Publications
641 results found
Knall A-C, Ashraf RS, Nikolka M, et al., 2016, Naphthacenodithiophene based polymers—new membersof the acenodithiophene family exhibiting high mobilityand power conversion efficiency, Advanced Functional Materials, Vol: 26, Pages: 6961-6969, ISSN: 1616-3028
Wide-bandgap conjugated polymers with a linear naphthacenodithiophene(NDT) donor unit are herein reported along with their performance in bothtransistor and solar cell devices. The monomer is synthesized starting from2,6-dihydroxynaphthalene with a double Fries rearrangement as the key step.By copolymerization with 2,1,3-benzothiadiazole (BT) via a palladium-catalyzedSuzuki coupling reaction, NDT-BT co-polymers with high molecular weightsand narrow polydispersities are afforded. These novel wide-bandgap polymersare evaluated as the semiconducting polymer in both organic field effect transistorand organic photovoltaic applications. The synthesized polymers revealan optical bandgap in the range of 1.8 eV with an electron affinity of 3.6 eVwhich provides sufficient energy offset for electron transfer to PC70BM acceptors.In organic field effect transistors, the synthesized polymers demonstratehigh hole mobilities of around 0.4 cm2 V–1 s–1. By using a blend of NDT-BTwith PC70BM as absorber layer in organic bulk heterojunction solar cells, powerconversion efficiencies of 7.5% are obtained. This value is among the highestobtained for polymers with a wider bandgap (larger than 1.7 eV), making thispolymer also interesting for application in tandem or multijunction solar cells.
Nielsen CBN, Giovannitti A, Sbircea DTS, et al., 2016, Molecular Design of Semiconducting Polymers for High-Performance Organic Electrochemical Transistors, Journal of the American Chemical Society, Vol: 138, Pages: 10252-10259, ISSN: 1520-5126
The organic electrochemical transistor (OECT), capable of transducing small ionic fluxes into electronic signals in anaqueous environment, is an ideal device to utilize in bioelectronic applications. Currently, most OECTs are fabricated with commerciallyavailable conducting poly(3,4-ethylenedioxythiophene) (PEDOT)-based suspensions and are therefore operated in depletionmode. Here, we present a series of semiconducting polymers designed to elucidate important structure-property guidelines requiredfor accumulation mode OECT operation. We discuss key aspects relating to OECT performance such as ion and hole transport,electrochromic properties, operational voltage and stability. The demonstration of our molecular design strategy is the fabrication ofaccumulation mode OECTs that clearly outperform state-of-the-art PEDOT based devices, and show stability under aqueous operationwithout the need for formulation additives and cross-linkers.
Vezie M, Few S, Meager I, et al., 2016, Exploring the origin of high optical absorption in conjugated polymers, Nature Materials, Vol: 15, Pages: 746-753, ISSN: 1476-4660
The specific optical absorption of an organic semiconductor is critical to the performance of organic optoelectronic devices. For example, higher light-harvesting efficiency can lead to higher photocurrent in solar cells that are limited by sub-optimal electrical transport. Here, we compare over 40 conjugated polymers, and find that many different chemical structures share an apparent maximum in their extinction coefficients. However, a diketopyrrolopyrrole-thienothiophene copolymer shows remarkably high optical absorption at relatively low photon energies. By investigating its backbone structure and conformation with measurements and quantum chemical calculations, we find that the high optical absorption can be explained by the high persistence length of the polymer. Accordingly, we demonstrate high absorption in other polymers with high theoretical persistence length. Visible light harvesting may be enhanced in other conjugated polymers through judicious design of the structure.
McCulloch I, Salleo A, Chabinyc M, 2016, Avoid the kinks when measuring mobility Transistor measurements can overstate organic semiconductor charge carrier mobility, Science, Vol: 352, Pages: 1521-1522, ISSN: 0036-8075
Holliday S, Ashraf RS, Wadsworth A, et al., 2016, High-efficiency and air-stable P3HT-based polymer solar cells with a new non-fullerene acceptor, Nature Communications, Vol: 7, Pages: 1-11, ISSN: 2041-1723
Solution-processed organic photovoltaics (OPV) offer the attractive prospect of low-cost, light-weight and environmentally benign solar energy production. The highest efficiency OPV at present use low-bandgap donor polymers, many of which suffer from problems with stability and synthetic scalability. They also rely on fullerene-based acceptors, which themselves have issues with cost, stability and limited spectral absorption. Here we present a new non-fullerene acceptor that has been specifically designed to give improved performance alongside the wide bandgap donor poly(3-hexylthiophene), a polymer with significantly better prospects for commercial OPV due to its relative scalability and stability. Thanks to the well-matched optoelectronic and morphological properties of these materials, efficiencies of 6.4% are achieved which is the highest reported for fullerene-free P3HT devices. In addition, dramatically improved air stability is demonstrated relative to other high-efficiency OPV, showing the excellent potential of this new material combination for future technological applications.
El Labban A, Chen H, Kirkus M, et al., 2016, Improved Efficiency in Inverted Perovskite Solar Cells Employing a Novel Diarylamino-Substituted Molecule as PEDOT:PSS Replacement, ADVANCED ENERGY MATERIALS, Vol: 6, ISSN: 1614-6832
Harkin DJ, Broch K, Schreck M, et al., 2016, Decoupling Charge Transport and Electroluminescence in a High Mobility Polymer Semiconductor, Advanced Materials, Vol: 28, Pages: 6378-6385, ISSN: 1521-4095
Fluorescence enhancement of a high mobility polymer semiconductor is achieved via energy transfer to a higher fluorescence quantum yield squaraine dye molecule on 50 ps timescales. In organic light emitting diodes an order of magnitude enhancement of the external quantum efficiency is observed without reduction in the charge carrier mobility resulting in radiances of up to 5 W str(-1) m(-2) at 800 nm.
Chen H, Bryant D, Troughton J, et al., 2016, One-Step Facile Synthesis of a Simple Hole Transport Material for Efficient Perovskite Solar Cells, Chemistry of Materials, Vol: 28, Pages: 2515-2518, ISSN: 1520-5002
McCulloch I, 2016, Semiconducting polymers and small molecules for transistors and solar cells, Publisher: AMER CHEMICAL SOC, ISSN: 0065-7727
Kassar T, Gueldal NS, Berlinghof M, et al., 2016, Real-Time Investigation of Intercalation and Structure Evolution in Printed Polymer:Fullerene Bulk Heterojunction Thin Films, ADVANCED ENERGY MATERIALS, Vol: 6, ISSN: 1614-6832
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- Citations: 17
Ramanitra HH, Silva HS, Bregadiolli BA, et al., 2016, Synthesis of Main-Chain Poly(fullerene)s from a Sterically Controlled Azomethine Ylide Cycloaddition Polymerization, MACROMOLECULES, Vol: 49, Pages: 1681-1691, ISSN: 0024-9297
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- Citations: 16
Held M, Zakharko Y, Wang M, et al., 2016, Photo- and electroluminescence of ambipolar, high-mobility, donor-acceptor polymers, Organic Electronics, Vol: 32, Pages: 220-227, ISSN: 1566-1199
Donor-acceptor polymers with narrow bandgaps are promising materials for bulk heterojunction solar cells and high-mobility field-effect transistors. They also emit light in the near-infrared. Here we investigate and compare the photoluminescence and electroluminescence properties of different narrow bandgap (<1.5 eV) donor-acceptor polymers with diketopyrrolopyrrole (DPP), isoindigo (IGT) and benzodipyrrolidone (BPT) cores, respectively. All of them show near-infrared photoluminescence quantum yields of 0.03–0.09% that decrease with decreasing bandgap. Bottom-contact/top-gate field-effect transistors show ambipolar charge transport with hole and electron mobilities between 0.02 and 0.7 cm2 V−1 s−1 and near-infrared electroluminescence. Their external quantum efficiencies reach up to 0.001%. The effect of polaron quenching and other reasons for the low electroluminescence efficiency of these high mobility polymers are investigated.
Ramadan AJ, Nielsen CB, Holliday S, et al., 2016, Organic/inorganic epitaxy: commensurate epitaxial growth of truxenone on Cu (111), RSC Advances, Vol: 6, Pages: 17125-17128, ISSN: 2046-2069
Dimitrov SD, Schroeder BC, Nielsen CB, et al., 2016, Singlet Exciton Lifetimes in Conjugated Polymer Films for Organic Solar Cells, Polymers, Vol: 8, ISSN: 2073-4360
The lifetime of singlet excitons in conjugated polymer films is a key factor taken into account during organic solar cell device optimization. It determines the singlet exciton diffusion lengths in polymer films and has a direct impact on the photocurrent generation by organic solar cell devices. However, very little is known about the material properties controlling the lifetimes of singlet excitons, with most of our knowledge originating from studies of small organic molecules. Herein, we provide a brief summary of the nature of the excited states in conjugated polymer films and then present an analysis of the singlet exciton lifetimes of 16 semiconducting polymers. The exciton lifetimes of seven of the studied polymers were measured using ultrafast transient absorption spectroscopy and compared to the lifetimes of seven of the most common photoactive polymers found in the literature. A plot of the logarithm of the rate of exciton decay vs. the polymer optical bandgap reveals a medium correlation between lifetime and bandgap, thus suggesting that the Energy Gap Law may be valid for these systems. This therefore suggests that small bandgap polymers can suffer from short exciton lifetimes, which may limit their performance in organic solar cell devices. In addition, the impact of film crystallinity on the exciton lifetime was assessed for a small bandgap diketopyrrolopyrrole co-polymer. It is observed that the increase of polymer film crystallinity leads to reduction in exciton lifetime and optical bandgap again in agreement with the Energy Gap Law.
Hayes SC, Pieridou G, Vezie M, et al., 2016, Effect of molecular weight on the vibronic structure of a diketopyrrolopyrrole polymer, Conference on Physical Chemistry of Interfaces and Nanomaterials XV, Publisher: SPIE-INT SOC OPTICAL ENGINEERING, ISSN: 0277-786X
Giovannitti A, McCulloch I, Nielsen C, et al., 2015, Sodium and potassium ion selective conjugated polymers for optical ion detection in solution and solid state, Advanced Functional Materials, Vol: 26, Pages: 514-523, ISSN: 1616-3028
This paper presents the development of alkali metal ion selective small molecules and conjugated polymers for optical ion sensing. A crown ether bithiophene unit was chosen as the detecting unit, as both a small molecule and incorporated into a conjugated aromatic structure. The complex formation and the resulting backbone twist of the detector unit was investigated by UV Vis and NMR spectroscopy where a remarkable selectivity towards sodium or potassium ions was found. X-Ray diffraction analysis of single crystals with and without alkali metal ions was carried out and a difference of the dihedral angle of more than 70 ° was observed. In a conjugated polymer structure, the detector unit has a higher sensitivity for alkali metal ion detection than its small molecule analogue. Ion selectivity was retained in polymers with solubility in polar solvents facilitated by the attachment of polar ethylene glycol side chains. This design concept was further evolved to develop a sodium-salt solid state sensor based on blends of the detecting polymer with a polyvinyl alcohol matrix where the detection of sodium ions was achieved in aqueous salt solutions with concentrations similar to biological important environments.
Snyder CR, Kline RJ, DeLongchamp DM, et al., 2015, Classification of Semiconducting Polymeric Mesophases to Optimize Device Postprocessing, JOURNAL OF POLYMER SCIENCE PART B-POLYMER PHYSICS, Vol: 53, Pages: 1641-1653, ISSN: 0887-6266
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- Citations: 24
Freeman DME, Minotto A, Duffy W, et al., 2015, Highly red-shifted NIR emission from a novel anthracene conjugated polymer backbone containing Pt(II) porphyrins, Polymer Chemistry, Vol: 7, Pages: 722-730, ISSN: 1759-9954
We present the synthesis of a novel diphenylanthracene (DPA) based semiconducting polymer. The polymer is solubilised by alkoxy groups attached directly to a DPA monomer, meaning the choice of co-monomer is not limited to exclusively highly solubilising moieties. Interestingly, the polymer shows a red-shifted elecroluminescence maximum (510 nm) when compared to its photoluminescence maximum (450 nm) which we attribute to excimer formation. The novel polymer was utilised as a host for a covalently-linked platinum(II) complexed porphyrin dopant. Emission from these polymers was observed in the NIR and again showed almost a 100 nm red shift from photoluminescence to electroluminescence. This work demonstrates that utilising highly aggregating host materials is an effective tool for inducing red-shifted emission in OLEDs.
Heeney MJ, Han Y, Fei Z, et al., 2015, A Novel Alkylated Indacenodithieno[3,2-b]thiophene-based Polymer for High-performance Field Effect Transistors, Advanced Materials, Vol: 28, Pages: 3922-3927, ISSN: 1521-4095
A novel rigid donor monomer, indacenodithieno[3,2-b]thiophene (IDTT), containing linear alkyl chains is reported. Its copolymer with benzothiadiazole is an excellent p-type semiconductor, affording a mobility of 6.6 cm² V⁻¹ s⁻¹ in top-gated field-effect transistors with pentafluorobenzenethiol-modified Au electrodes. Electrode treatment with solution-deposited copper(I) thiocyanate (CuSCN) has a beneficial hole-injection/electron-blocking effect, further enhancing the mobility to 8.7 cm² V⁻¹ s⁻¹.
Nielsen CB, Holliday S, Chen H, et al., 2015, Non-fullerene electron acceptors for use in organic solar cells, Accounts of Chemical Research, Vol: 48, Pages: 2803-2812, ISSN: 1520-4898
The active layer in a solution processed organic photovoltaic device comprises a light absorbing electron donor semiconductor, typically a polymer, and an electron accepting fullerene acceptor. Although there has been huge effort targeted to optimize the absorbing, energetic, and transport properties of the donor material, fullerenes remain as the exclusive electron acceptor in all high performance devices. Very recently, some new non-fullerene acceptors have been demonstrated to outperform fullerenes in comparative devices. This Account describes this progress, discussing molecular design considerations and the structure–property relationships that are emerging.The motivation to replace fullerene acceptors stems from their synthetic inflexibility, leading to constraints in manipulating frontier energy levels, as well as poor absorption in the solar spectrum range, and an inherent tendency to undergo postfabrication crystallization, resulting in device instability. New acceptors have to address these limitations, providing tunable absorption with high extinction coefficients, thus contributing to device photocurrent. The ability to vary and optimize the lowest unoccupied molecular orbital (LUMO) energy level for a specific donor polymer is also an important requirement, ensuring minimal energy loss on electron transfer and as high an internal voltage as possible. Initially perylene diimide acceptors were evaluated as promising acceptor materials. These electron deficient aromatic molecules can exhibit good electron transport, facilitated by close packed herringbone crystal motifs, and their energy levels can be synthetically tuned. The principal drawback of this class of materials, their tendency to crystallize on too large a length scale for an optimal heterojunction nanostructure, has been shown to be overcome through introduction of conformation twisting through steric effects. This has been primarily achieved by coupling two units together, forming dimers
Baran D, Vezie MS, Gasparini N, et al., 2015, Role of Polymer Fractionation in Energetic Losses and Charge Carrier Lifetimes of Polymer: Fullerene Solar Cells, JOURNAL OF PHYSICAL CHEMISTRY C, Vol: 119, Pages: 19668-19673, ISSN: 1932-7447
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- Citations: 20
Yue W, Ashraf RS, Nielsen C, et al., 2015, A Thieno[3,2-b][1]benzothiophene Isoindigo Building Block for Additive- and Annealing-Free High-Performance Polymer Solar Cells, Advanced Materials, Vol: 27, Pages: 4702-4707, ISSN: 1521-4095
A novel photoactive polymer with two different molecular weights is reported, based on a new building block: thieno[3,2-b][1]benzothiophene isoindigo. Due to the improved crystallinity, optimal blend morphology, and higher charge mobility, solar-cell devices of the high-molecular-weight polymer exhibit a superior performance, affording efficiencies of 9.1% without the need for additives, annealing, or additional extraction layers during device fabrication.
Schroeder BC, Kirkus M, Nielsen CB, et al., 2015, Dithienosilolothiophene: A New Polyfused Donor for Organic Electronics, MACROMOLECULES, Vol: 48, Pages: 5557-5562, ISSN: 0024-9297
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- Citations: 3
Andemach R, Utzat H, Dimitrov SD, et al., 2015, Synthesis and Exciton Dynamics of Triplet Sensitized Conjugated Polymers, JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, Vol: 137, Pages: 10383-10390, ISSN: 0002-7863
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- Citations: 39
Fallon KJ, Wijeyasinghe N, Yaacobi-Gross N, et al., 2015, A Nature-Inspired Conjugated Polymer for High Performance Transistors and Solar Cells, MACROMOLECULES, Vol: 48, Pages: 5148-5154, ISSN: 0024-9297
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- Citations: 46
Schroeder BC, Nielsen CB, Westacott P, et al., 2015, Effects of alkyl chain positioning on conjugated polymer microstructure and field-effect mobilities, MRS Communications, Vol: 5, Pages: 435-440, ISSN: 2159-6867
Gomes HL, Medeiros MCR, Villani F, et al., 2015, All-inkjet printed organic transistors: Dielectric surface passivation techniques for improved operational stability and lifetime, MICROELECTRONICS RELIABILITY, Vol: 55, Pages: 1192-1195, ISSN: 0026-2714
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- Citations: 22
Wade J, Wood S, Beatrup D, et al., 2015, Operational electrochemical stability of thiophene-thiazole copolymers probed by resonant Raman spectroscopy., Journal of Chemical Physics, Vol: 142, Pages: 244904-244904, ISSN: 1089-7690
We report on the electrochemical stability of hole polarons in three conjugated polymers probed by resonant Raman spectroscopy. The materials considered are all isostructural to poly(3-hexyl)thiophene, where thiazole units have been included to systematically deepen the energy level of the highest occupied molecular orbital (HOMO). We demonstrate that increasing the thiazole content planarizes the main conjugated backbone of the polymer and improves the electrochemical stability in the ground state. However, these more planar thiazole containing polymers are increasingly susceptible to electrochemical degradation in the polaronic excited state. We identify the degradation mechanism, which targets the C=N bond in the thiazole units and results in disruption of the main polymer backbone conjugation. The introduction of thiazole units to deepen the HOMO energy level and increase the conjugated backbone planarity can be beneficial for the performance of certain optoelectronic devices, but the reduced electrochemical stability of the hole polaron may compromise their operational stability.
Rumer JW, Ashraf RS, Eisenmenger ND, et al., 2015, Dual Function Additives: A Small Molecule Crosslinker for Enhanced Efficiency and Stability in Organic Solar Cells, ADVANCED ENERGY MATERIALS, Vol: 5, ISSN: 1614-6832
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- Citations: 61
Andernach RE, Rossbauer S, Ashraf RS, et al., 2015, Conjugated Polymer-Porphyrin Complexes for Organic Electronics, CHEMPHYSCHEM, Vol: 16, Pages: 1223-1230, ISSN: 1439-4235
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- Citations: 11
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