Suchergebnisse

Silver nanowire networks have demonstrated significant potential as semi-transparent electrodes for various applications. However, for their widespread utilisation in devices, upscaled coating technologies such as screen-printing need to be explored and related to this, the formulation of suitable inks is indispensable. This work contributes to this effort by the synthesis of Ag-NW based formulations. The rheological characteristics that are essential for screen-printing are obtained by the addition of hydrophobically modified cellulose. The electrical and optical characteristics of screen-printed features on PET are compared by a Van der Pauw method and UV–vis spectroscopy. Despite the presence of the cellulose additive, the screen-printed electrodes exhibit a transmittance from 92.8% to 57.3% and a sheet resistance down to 27 Ohm sq−1. Based on the percolation theory in composites, a mathematical expression is presented, which allows the in-depth analysis of the resulting opto-electrical properties. The application potential of the nanowire-containing formulations is finally demonstrated by screen-printing functional, flexible electroluminescent devices. ; This project has received funding from the European Union's Horizon 2020 research and innovation programme under grant agreement No 641864.

In this work, the synthesis of N,N'-dialkyl-6,6'-dibromoisoindigo derivatives by continuous-flow chemistry is explored as a means to enhance material availability and structural diversity, in particular toward the application of isoindigo-based semiconductors in high-performance organic photovoltaic devices. The individual steps in the conventional batch synthesis protocol are evaluated and, when needed, adapted to flow reactors. To overcome the low solubility of non-alkylated 6,6'-dibromoisoindigo in common organic solvents, the flow condensation reaction between the 6-bromo-isatin and 6-bromo-oxindole precursors is evaluated in polar aprotic solvents. Dialkylation of 6,6'-dibromoisoindigo is readily performed in flow using a solid-phase reactor packed with potassium carbonate. In an alternative strategy, solubility is ensured by first introducing the N-alkyl side chains on 6-bromo-isatin and 6-bromo-oxindole (accessible via a high-yielding flow reduction of alkylated 6-bromo-isatin), followed by condensation using the conventional method in acetic-hydrochloric acid medium. The N, N'-dialkylated 6,6'-dibromoisoindigo derivatives indeed show enhanced solubility in the hot reaction mixture compared to the non-alkylated material but eventually precipitate when the reaction mixture is cooled down. Nevertheless, the condensation between both alkylated starting materials is achieved in flow without any blockages by keeping the outlet from the reactor heated and as short as possible. The latter strategy allows the preparation of both symmetrically and asymmetrically N-substituted isoindigo compounds. ; This work was supported by the project ORGANEXT (EMR INT4-1.2-2009-04/054), selected in the frame of the operational program INTERREG IV-A Euregio Maas-Rijn, and the IAP 7/05 project FS2 (Functional Supramolecular Systems), granted by the Science Policy Office of the Belgian Federal Government (BELSPO). We are also grateful for financial support by the Research Program of the Research Foundation - Flanders (FWO) (project G.0415.14 N and M. ERA-NET project RADESOL). G. Pirotte thanks Hasselt University for his PhD scholarship. J. Brebels and P. Verstappen acknowledge the Agency for Innovation by Science and Technology in Flanders (IWT) for their PhD grants. We further acknowledge Hercules for providing the funding for the LTQ Orbitrap Velos Pro mass spectrometer. Hasselt University and IMO-IMOMEC are partners within the Solliance network, the strategic alliance for research and development in the field of thin-film PV energy in the Eindhoven-Leuven-Aachen region.

Metal nanowire networks are a promising concept for replacing ITO in transparent electrodes for a range of optoelectronic devices. In these networks, the nanowires conduct charge carriers, while the open areas allow the transmission of light. Metal nanowires are both printable and achieve a performance equivalent to ITO upon thermal processing at temperatures below 150°C which make them ideal for depositing transparent electrodes on plastic substrates. For this contribution, silver nanowires (AgNWs) were synthesized using a polyol synthesis method. Various formulations containing AgNWs were prepared and their rheological behavior was assessed in view of screen printing. The most promising formulations were selected to print test features on PET substrates and the electrical and optical characteristics of these features were measured by a Van der Pauw method and UV-Vis spectroscopy respectively. By the addition of AgNWs to a PEDOT-based formulation, the sheet resistance of the printed features can be decreased from ca. 200 Ohm/sq to values below 40 Ohm/sq, indicating that a nanowire network improves the conductivity. However these features appear blue due to the absorption of (infra-)red light by PEDOT. The optical properties can be significantly enhanced by replacing the PEDOT-based formulation by a cellulose-based formulation. ; This project has received funding from the European Union's Horizon 2020 research and innovation programme under grant agreement No 641864.

Although controlled polymerization procedures for conjugated polymers have considerable advantages with respect to molar mass and end group control, the material scope has been very limited, in particular considering block copolymers and donor–acceptor type all-conjugated polymers, imposing considerable challenges upon the synthetic polymer community. In this work, a push–pull monomer consisting of a thiophene (donor) and a pyridine (acceptor) unit is synthesized and subsequently polymerized via Kumada catalyst-transfer polymerization using a nickel catalyst (GRIM polymerization). In this way, an alternating donor–acceptor copolymer is obtained via a chain-growth mechanism. Furthermore, an all-conjugated block copolymer containing a poly(3-hexylthiophene) block and the alternating copolymer is successfully prepared in a one-pot procedure as well. The diblock structure is confirmed by comparison of the thermal, electrochemical, and spectroscopic properties of the block copolymer and its constituting polymer parts. ; This work was supported by the IAP 7/05 project "Functional Supramolecular Systems", granted by the Science Policy Office of the Belgian Federal Government (BELSPO). We are also grateful for financial support by the Research Program of the Research Foundation−Flanders (FWO) (project G.0415.14N). S.G. acknowledges Hasselt University for her (BOF) doctoral grant. TA Instruments is acknowledged for the RHC equipment.

A kinetic Monte Carlo modeling study is presented for precursor polymer formation via the sulfinyl precursor route. The premonomer, 1-(chloromethyl)-4-[(n-octylsulfinyl)methyl]benzene, is subjected to a NatBuO induced 1,6-elimination in sBuOH yielding the actual p-quinodimethane monomer that leads, via a radical polymerization, to the precursor polymer. The kinetic Monte Carlo model is able to predict the experimental trends in yield, mass averaged molar mass and structural defect content. The effect of radical recombination and cyclization is modeled and found to be negligible. The effect of the initial base and premonomer concentration on the polymer properties is investigated. Simulation results indicate a maximum in the polymer yield and chain length for initial [base]/[premonomer] = 1 and that the molecular properties of the precursor polymers can be varied by as much as 50% by an appropriate choice of initial [base]/[premonomer]. The kinetic Monte Carlo model is used to determine reaction conditions to achieve targeted polymer yields, chain lengths and structural defect contents. ; P.V.S. acknowledges financial support from the Interuniversity Attraction Poles Programme, Belgian State, Belgian Science Policy, the Institute for the Promotion of Innovation through Science and Technology in Flanders (IWT Vlaanderen), and the "Long Term Structural Methusalem Funding by the Flemish Government". J.V. gratefully acknowledges the fund for Scientific Research Flanders (FWO), for granting a Ph.D. fellowship.

Continuous flow chemistry has been shown to be a suitable method for the large-scale preparation of conjugated polymers with uniform structural and macromolecular characteristics, which is especially relevant when applying these materials in optoelectronic devices. The molecular weight and dispersity of conjugated polymers have a major effect on final device performance through a combination of processing and morphological considerations. In this work, the low bandgap polymer PffBT4T-2OD ('PCE-11'), which provides highly efficient bulk heterojunction solar cells, is synthesized by continuous flow chemistry using an easily mountable home-made apparatus. The influence of various reaction parameters on the material characteristics is investigated. Particular attention is devoted to tuning of the molecular weight, as this has a major impact on solubility and processability of the resultant polymer and, ultimately, solar cell performance. We find that temperature, monomer concentration, and injection volume of the polymerization mixture are significant parameters that can be used to optimize the control over molecular weight. The same protocol is then also applied to a structurally similar polymer with longer alkyl side chains, PffBT4T-2DT, affording important advantages in terms of processing due to its higher solubility. An average power conversion efficiency of 9.4% for bulk heterojunction solar cells using PC71BM as the acceptor phase is achieved based on this flow-synthesized polymer. ; The authors of the Georgia Institute of Technology thank the National Science Foundation for support through the CCI Center for Selective C-H Functionalization (CHE-1205646) and the Department of the Navy, Office of Naval Research for support through Award No. N00014-14-1-0580 (CAOP MURI). The Belgian co-authors thank Hasselt University for continuing financial support. This work is also supported by the IAP 7/05 project Functional Supramolecular Systems, granted by the Science Policy Office of the Belgian Federal Government (BEL-SPO). We are also grateful for financial support by the Research Foundation - Flanders (FWO) (projects G.0415.14N and G.0B67.15N). Most of the work was performed during the stay of G. Pirotte as a visiting researcher at Georgia Institute of Technology, funded by the FWO (V4.298.16N) and a personal grant from the District 1630 of Rotary International, supported by the Rotary Foundation.

Three extended molecular chromophores, differing in their central acceptor moiety and specifically designed as electron donor components for small molecule organic solar cells, are synthesized via a two-fold-C-H arylation protocol. Upon removal of the side products inherent to the applied direct (hetero) arylation procedure, a record power conversion efficiency of 5.1% is achieved. ; We acknowledge financial support from the Science Policy Office of the Belgian Federal Government (BELSPO; IAP 7/05 project FS2), the Agency for Innovation by Science and Technology in Flanders (IWT; PhD grants J. Brebels and T. Vangerven) and the Research Programme of the Research Foundation - Flanders (FWO; M.ERA-NET project RADESOL and projects G.0415.14N/G.0B67.15N).

Conjugated polyelectrolyte (CPE) interfacial layers present a powerful way to boost the I-V characteristics of organic photovoltaics. Nevertheless, clear guidelines with respect to the structure of high-performance interlayers are still lacking. In this work, impedance spectroscopy is applied to probe the dielectric permittivity of a series of polythiophene-based CPEs. The presence of ionic pendant groups grants the formation of a capacitive double layer, boosting the charge extraction and device efficiency. A counteracting effect is the diminishing affinity with the underlying photoactive layer. To balance these two effects, we found copolymer structures containing nonionic side chains to be beneficial. ; Funding Agencies|IAP project Functional Supramolecular Systems [7/05]; Science Policy Office of the Belgian Federal Government (BELSPO); Research Program of the Research Foundation Flanders (FWO) [G.0415.14N]; Foundation for Fundamental Research on Matter (FOM) from The Netherlands Organization for Scientific Research (NWO) [V0714M-13MV60]; Swedish Research Council Linnaeus LiLi-NFM at Linkoping University; Vrije Universiteit Brussel (VUB); University of Montpellier; CNRS; University of Mons

This work is part of the inter-laboratory collaboration to study the stability of seven distinct sets of state-of-the-art organic photovoltaic (OPV) devices prepared by leading research laboratories. All devices have been shipped to and degraded at RISempty set-DTU up to 1830 hours in accordance with established ISOS-3 protocols under defined illumination conditions. In this work, we apply the Incident Photon-to-Electron Conversion Efficiency (IPCE) and the in situ IPCE techniques to determine the relation between solar cell performance and solar cell stability. Different ageing conditions were considered: accelerated full sun simulation, low level indoor fluorescent lighting and dark storage. The devices were also monitored under conditions of ambient and inert (N-2) atmospheres, which allows for the identification of the solar cell materials more susceptible to degradation by ambient air (oxygen and moisture). The different OPVs configurations permitted the study of the intrinsic stability of the devices depending on: two different ITO-replacement alternatives, two different hole extraction layers (PEDOT:PSS and MoO3), and two different P3HT-based polymers. The response of un-encapsulated devices to ambient atmosphere offered insight into the importance of moisture in solar cell performance. Our results demonstrate that the IPCE and the in situ IPCE techniques are valuable analytical methods to understand device degradation and solar cell lifetime. ; This work has been supported by the Danish Strategic Research Council (2104-07-0022), EUDP (j.no. 64009-0050), and the Danish National Research Foundation. Partial financial support was also received from the European Commission as part of the Framework 7 ICT 2009 collaborative project HIFLEX (grant no. 248678), partial financial support from the EUIndian framework of the "Largecells" project that received funding from the European Commission's Seventh Framework Programme (FP7/2007-2013. grant no. 261936), partial financial support was also received from the European Commission as part of the Framework 7 ICT 2009 collaborative project ROTROT (grant no. 288565) and from PVERA-NET (project acronym POLYSTAR). To CONACYT (Mexico) for the Ph.D. scholarship awarded to G. T.-E, to the Spanish Ministry of Science and Innovation, MICINN-FEDER project ENE2008-04373, to the Consolider NANOSELECT project CSD2007-00041, to the Xarxa de Referencia en Materials Avancats per a l'Energia, XaRMAE of the Catalonia Government (Spain). RR and HH are grateful for financial support from the Thuringian Ministry of Culture and the German Federal Ministry of Education and Research in the frameworks of FIPV II and PPP (contract number 13N9843), respectively. DMT acknowledges generous support from the Inger and Jens Bruun Foundation through The American-Scandinavian Foundation.

The present work is the fourth (and final) contribution to an inter-laboratory collaboration that was planned at the 3rd International Summit on Organic Photovoltaic Stability (ISOS-3). The collaboration involved six laboratories capable of producing seven distinct sets of OPV devices that were degraded under well-defined conditions in accordance with the ISOS-3 protocols. The degradation experiments lasted up to 1830 hours and involved more than 300 cells on more than 100 devices. The devices were analyzed and characterized at different points of their lifetimes by a large number of non-destructive and destructive techniques in order to identify specific degradation mechanisms responsible for the deterioration of the photovoltaic response. Work presented herein involves time-of-flight secondary ion mass spectrometry (TOF-SIMS) in order to study chemical degradation in-plane as well as in-depth in the organic solar cells. Various degradation mechanisms were investigated and correlated with cell performance. For example, photo-oxidation of the active material was quantitatively studied as a function of cell performance. The large variety of cell architectures used (some with and some without encapsulation) enabled valuable comparisons and important conclusions to be drawn on degradation behaviour. This comprehensive investigation of OPV stability has significantly advanced the understanding of degradation behaviour in OPV devices, which is an important step towards large scale application of organic solar cells. ; This work has been supported by the Danish Strategic Research Council (2104-07-0022), EUDP (j.no. 64009-0050, 64009-0051) and the Danish National Research Foundation. Partial financial support was also received from the European Commission as part of the Framework 7 ICT 2009 collaborative project HIFLEX (grant no. 248678), partial financial support from the EUIndian framework of the "Largecells'' project that received funding from the European Commission's Seventh Framework Programme (FP7/2007-2013. grant no. 261936), partial financial support was also received from the European Commission as part of the Framework 7 ICT 2009 collaborative project ROTROT (grant no. 288565) and from PVERA-NET (project acronym POLYSTAR). are due to CONACYT (Mexico) for the PhD scholarship awarded to G. T.-E; to the Spanish Ministry of Science and Innovation, MICINN-FEDER project ENE2008-04373; to the Consolider NANOSELECT project CSD2007-00041; to the Xarxa de Referencia en Materials Avancats per a l'Energia, XaRMAE of the Catalonia Government (Spain). RR and HH are grateful for financial support from the Thuringian Ministry of Culture and the German Federal Ministry of Education and Research in the frameworks of FIPV II and PPP (contract number 13N9843), respectively. DMT acknowledges generous support from the Inger and Jens Bruun Foundation through The American-Scandinavian Foundation.