Platani, Greece
Platani, Greece

Time filter

Source Type

Chochos C.L.,University of Ioannina | Singh R.,Pohang University of Science and Technology | Kim M.,Pohang University of Science and Technology | Gasparini N.,Friedrich - Alexander - University, Erlangen - Nuremberg | And 10 more authors.
Advanced Functional Materials | Year: 2016

Optoelectronic properties, supramolecular assemblies, and morphology variation of polymeric semiconductors are governed by six fundamental chemical features. These features are molecular weight, bond length alternation (BLA), planarity, aromatic resonance energy, substituents, and intermolecular interactions. Of these features the specific role of BLA in determining the performance of a polymeric semiconductor in practical technological applications is so far unknown. This study investigates this question and reports the novel finding that the optoelectronic, microscopic (supramolecular packing), and macroscopic (morphology variation and device performance) properties of model semiconducting polymers depend on the conjugated polymer backbone enlargement, which is directly related to the BLA. Extensive studies are performed in both single-component polymer films and their blends with fullerene derivatives. Understanding the specific structure-properties relations will lead to significant advancement in the area of organic electronics, since it will set new design rules toward further optimization of polymer chemical structures to enhance the device performances. An efficient way to enlarge the polymer backbone of an electron donor conjugated polymer toward higher organic photovoltaic performance is presented. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA.

Singh R.,Italian Institute of Technology | Pagona G.,Advent Technologies SA | Pagona G.,National Hellenic Research Foundation | Gregoriou V.G.,Advent Technologies SA | And 12 more authors.
Polymer Chemistry | Year: 2015

The influence of the monomer's isomeric structure on the optical, electrochemical, charge transporting properties and photovoltaic performance of donor-acceptor (D-A) conjugated polymers has been demonstrated for the first time by studying two D-A copolymers consisting of bis(3-octyloxy)phenyl)quinoxaline as the electron deficient unit and the two isomeric structures of thienothiophene (thieno[3,2-b]thiophene and thieno[2,3-b]thiophene) as the electron rich units. The drastic effect of incorporating two different isomeric structures on the polymer backbone of these copolymers, manifests in changes observed in their optical, electrochemical and charge transporting properties. In contrast, the overall photovoltaic performance of the copolymers is similar, but distinct differences in the device photocurrents occur. These differences were attributed to morphology variations rather than the balanced mobility ratio. For further developments in the field, the isomeric structures of different functional monomers should be considered in the designing of new materials with even superior performance. © 2015 The Royal Society of Chemistry.

Kakogianni S.,University of Patras | Lebedeva M.A.,University of Oxford | Paloumbis G.,Advent Technologies SA | Andreopoulou A.K.,University of Patras | And 4 more authors.
RSC Advances | Year: 2016

An efficient route to synthesise hybrid polymers consisting of a semiconducting polymer and a fullerene unit, for BHJ OPV devices is presented herein. The synthetic procedure is based on the in situ functionalisation of regioregular polythiophenes of various molecular weights with perfluorophenyl moieties at the ω end position of the polymeric chains, after the GRIM polymerisation reaction. Each of the perfluorophenyl moieties is then decorated with an azide group, and employed in a [3 + 2] cycloaddition reaction with fullerene species, i.e. C70 or IC70MA, yielding P3HT-fullerene hybrids covalently linked via aziridine bridges. The effectiveness of the purification procedures of the above organic and hybrid materials were evaluated by extended spectroscopic and chromatographic methods. The optical and electrochemical characterisation of the resulting hybrid structures revealed that the unique optoelectronic properties of the P3HT polymers are retained in the hybrid materials. Whereas the morphological properties are largely affected by the introduction of the C70 and IC70MA fullerenes. The enhanced and tunable nanophase separation observed in the polymer-fullerene hybrid films coupled with their excellent optoelectronic properties makes them exciting potential polymeric additives for the P3HT:IC70BA active blends. © 2016 Royal Society of Chemistry.

Papadimitriou K.D.,University of Patras | Paloukis F.,Advent Technologies S.A. | Neophytides S.G.,Foundation for Research and Technology Hellas | Kallitsis J.K.,University of Patras | Kallitsis J.K.,Foundation for Research and Technology Hellas
Macromolecules | Year: 2011

Novel aromatic polyethers bearing polar pyridine units along the main chain and side cross-linkable propenyl groups have been successfully synthesized. Their properties relating to their ability to be used as polymer electrolyte membranes for high temperature fuel cell applications, were thoroughly investigated. Cross-linked membranes were obtained by thermal curing of the cross-linkable polymers with the use of a bisazide as the cross-linking agent. The glass transition temperatures of the cross-linked membranes were determined by dynamic mechanical analysis and found to be higher compared to the neat polymers proving the successful cross-linked network. The doping ability in phosphoric acid and the proton conductivity of the cross-linked membranes were higher compared to the noncross-linked analogues. Finally, membrane electrode assemblies (MEAs) were constructed and tested in a single cell at temperatures between 180 and 220 °C. The superior performance of the cross-linked membranes in combination with the operating stability at 200 °C for 48 h demonstrate the potential use of these materials as electrolytes for high temperature PEM fuel cells. © 2011 American Chemical Society.

Geormezi M.,University of Patras | Chochos C.L.,Advent Technologies SA | Gourdoupi N.,Advent Technologies SA | Neophytides S.G.,Advent Technologies SA | And 3 more authors.
Journal of Power Sources | Year: 2011

Novel aromatic polyether type copolymers bearing side chain polar pyridine rings as well as combination of main and side chain pyridine units have been evaluated as potential polymer electrolytes for proton exchange membrane fuel cells (PEMFCs). The advanced chemical and physicochemical properties of these new polymers with their high oxidative stability, mechanical integrity and high glass transition temperatures (Tg's up to 270 °C) and decomposition temperatures (Td's up to 480 °C) make them promising candidates for high and medium temperature proton exchange membranes in fuel cells. These copolymers exhibit adequate proton conductivities up to 0.08 S cm-1 even at moderate phosphoric acid doping levels. An optimized terpolymer chemical structure has been developed, which has been effectively tested as high temperature phosphoric acid imbibed polymer electrolyte. MEA prepared out of the novel terpolymer chemical structure is approaching state of the art fuel cell operating performance (135 mW cm -2 with electrical efficiency 45%) at high temperatures (150-180 °C) despite the low phosphoric acid content (<200 wt%) and the low platinum loading (ca. 0.7 mg cm-2). Durability tests were performed affording stable performance for more than 1000 h. © 2011 Elsevier B.V.

Papadimitriou K.D.,University of Patras | Papadimitriou K.D.,Institute of Chemical Engineering science FORTH ICE HT | Geormezi M.,Advent Technologies S.A. | Neophytides S.G.,Institute of Chemical Engineering science FORTH ICE HT | And 2 more authors.
Journal of Membrane Science | Year: 2013

Cross-linkable aromatic polyethers combining main and side chain pyridine units as well as side double bonds were successfully synthesized and characterized. Aiming at the use of these materials as electrolytes at high temperature fuel cells, these polymers were subjected to covalent cross-linking in order to improve their mechanical properties and their stability in the doped state. The cross-linking was obtained via cationic polymerization of the double bonds, during the impregnation of the produced membranes in phosphoric acid. The cross-linking was confirmed by the increased glass transition temperatures, the improved thermal stability and the insolubility of the cross-linked membranes compared to their undoped non cross-linked counterparts. Selected cross-linked membranes were used for membrane electrode assembly (MEA) preparation and tested in a single cell at temperatures between 180 and 220°C. Long-term durability tests were also performed at 180°C and at a current density of 0.2A/cm2. The experiment showed a stable operation without degradation for 1000h. The promising performance and the durability of the tested materials in combination with the simple and convenient technique which used to produce cross-linked membranes, demonstrates the feasibility of this type of electrolytes to be used in high temperature PEM fuel cell applications. © 2013 Elsevier B.V.

Geormezi M.,Advent Technologies S.A. | Deimede V.,Advent Technologies S.A. | Deimede V.,University of Patras | Kallitsis J.K.,Advent Technologies S.A. | And 4 more authors.
Journal of Membrane Science | Year: 2012

New blend systems consisting of copolymers based on aromatic polyethers bearing both main and side chain pyridine units have been prepared in order to be evaluated as proton exchange membranes. The blend membranes showed high glass transition temperatures up to 265°C and high thermal (T d's up to 450°C) as well as oxidative stability. The acid doping ability was controlled based on the blend constituents and composition while the maximum doping levels were up to 480wt%. Comparison of different blend membranes with the same doping level showed that different conductivity values were obtained (up to 1.1×10 -1Scm -1), denoting the important role of the polymer matrix itself on proton conduction. Morphological investigation by means of SEM revealed nanophase separated structures with spherical clusters of average sizes between 50 and 70nm. MEAs based on the newly developed blends were prepared and preliminary fuel cell tests at temperatures up to 180°C using dry gases were conducted. The performance obtained was satisfactory (723mV at 0.2Acm -2 at 180°C using H 2/O 2 gases) and close to the state of the art PBI MEAs. © 2012 Elsevier B.V.

Yau C.P.,Imperial College London | Fei Z.,Imperial College London | Ashraf R.S.,Imperial College London | Shahid M.,Imperial College London | And 6 more authors.
Advanced Functional Materials | Year: 2014

A series of donor-acceptor (D-A) conjugated polymers utilizing 4,4-bis(2-ethylhexyl)-4H-germolo[3,2-b:4,5-b′]dithiophene (DTG) as the electron rich unit and three electron withdrawing units of varying strength, namely 2-octyl-2H-benzo[d][1,2,3]triazole (BTz), 5,6-difluorobenzo[c][1,2,5] thiadiazole (DFBT) and [1,2,5]thiadiazolo[3,4-c]pyridine (PT) are reported. It is demonstrated how the choice of the acceptor unit (BTz, DFBT, PT) influences the relative positions of the energy levels, the intramolecular transition energy (ICT), the optical band gap (Egopt), and the structural conformation of the DTG-based co-polymers. Moreover, the photovoltaic performance of poly[(4,4-bis(2-ethylhexyl)-4H-germolo[3,2-b:4,5-b′] dithiophen-2-yl)-([1,2,5]thiadiazolo[3,4-c]pyridine)] (PDTG-PT), poly[(4,4-bis(2-ethylhexyl)-4H-germolo[3,2-b:4,5-b′]dithiophen-2-yl) -(2-octyl-2H-benzo[d][1,2,3]triazole)] (PDTG-BTz), and poly[(4,4-bis(2- ethylhexyl)-4H-germolo[3,2-b:4,5-b′]dithiophen-2-yl)-(5,6-difluorobenzo[c] [1,2,5]thiadiazole)] (PDTG-DFBT) is studied in blends with [6,6]-phenyl-C 70-butyric acid methyl ester (PC70BM). The highest power conversion efficiency (PCE) is obtained by PDTG-PT (5.2%) in normal architecture. The PCE of PDTG-PT is further improved to 6.6% when the device architecture is modified from normal to inverted. Therefore, PDTG-PT is an ideal candidate for application in tandem solar cells configuration due to its high efficiency at very low band gaps (Egopt = 1.32 eV). Finally, the 6.6% PCE is the highest reported for all the co-polymers containing bridged bithiophenes with 5-member fused rings in the central core and possessing an Egopt below 1.4 eV. The optoelectronic properties and photovoltaic device performance for a series of low band gap donor-acceptor polymers based upon dithienogermole are reported. One very low band gap polymer, PDTG-PT, (Egopt = 1.32 eV) is shown to exhibit a promising device efficiency of 6.6% when utilized in inverted photovoltaic devices, making it a promising candidate for incorporation in tandem solar cell devices. © 2013 The Authors. Advanced Functional Materials published by Wiley-VCH Verlag GmbH 8 Co. KGaA Weinheim.

Chochos C.L.,Advent Technologies SA | Chochos C.L.,Foundation for Research and Technology Hellas | Tagmatarchis N.,National Hellenic Research Foundation | Gregoriou V.G.,Advent Technologies SA | Gregoriou V.G.,Foundation for Research and Technology Hellas
RSC Advances | Year: 2013

The demand for further optimization of the photovoltaic efficiency has stimulated an intensive research effort both for new low-band-gap polymeric materials as electron donors and for new efficient electron-accepting materials. As regards the latter, less attention has been observed on the optimization of the electron acceptor material compared to the extensive studies on the electron donor polymer in organic photovoltaic (OPV) cells. The majority of the acceptor materials used so far in solar cells are organic (carbon based) materials, however other traditional acceptor materials include inorganic semiconductors, such as cadmium selenide (CdSe) nanocrystals, titanium oxide (TiO2) and zinc oxide (ZnO) nanoparticles. From the implemented organic materials high power conversion efficiencies PCEs (>9.0%) are observed in OPVs utilizing fullerene derivatives and especially [6,6]-phenyl-C61 butyric acid methyl ester (PC60BM) as the acceptor. Recently, very promising efficiencies of ∼5.0% have been also obtained by Polyera corporation utilizing soluble conjugated polymers as both the donor and the acceptor components. It is therefore expected that through improved materials design for enhancing the electron mobility, better tuning of the energy levels and absorption profile of organic materials, significant improvements in the device performance can still be expected. In this work, the current trends on the most promising solution processable n-type organic materials (fullerene derivatives, small molecules and conjugated polymers) will be presented in detail, emphasizing on the correlation between structure/optoelectronic properties/morphology characterization and device performances. © The Royal Society of Chemistry 2013.

Geormezi M.,ADVENT Technologies S.A. | Paloukis F.,ADVENT Technologies S.A. | Orfanidi A.,Foundation for Research and Technology Hellas | Shroti N.,Foundation for Research and Technology Hellas | And 2 more authors.
Journal of Power Sources | Year: 2015

Abstract The effect of reformate H2 mixture composition on Pt/C based high temperature PEMFC anode was thoroughly studied, in order to understand the anode's tolerance under varying CO and steam partial pressures. It is shown that under steam partial pressure over 12 kPa a high overpotential region appears at current densities over 0.3 A/cm2. This negative effect appears in relation to the structure of the electrochemical interface (EI), as this is specified by the amount of H3PO4 (PA) within the anode catalytic layer. As also shown, the sustainable operation of the anode under reformate containing steam and CO as high as 30 kPa and 2 kPa respectively requires significantly lower loadings of PA. This malfunctioning is attributed to the hydrophobic/hydrophilic properties of the Pt/C-PA EI and its modification when water from the gas phase is dissolved in the PA, in combination with the polarization and the adsorption of CO and H2 on Pt surface. These phenomena and the capillary forces within the catalytic layer are responsible for the alternating contraction (ganglia formation and loss of ionic link within the EI) and spreading (thin film formation and well developed EI) of PA, thus giving rise to oscillatory behavior and unstable performance of the anode. © 2015 Elsevier B.V. All rights reserved.

Loading Advent Technologies SA collaborators
Loading Advent Technologies SA collaborators