrrole Polymer as an n-Type Polymer Semiconductor for All-Polymer Solar Cells and Organic Field-Effect Transistors, MACROMOLECULES, Vol: 51, Pages: 71-79, ISSN: 0024-9297
Wadsworth A, Baran D, Gorman J, et al., 2018, CHAPTER 3: High-performance Organic Photovoltaic Donor Polymers, RSC Nanoscience and Nanotechnology, Pages: 69-108, ISBN: 9781788010801
The field of organic photovoltaics has advanced a great deal over the last decade, with device efficiencies now exceeding 11%. A large part of this success can be attributed to the development of donor polymer materials, from their humble beginnings as homopolymers to the highly tuned push-pull copolymer and terpolymer materials that are now being reported on a regular basis. Through the careful use of chemical modification, it has been possible to design and synthesize a wide variety of donor polymers, allowing optimization of both the optoelectronic and structural properties of the materials. In doing so, more favourable active layer blends have been achieved and therefore significant improvements in device performance have been observed. Herein we discuss how the chemical design of donor polymers for organic photovoltaics has led to the emergence of high-performance materials.
Wadsworth A, Hamid Z, Bidwell M, et al., 2018, Progress in Poly (3-Hexylthiophene) Organic Solar Cells and the Influence of Its Molecular Weight on Device Performance, ADVANCED ENERGY MATERIALS, Vol: 8, ISSN: 1614-6832
McCulloch I, 2018, Synthesis and Characterisation of Non-Fullerene Electron Acceptors for Organic Photovoltaics Doctoral Thesis accepted by the Imperial College London, UK Supervisor's Foreword, SYNTHESIS AND CHARACTERISATION OF NON-FULLERENE ELECTRON ACCEPTORS FOR ORGANIC PHOTOVOLTAICS, Publisher: SPRINGER INTERNATIONAL PUBLISHING AG, Pages: V-V, ISBN: 978-3-319-77090-1
Pace NA, Zhang W, Arias DH, et al., 2017, Controlling Long-Lived Triplet Generation from Intramolecular Singlet Fission in the Solid State, JOURNAL OF PHYSICAL CHEMISTRY LETTERS, Vol: 8, Pages: 6086-6091, ISSN: 1948-7185
Moia D, Giovannitti A, Szumska AA, et al., 2017, A salt water battery with high stability and charging rates made from solution processed conjugated polymers with polar side chains, Publisher: arXiv
We report a neutral salt water based battery which uses p-type and n-typesolution processed polymer films as the cathode and the anode of the cell. Thespecific capacity of the electrodes (approximately 30 mAh cm-3) is achieved viaformation of bipolarons in both the p-type and n-type polymers. By engineeringethylene glycol and zwitterion based side chains attached to the polymerbackbone we facilitate rapid ion transport through the non-porous polymerfilms. This, combined with efficient transport of electronic charge via theconjugated polymer backbones, allowed the films to maintain constant capacityat high charge and discharge rates (>1000 C-rate). The electrodes also showgood stability during electrochemical cycling (less than 30% decrease incapacity over >1000 cycles) and an output voltage up to 1.4 V. The performanceof these semiconducting polymers with polar side-chains demonstrates thepotential of this material class for fast-charging, water based electrochemicalenergy storage devices.
Gasparini N, Salvador M, Heumueller T, et al., 2017, Polymer:Nonfullerene Bulk Heterojunction Solar Cells with Exceptionally Low Recombination Rates, ADVANCED ENERGY MATERIALS, Vol: 7, ISSN: 1614-6832
Zhang Y, Li J, Li R, et al., 2017, Liquid-Solid Dual-Gate Organic Transistors with Tunable Threshold Voltage for Cell Sensing, ACS APPLIED MATERIALS & INTERFACES, Vol: 9, Pages: 38687-38694, ISSN: 1944-8244
Gasparini N, Salvador M, Strohm S, et al., 2017, Burn-in Free Nonfullerene-Based Organic Solar Cells, ADVANCED ENERGY MATERIALS, Vol: 7, ISSN: 1614-6832
Bregadiolli BA, Ramanitra HH, Ferreira RM, et al., 2017, Towards the synthesis of poly(azafulleroid)s: main chain fullerene oligomers for organic photovoltaic devices, POLYMER INTERNATIONAL, Vol: 66, Pages: 1364-1371, ISSN: 0959-8103
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Chen H, Hurhangee M, Nikolka M, et al., 2017, Dithiopheneindenofluorene (<bold>TIF</bold>) Semiconducting Polymers with Very High Mobility in Field-Effect Transistors, ADVANCED MATERIALS, Vol: 29, ISSN: 0935-9648
Collado-Fregoso E, Hood SN, Shoaee S, et al., 2017, Intercalated vs Nonintercalated Morphologies in Donor-Acceptor Bulk Heterojunction Solar Cells: PBTTT:Fullerene Charge Generation and Recombination Revisited., Journal of Physical Chemistry Letters, Vol: 8, Pages: 4061-4068, ISSN: 1948-7185
In this Letter, we study the role of the donor:acceptor interface nanostructure upon charge separation and recombination in organic photovoltaic devices and blend films, using mixtures of PBTTT and two different fullerene derivatives (PC70BM and ICTA) as models for intercalated and nonintercalated morphologies, respectively. Thermodynamic simulations show that while the completely intercalated system exhibits a large free-energy barrier for charge separation, this barrier is significantly lower in the nonintercalated system and almost vanishes when energetic disorder is included in the model. Despite these differences, both femtosecond-resolved transient absorption spectroscopy (TAS) and time-delayed collection field (TDCF) exhibit extensive first-order losses in both systems, suggesting that geminate pairs are the primary product of photoexcitation. In contrast, the system that comprises a combination of fully intercalated polymer:fullerene areas and fullerene-aggregated domains (1:4 PBTTT:PC70BM) is the only one that shows slow, second-order recombination of free charges, resulting in devices with an overall higher short-circuit current and fill factor. This study therefore provides a novel consideration of the role of the interfacial nanostructure and the nature of bound charges and their impact upon charge generation and recombination.
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