Studies are reported on a series of triphenylamine–(C≡C)n–2,5-diphenyl-1,3,4-oxadiazole dyad molecules (1, 2, 3 and 4; n = 1-4, respectively) and the related triphenylamine–C6H4–(C≡C)3–oxadiazole dyad 5. The oligoynelinked D––A dyad systems have been synthesized by palladium-catalyzed cross-coupling of terminal alkynyl and butadiynyl synthons with the corresponding bromoalkynyl moieties. Cyclic voltammetric studies reveal a reduction in the HOMO-LUMO gap in the series of compounds 1–4 as the oligoyne chain length increases which is consistent with extended conjugation through the elongated bridges. Photophysical studies provide new insights into conjugative effects in oligoyne molecular wires. In non-polar solvents the emission from these dyad systems has two different origins: a locally excited (LE) state which is responsible for a  fluorescence and an intramolecular charge transfer (ICT) state which produces charge transfer emission. In polar solvents the LE state emission vanishes and only ICT emission is observed. This emission displays strong solvatochromism and analysis according to the LippertMataga-Oshika formalism shows significant ICT for all the luminescent compounds with high efficiency even for the longer more conjugated systems. The excited state properties of the dyads in non-polar solvents vary with the extent of conjugation. For more conjugated systems a fast non-radiative route dominates the excited state decay and follows the Engelman-Jortner energy gap law. The data suggest that the non-radiative decay is driven by the weak coupling limit. LOP-Version13/07/2009 File: Artic-65.doc

Post-polymerization modification of the donor-acceptor polymer, poly(9,9-dioctylfluorene-alt-benzothiadiazole), PF8-BT, by electrophilic C-H borylation is a simple method to introduce controllable quantities of near-infrared (near-IR) emitting chromophore units into the backbone of a conjugated polymer. The highly stable borylated unit possesses a significantly lower LUMO energy than the pristine polymer resulting in a reduction in the band gap of the polymer by up to 0.63 eV and a red shift in emission of more than 150 nm. Extensively borylated polymers absorb strongly in the deep red/near-IR and are highly emissive in the near-IR region of the spectrum in solution and solid state. Photoluminescence quantum yield (PLQY) values are extremely high in the solid state for materials with emission maxima ≥ 700 nm with PLQY values of 44% at 700 nm and 11% at 757 nm for PF8-BT with different borylation levels. This high brightness enables efficient solution processed near-IR emitting OLEDs to be fabricated and highly emissive borylated polymer loaded conjugated polymer nanoparticles (CPNPs) to be prepared. The latter are bright, photostable, low toxicity bioimaging agents that in phantom mouse studies show higher signal to background ratios for emission at 820 nm than the ubiquitous near-IR emissive bioimaging agent indocyanine green. This methodology represents a general approach for the post-polymerization functionalization of donor-acceptor polymers to reduce the band gap as confirmed by the C-H borylation of poly((9,9-dioctylfluorene)-2,7-diyl-alt-[4,7-bis(3-hexylthien-5-yl)-2,1,3-benzothiadiazole]-2c,2cc-diyl) (PF8TBT) resulting in a red shift in emission of >150 nm, thereby shifting the emission maximum to 810 nm.

A method to print two materials of different functionality during the same printing step is presented. In printed electronics, devices are built layer by layer and conventionally only one type of material is deposited in one pass. Here, the challenges involving printing of two emissive materials to form polymer light-emitting diodes (PLEDs) that emit light of different wavelengths without any significant changes in the device characteristics are described. The surface-energy-patterning technique is utilized to print materials in regions of interest. This technique proves beneficial in reducing the amount of ink used during blade coating and improving the reproducibility of printed films. A variety of colors (green, red, and near-infrared) are demonstrated and characterized. This is the first known attempt to print multiple materials by blade coating. These devices are further used in conjunction with a commercially available photodiode to perform blood oxygenation measurements on the wrist, where common accessories are worn. Prior to actual application, the threshold conditions for each color are discussed, in order to acquire a stable and reproducible photoplethysmogram (PPG) signal. Finally, based on the conditions, PPG and oxygenation measurements are successfully performed on the wrist with green and red PLEDs.

The microstructure of blend films of conjugated polymer and fullerene, especially the degree of mixing and crystallization, impacts the performance of organic photovoltaic devices considerably. Mixing and crystallization affect device performance in different ways. These phenomena are not easy to screen using traditional methods such as imaging. In this paper, the amorphous regiorandom poly(3‐hexylthiophene) is blended with the potentially crystalline fullerene [6,6]‐phenyl‐C 61 ‐butyric acid methyl ester PCBM and the amorphous bis‐adduct. First, the degree of mixing of polymer: fullerene blends is evaluated using UV–Vis absorption, steady‐state and ultra‐fast photoluminescence spectroscopy. The blue‐shift of the polymer emission and absorption onset are used in combination with the saturation of the polymer emission decay time upon fullerene addition in order to infer the onset of aggregation of the blends. Second, the crystallinity of the fullerene is probed using variable angle spectroscopic ellipsometry (VASE), electroluminescence and photoluminescence spectroscopy. It is shown that the red‐shift of charge transfer emission in the case of PCBM based blends cannot be explained solely by a variation of optical dielectric constant as probed by VASE. A combination of optical spectroscopy techniques, therefore, allows to probe the degree of mixing and can also distinguish between aggregation and crystallization of fullerenes.

Three diaminodicyanoquinodimethanes, 4-(R(1)R(2)C)-1-[(NC)2C]-C6H4 (R(1),R(2) = H2N, 1; R(1) = 3,5-Me2-4-OCH4H6N-, R(2) = H2N, 2; R(1) = 3,5-Me2-4-OCH4H6N-, R(2) = 4-Me-C5H9N, 3), were investigated using carbon-13 NMR, steady-state, and ultrafast transient absorption and ultrafast fluorescence spectroscopies to unravel the unusual characteristics of this class of chromophores. Computed (GIAO)B3LYP/6-31G* data for the zwitterions 1-3 using necessary solvation (PCM) models were shown to be in excellent agreement with observed structural and carbon-13 NMR data. The ground-state geometries of 1-3 contain a cationic methine group R(1)R(2)C- twisted from the C6H4 ring and an anionic methine group (NC)2C- in plane with the C6H4 ring in solution and solid state. The (13)C chemical shifts of the peak corresponding to the methine carbon at the (NC)2C- group of 1-3 are observed at 32.5-34.7 ppm, which are some 55 ppm upfield compared with the (13)C chemical shift for the methine carbons in TCNQ, 1,4-[(NC)2C]2-C6H4. The decay of the excited state in diaminodicyanoquinodimethanes is fast and dominated by nonradiative processes on the picosecond time scale, which depends on the viscosity of the medium. The dynamics of the excited-state decay is therefore limited by conformational changes through an intramolecular twisting motion. This twisting motion is hindered by friction, which, in turn, also depends on the functional group size of the system. The dominant nonradiative pathways after excitation are due to twisted excited-state conformers according to TD-DFT computations.

ABSTRACT We present a study of the optical, structural and device properties of a polyfluorene (PFM)‐based (PFM‐F8BT‐PFM) donor–acceptor triblock copolymer for use in an organic solar cell. Neutron reflectivity is employed to probe the vertical composition profile before and after thermal annealing while the crystallinity was examined using grazing incidence wide‐angle X‐ray. The absorption spectra and photoluminescence emission for the triblock and analogous blend of PFM with F8BT reveal a greater degree of intermixing in the triblock. However, the triblock copolymer exhibits exciplex emission, which necessitates a geminate polar pair; long‐lived exciplex states are detrimental in organic photovoltaic devices. The triplet yield in the triblock and the blend is estimated using photoinduced absorption, with the triblock copolymer generating a triplet population 20 times that of the blend. This is far from ideal as triplets are wasted states in organic photovoltaic devices and they can also act as scavengers of polarons reducing the efficiency even more. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2013 , 51 , 1705–1718

We investigate the relationship between processing parameters and the device performance of gravure printed organic solar cells. Ink viscosity, surface energy and surface roughness are studied to optimise the printing process. Surfactants, additives and surface modification by plasma cleaning are utilised to achieve homogeneous printing of multilayer OPV device architectures. It is found that use of high boiling point solvents with high solubilities leads to a desirable surface morphology. The use of a printed metal oxide electrode within the inverted structure leads to devices with lifetimes exceeding those of devices in standard structures without the need for encapsulation.

We demonstrate that blend films containing poly(3-hexylthiophene-2,5-diyl) and in situ grown CdS display a greater yield of photogenerated charges than a blend containing an equivalent amount of pre-synthesised CdS quantum dots. Moreover, we show that the greater charge yield in the in situ grown films leads to an improvement in device efficiency. The present findings also appear to suggest that charge photogeneration at the CdS/polymer heterojunction is facilitated by the formation of nanoparticle networks as a result of CdS aggregation.

The bis and tris adducts of [6,6]phenyl-C61-butyric acid methyl ester (PCBM) offer lower reduction potentials than PCBM and are therefore expected to offer larger open-circuit voltages and more efficient energy conversion when blended with conjugated polymers in photovoltaic devices in place of PCBM. However, poor photovoltaic device performances are commonly observed when PCBM is replaced with higher-adduct fullerenes. In this work, we use transmission electron microscopy (TEM), steady-state and ultrafast time-resolved photoluminescence spectroscopy (PL), and differential scanning calorimetry (DSC) to probe the microstructural properties of blend films of poly(3-hexylthiophene-2,5-diyl) (P3HT) with the bis and tris adducts of PCBM. TEM and PL indicate that, in as-spun blend films, fullerenes become less soluble in P3HT as the number of adducts increases. PL indicates that upon annealing crystallization leads to phase separation in P3HT:PCBM samples only. DSC studies indicate that the interactions between P3HT and the fullerene become weaker with higher-adduct fullerenes and that all systems exhibit eutectic phase behavior with a eutectic composition being shifted to higher molar fullerene content for higher-adduct fullerenes. We propose two different mechanisms of microstructure development for PCBM and higher-adduct fullerenes. P3HT:PCBM blends, phase segregation is the result of crystallization of either one or both components and is facilitated by thermal treatments. In contrast, for blends containing higher adducts, the phase separation is due to a partial demixing of the amorphous phases. We rationalize the lower photocurrent generation by the higher-adduct fullerene blends in terms of film microstructure.

The photophysics of a homopolymer containing pendant phenoxy-benzothiadiazole-bis(thiophene) (OPhBTDT2) moieties, a block copolymer containing both OPhBTDT2 and triphenylamine-based (TPA) pendant units, and a benzothiadiazole model compound, were investigated using steady-state and time-resolved photo-spectroscopic techniques, and quantum mechanical calculations. Electronic excitation of the OPhBTDT2 chromophores leads to rapid intra-molecular charge re-distribution in the lowest unoccupied molecular orbital resulting in substantially increased electron density on the BTD component. In dilute fluid solution, the fluorescence lifetime of the OPhBTDT2 moieties in the block co-polymer was partially quenched due to photo-oxidation of TPA. The triplet excited-state lifetime of the OPhBTDT2 groups in the block co-polymer in solution was unaffected by the TPA moieties signifying that triplet excited-state OPhBTDT2 groups do not oxidize the TPA moieties. In spin-cast films, the OPhBTDT2 singlet and triplet excitons are shorter-lived than the corresponding excited states of the polymers or the OPhBTDT2 model compound in dilute solution, and the lifetimes are essentially independent of the presence of the TPA groups in the block co-polymer. This quenching of OPhBTDT2 exciton lifetimes in the films suggests efficient non-radiative energy migration to low-energy traps, possibly non-emissive OPhBTDT2 molecular aggregates. The complete quenching of fluorescence from OPhBTDT2 in a 1:1 blend of the OPhBTDT2 homoploymer and the electron acceptor [6,6]-phenyl C-61 butyric acid methyl ester (PC61BM) is attributed to efficient photo-induced reduction of PC61BM by OPhBTDT2 singlet excitons based on evidence for radical ion formation obtained from nanosecond transient absorbance measurements. The decay kinetics of the absorbance by the resulting charge carriers is consistent with a slow, trap-limited bimolecular recombination mechanism, so the low performance of photovoltaic devices produced using the blend is thought to be limited by extensive phase separation and/or low hole mobility. Crown Copyright (C) 2011 Published by Elsevier B.V. All rights reserved.

Hybrid metal sulfide/polymer solar cell active layers are fabricated employing an approach based upon the in-situ thermal decomposition of a single source metal xanthate precursor in a semiconducting polymer film. The nanomorphology of the film, the charge photogeneration yield at the donor-acceptor heterojunction and device performance are shown to be dependent upon the annealing tern perature. Photovoltaic devices based upon such layers are shown to exhibit power conversion efficiencies of similar to 2.2% under AM1.5 solar illumination thus demonstrating the potential of such nanocomposite films for photovoltaic device applications.

ADVERTISEMENT RETURN TO ISSUEPREVCommunication to the...Communication to the EditorNEXTIndacenodithiophene-co-benzothiadiazole Copolymers for High Performance Solar Cells or Transistors via Alkyl Chain OptimizationHugo Bronstein†, Dong Seok Leem†, Richard Hamilton‡, Paul Woebkenberg†, Simon King†, Weimin Zhang†, Raja Shahid Ashraf†, Martin Heeney†, Thomas D. Anthopoulos†, John de Mello†, and Iain McCulloch*†View Author Information† Department of Chemistry, Centre for Plastic Electronics, Imperial College London, London SW7 2AZ, U.K.‡ Solar Press, 2 Royal College Sreet, London NW1 0NH, U.K.E-mail: [email protected]Cite this: Macromolecules 2011, 44, 17, 6649–6652Publication Date (Web):August 22, 2011Publication History Received20 May 2011Revised6 August 2011Published online22 August 2011Published inissue 13 September 2011https://pubs.acs.org/doi/10.1021/ma201158dhttps://doi.org/10.1021/ma201158drapid-communicationACS PublicationsCopyright © 2011 American Chemical SocietyRequest reuse permissionsArticle Views7017Altmetric-Citations163LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InRedditEmail Other access optionsGet e-AlertscloseSupporting Info (1)»Supporting Information Supporting Information SUBJECTS:Alkyls,Mobility,Nanospheres,Polymers,Thin films Get e-Alerts

Studies are reported on a series of triphenylamine-(C[triple bond]C)(n)-2,5-diphenyl-1,3,4-oxadiazole dyad molecules (n=1-4, 1, 2, 3 and 4, respectively) and the related triphenylamine-C(6)H(4)-(C[triple bond]C)(3)-oxadiazole dyad 5. The oligoyne-linked D-pi-A (D=electron donor, A=electron acceptor) dyad systems have been synthesised by palladium-catalysed cross-coupling of terminal alkynyl and butadiynyl synthons with the corresponding bromoalkynyl moieties. Cyclic voltammetric studies reveal a reduction in the HOMO-LUMO gap in the series of compounds 1-4 as the oligoyne chain length increases, which is consistent with extended conjugation through the elongated bridges. Photophysical studies provide new insights into conjugative effects in oligoyne molecular wires. In non-polar solvents the emission from these dyad systems has two different origins: a locally excited (LE) state, which is responsible for a pi*-->pi fluorescence, and an intramolecular charge transfer (ICT) state, which produces charge-transfer emission. In polar solvents the LE state emission vanishes and only ICT emission is observed. This emission displays strong solvatochromism and analysis according to the Lippert-Mataga-Oshika formalism shows significant ICT for all the luminescent compounds with high efficiency even for the longer more conjugated systems. The excited-state properties of the dyads in non-polar solvents vary with the extent of conjugation. For more conjugated systems a fast non-radiative route dominates the excited-state decay and follows the Engelman-Jortner energy gap law. The data suggest that the non-radiative decay is driven by the weak coupling limit.

The synthesis of a series of novel, unsymmetrically substituted benzothiadiazole-containing vinyl monomers and their free radical polymerization with and without the control of a reversible addition−fragmentation chain transfer (RAFT) agent is reported. The resulting polymers with electroactive pendants show tunable absorption and emission spectra depending on their molecular architecture. Using RAFT allows the synthesis of block copolymers using a hole-transporting vinyl-triarylamine as a second monomer. Efficient energy transfer between the two pendants has been detected. Cyclic voltammetry and photoelectron spectroscopy in air measurements have been employed to reveal the location of the HOMO and LUMO of the block copolymers. The block copolymers also influence the morphology of spin-casted films and show rectifying behavior in organic photovoltaic devices.

Nanostructured composites of inorganic and organic materials are attracting extensive interest for electronic and optoelectronic device applications. In this paper, we introduce a general method for the fabrication of metal sulfide nanoparticle/polymer films employing a low-cost and low temperature route compatible with large-scale device manufacturing. Our approach is based upon the controlled in situ thermal decomposition of a solution processable metal xanthate precursor complex in a semiconducting polymer film. To demonstrate the versatility of our method, we fabricate a CdS/P3HT nanocomposite film and show that the metal sulfide network inside the polymer film assists in the absorption of visible light and enables the achievement of high yields of charge photogeneration at the CdS/P3HT heterojunction. Photovoltaic devices based upon such nanocomposite films show solar light to electrical energy conversion efficiencies of 0.7% under full AM1.5 illumination and 1.2% under 10% incident power, demonstrating the potential of such nanocomposite films for low-cost photovoltaic devices.

A series of donor-acceptor diblock copolymers with varying molecular weight are studied in thin film and compared with an 'equivalent' blend formed from donor and acceptor homopolymers. Steady-state and transient spectroscopies are used to demonstrate a correlation between low molecular weight block copolymers and increased photoluminescence quenching (up to 99%) leading to higher yields of long-lived free charges. Such block copolymers are shown, by electron microscopy, to exhibit phase-segregated micrdomains whose size and periodicity are determined by their molecular weight. Photovoltaic devices made using these materials show a peak efficiency of 0.11% and correlate with our spectroscopic results, subject to a trade-off between charge generation and tranpsort/collection.

The synthesis of easily functionalized and highly soluble fluorene-containing hexabenzocoronenes (FHBC) has been achieved in high yield at a gram scale. Conjugated triarylamine oligomers were coupled to the FHBC cores via Buchwald-Hartwig coupling, and the photophysical properties of resulting dendritic materials were examined by ultrafast laser spectroscopic techniques. Efficient quenching of the triarylamine oligomer fluorescence was observed paving the way for the inclusion of these materials in bulk heterojunction solar cells. In preliminary studies, solar cell devices with external quantum efficiencies above 5% have been fabricated.

A major potential difference between polymer and small molecule organic light-emitting devices is the possibility of spin-dependent charge recombination in the latter. In this case, the singlet exciton formation yield, one of the key parameters that determines device efficiencies, deviates from the simple quantum mechanical spin statistics prediction of 25%. For polymers, the departure from this limit has been demonstrated by several indirect measurements yielding a wide spread values from 25% up to 95% and by ourselves using a direct measurement on working devices at 44%. These results clearly indicate that polymer-based devices hold a unique advantage over small molecule-based devices. Comment will be made to these various measurement techniques along with an insight into current theoretical ideas that can explain the departure from the quantum spin statistical limit.

A description of the synthesis of random (9,9-dioctylfluorene-2,7-diyl)-dibenzothiophene-S,S-dioxide-3,7-diyl) co-polymers (p(F-S)x) by palladium- catalyzed Suzuki cross-coupling polymerization where the feed ration of the latter is varied from 2 to 30 mol % (i.e., x=2-30) is given. Polymer light emitting devices are fabricated with the configuration indium tin oxide/poly(3,4-ethylenediocythiophene):poly(styrenesulfonic acid)/p(F-S)x/Ba/Al. The device external quantum efficiency increased as the ration of the S co-monomer was increased, up to a maximum of 1.3% at 100 mA cm(-2) for p(F-S)30 and a brightness of 3 770 cd m(-2) (at 10V). The S units impart improved electron injection, more balanced mobilities, and markedly improved device performance compared to poly(9,9-dioctylflouorene) under similar conditions. These co-polymers display broad emission, observed as greenish-white light, which arises from dual fluorescence, viz. both local excited states and charge transfer states. Utilizing dual emission can reduce problems associated with Forster energy transfer from high-energy to-low energy excited states.

ADVERTISEMENT RETURN TO ISSUEPREVCommunication to the...Communication to the EditorNEXTA High Molecular Weight Aromatic PhOLED Matrix Polymer Obtained by Metal-Free, Superacid-Catalyzed PolyhydroxyalkylationM. Carmen G. Hernández, Mikhail G. Zolotukhin, Jose Luis Maldonado, Nina Rehmann, Klaus Meerholz, Simon King, Andrew P. Monkman, Nils Fröhlich, Christof J. Kudla, and Ullrich Scherf*View Author Information Instituto de Investigaciones en Materiales, Universidad Nacional Autonoma de Mexico, Apartado Postal 70-360, CU, Coyoacan 04510, Mexico D. F., Mexico Centro de Investigaciones en Óptica A.C. (CIO) Loma del Bosque # 115, Col. Lomas del Campestre, C.P. 37150, León Guanajuato, México Department of Chemistry, University of Cologne, Luxemburger Str. 116, D-50939 Cologne, Germany Department of Physics, Durham University, South Road, Durham DH1 3LE, U.K. Macromolecular Chemistry Group, Wuppertal University, Gauss-Str. 20, D-42097 Wuppertal, Germany *Corresponding author. E-mail: [email protected]Cite this: Macromolecules 2009, 42, 23, 9225–9230Publication Date (Web):November 10, 2009Publication History Received16 September 2009Revised30 October 2009Published online10 November 2009Published inissue 8 December 2009https://doi.org/10.1021/ma902061tCopyright © 2009 American Chemical SocietyRIGHTS & PERMISSIONSArticle Views1537Altmetric-Citations29LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit Read OnlinePDF (907 KB) Get e-AlertsSUBJECTS:Aromatic compounds,Condensation,Diodes,Impurities,Polymers Get e-Alerts