Publications

ADVERTISEMENT RETURN TO ISSUEPREVCommunication to the...Communication to the EditorNEXTNanostructures of n-Type Organic Semiconductor in a p-Type Matrix via Self-Assembly of Block CopolymersStefan M. Lindner and Mukundan ThelakkatView Author Information Makromolekulare Chemie I, Universität Bayreuth, Universitätsstrasse 30, 95440 Bayreuth, Germany Cite this: Macromolecules 2004, 37, 24, 8832–8835Publication Date (Web):October 30, 2004Publication History Received7 September 2004Revised18 October 2004Published online30 October 2004Published inissue 1 November 2004https://pubs.acs.org/doi/10.1021/ma0481656https://doi.org/10.1021/ma0481656rapid-communicationACS PublicationsCopyright © 2004 American Chemical SocietyRequest reuse permissionsArticle Views2697Altmetric-Citations145LEARN 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:Aromatic compounds,Copolymers,Dyes and pigments,Hydrocarbons,Polymers Get e-Alerts

Abstract New classes of liquid‐crystalline semiconductor polymers based on perylene diester benzimidazole and perylene diester imide mesogens are reported. Two highly soluble side‐chain polymers, poly(perylene diester benzimidazole acrylate) (PPDB) and poly(perylene diester imide acrylate) (PPDI) are synthesized by nitroxide‐mediated radical polymerization (NMRP). PPDB shows n‐type semiconductor performance with electron mobilities of 3.2 × 10 −4 cm 2 V −1 s −1 obtained in a diode configuration by fitting the space‐charge‐limited currents (SCLC) according to the Mott–Gurney equation. Interestingly, PPDI performs preferentially as a p‐type material with a hole mobility of 1.5 × 10 −4 cm 2 V −1 s −1 , which is attributed to the less electron‐deficient perylene core of PPDI compared to PPDB. Optical properties are investigated by UV‐vis and fluorescence spectroscopy. The extended π‐conjugation system due to the benzimidazole unit of PPDB leads to a considerably broader absorption in the visible region compared to PPDI. HOMO and LUMO levels of the polymers are also determined by cyclic voltammetry; the resulting energy band‐gaps are 1.86 eV for PPDB and 2.16 eV for PPDI. Thermal behavior and liquid crystallinity are studied by differential scanning calorimetry, polarized optical microscopy, and X‐ray diffraction measurements. The results indicate liquid‐crystalline order of the polymers over a broad temperature range. These thermal, electrical, and optical properties make the perylene side‐chain polymers attractive materials for organic photovoltaics.

Densely surface-grafted monolayer (3-4 nm) poly(3-hexylthiophene) (P3HT) brushes are prepared by click chemistry. For this, P3HT chains with alkyne end groups were synthesized and chemically coupled to a surface-immobilized self-assembled monolayer (SAM) having azide functionality in an organic field-effect transistor channel. The grafted P3HT-alkyne with a molecular weight of M_n,MALDI = 11 400 g mol^-1 ( M_n,SEC = 17 400 g mol^-1) and a narrow distribution of Đ = 1.15, has the highest reported molecular weight for surface-immobilized P3HT brushes. We show the successful grafting of P3HT on the substrate surface with atomic force microscopy, contact angle, and absorption studies. From the film thickness, we can calculate the reduced tethered densities of ∑ = 10.3-12.1, which is indicative of the monolayers being in the true brush regime with high grafting density that is enough to form a compact self-assembled monolayer. The aggregation behavior of the films is characterized by UV-vis spectroscopy and compared to linear P3HT and a bottlebrush copolymer polystyrene- g-P3HT (PS- g-P3HT) with similar P3HT lengths. For such an SAM-based organic field-effect transistor (SAMFET) nanodevice with an ultrathin P3HT layer of 3-4 nm, a very high field-effect mobility of up to 1.8 × 10^-3 cm² V^-1 s^-1 is achieved in channel lengths of 5-20 μm, which is nearly 2 orders of magnitude higher than reported values for polymer-based SAMFETs.

Various fluoro-functionalized aromatic 1,3,5-triazine monomers were prepared. A series low molar mass and poly- (1,3,5-triazine)-ethers were synthesized by a condensation reaction. The polymers as well as the low molar mass compounds have excellent thermal stability and are amorphous. In order to examine the potential to apply these compounds in organic electroluminescent devices, the redox properties were studied by cyclic voltammetry. It was found that the monomers have high electron affinity and reach LUMO values in the range of -2.7 to -3.1 eV. Additionally high oxidation stability with HOMO values lower than -6.4 eV follows hole blocking capabilities. This opens the possibility to utilize 1,3,5-triazine containing materials as electron injection/hole blocking layer in LEDs. First LED results are in agreement to these high electron affinities.

ABSTRACT To obtain novel low‐bandgap materials with tailored hole‐transport properties and extended absorption, electron rich 3,4‐ethylenedioxythiophene is introduced as a comonomer in diketopyrrolo[3,4‐ c ]pyrrole copolymers with different aryl flanking units. The polymers are characterized by absorption and photoluminescence spectroscopy, dynamic scanning calorimetry, cyclic voltammetry, and X‐ray diffraction. The charge transport properties of these new materials are studied carefully using an organic field effect transistor geometry where the charge carriers are transported over a narrow channel at the semiconductor/dielectric interface. These results are compared to bulk charge carrier mobilities using space‐charge limited current (SCLC) measurements, in which the charge carrier is transported through the complete film thickness of several hundred nanometers. Finally, charge carrier mobilities are correlated with the electronic structure of the compounds. We find that in particular the thiophene‐flanked copolymer PDPP[T] 2 ‐EDOT is a very promising candidate for organic photovoltaics, showing an absorption response in the near infrared region with an optical bandgap of 1.15 eV and a very high bulk hole mobility of 2.9 × 10 −4 cm 2 V −1 s −1 as measured by SCLC. This value is two orders of magnitudes higher than SCLC mobilities reported for other polydiketopyrrolopyrroles and is in the range of the well‐known hole transporting polymer poly(3‐hexylthiophene). © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54 , 639–648

ABSTRACT For this study, we have synthesized two different poly(diketopyrrolopyrrole) copolymers with different chain lengths. The diketopyrrolopyrrole (DPP) core is substituted with oligoethylene glycol side chains to increase its compatibility with water and copolymerized with either fluorene or carbazole moieties. The polymers form a composite photocatalyst with anatase TiO 2 . Detailed characterization such as NMR spectroscopy, UV–Vis, DRIFT, and UPS is used to analyze the structural and optical properties as well as the frontier orbital energy levels of the components and the composite materials. The optical properties of the polymers are tunable with respect to the copolymer used, opening up the possibility of optimizing the photocatalytic activity. These composite materials (without the addition of a co‐catalyst) provide up to an eightfold enhancement of the hydrogen evolution reaction (HER) compared to pristine TiO 2 . The polymers also exhibit stability in the reaction medium as shown by solid‐state NMR, DRIFT, and UV–Vis spectroscopy. A significant influence of the chain length of the polymers on HER is found as well. As the chain length increases, the activity toward hydrogen evolution increases. We show a correlation between hydrogen evolution and PDPP chain length whereby the active site of the photocatalytic process remains the inorganic semiconductor.

A combinatorial approach combining vapor deposition of organic molecules and a mask technique was used to prepare on one substrate a matrix of 49 organic light emitting diodes (OLEDs) with different configuration and layer thickness. A landscape library with two orthogonal, linear gradients of an emitter and a hole blocking electron transport material on top of a hole transport layer of constant thickness was prepared. The aim of this experiment was to investigate the influence of an additional electron transport material on the efficiency. Using a semi-automated measurement set-up, the device parameters for each of the 49 OLEDs were evaluated. The existence of an optimum Alq<SUB>3</SUB> layer thickness for two-layer devices ITO/TPD/Alq<SUB>3</SUB>/Al is confirmed and such an optimized two-layer structure could not be improved by adding an additional hole blocking layer to the optimum Alq<SUB>3</SUB> layer. But an improvement of photometric efficiency can be obtained by replacing the optimum Alq<SUB>3</SUB> layer thickness by certain combinations of Alq<SUB>3</SUB>/spiro-Quinoxaline layers.

The use of low molecular weight, oligomeric and polymeric heterocyclics as electron transport/hole-blocking layers in organic light-emitting diodes is reviewed. The most widely applied materials are π-electron deficient heterocyclics carrying imine nitrogen atoms in the aromatic ring, such as 1,3,4-oxadiazoles, 1,2,4-triazoles, 1,3,5-triazines, and 1,4-quinoxalines. Properties such as redox potentials, ionization potential, electron affinity and charge transport mobility of the materials, if known, are taken into consideration to support the electron injection/transport and hole-blocking effectiveness. It can be generalized that heterocyclic moieties with high reduction potential reduce the interface barriers caused by the band offset between organic material and cathode and are most suitable materials for electron injection in organic electroluminescent devices. These materials are generally characterized by high ionization potential values that contribute towards the hole-blocking property. A general comparison of devices and materials is only possible with limitations owing to the variations in device structure, fabrication, electrode materials, emitter materials, etc. © 1998 John Wiley & Sons, Ltd.

All solid-state rechargeable lithium metal batteries (SS-LMBs) are gaining more and more importance because of their higher safety and higher energy densities in comparison to their liquid-based counterparts. In spite of this potential, their low discharge capacities and poor rate performances limit them to be used as state-of-the-art SS-LMBs. This arise due to the low intrinsic ionic and electronic transport pathways within the solid components in the cathode during the fast charge/discharge processes. Therefore, it is necessary to have a cathode with good electron conducting channels to increase the active material utilization without blocking the movement of lithium ions. Since SS-LMBs require a different morphology and composition of the cathode, we selected LiFePO₄ (LFP) as a prototype and, we have systematically studied the influence of the cathode composition by varying the contents of active material LFP, conductive additives (super C65 conductive carbon black and conductive graphite), ion conducting components (PEO and LiTFSI) in order to elucidate the best ion as well as electron conduction morphology in the cathode. In addition, a comparative study on different cathode slurry preparation methods was made, wherein ball milling was found to reduce the particle size and increase the homogeneity of LFP which further aids fast Li ion transport throughout the electrode. The SEM analysis of the resulting calendered electrode shows the formation of non-porous and crack-free structures with the presence of conductive graphite throughout the electrode. As a result, the optimum LFP cathode composition with solid polymer nanocomposite electrolyte (SPNE) delivered higher initial discharge capacities of 114 mAh g^-1 at 0.2C rate at 30 °C and 141 mAh g^-1 at 1C rate at 70 °C. When the current rate was increased to 2C, the electrode still delivered high discharge capacity of 82 mAh g^-1 even after 500 cycle, which indicates that the optimum cathode formulation is one of the important parameters in building high rate and long cycle performing SS-LMBs.