Jurgen Kesters
University of Hasselt
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Publication
Featured researches published by Jurgen Kesters.
Journal of Photonics for Energy | 2014
Ilaria Cardinaletti; Jurgen Kesters; Sabine Bertho; Bert Conings; Fortunato Piersimoni; J. D’Haen; Laurence Lutsen; Milos Nesladek; Bruno Van Mele; Guy Van Assche; Koen Vandewal; Alberto Salleo; Dirk Vanderzande; Wouter Maes; Jean Manca
Abstract. When state-of-the-art bulk heterojunction organic solar cells with ideal morphology are exposed to prolonged storage or operation at elevated temperatures, a thermally induced disruption of the active layer blend can occur, in the form of a separation of donor and acceptor domains, leading to diminished photovoltaic performance. Toward the long-term use of organic solar cells in real-life conditions, an important challenge is, therefore, the development of devices with a thermally stable active layer morphology. Several routes are being explored, ranging from the use of high glass transition temperature, cross-linkable and/or side-chain functionalized donor and acceptor materials, to light-induced dimerization of the fullerene acceptor. A better fundamental understanding of the nature and underlying mechanisms of the phase separation and stabilization effects has been obtained through a variety of analytical, thermal analysis, and electro-optical techniques. Accelerated aging systems have been used to study the degradation kinetics of bulk heterojunction solar cells in situ at various temperatures to obtain aging models predicting solar cell lifetime. The following contribution gives an overview of the current insights regarding the intrinsic thermally induced aging effects and the proposed solutions, illustrated by examples of our own research groups.
Chemsuschem | 2015
Geert Pirotte; Jurgen Kesters; Pieter Verstappen; Sanne Govaerts; Jean Manca; Laurence Lutsen; Dirk Vanderzande; Wouter Maes
Organic photovoltaics (OPV) have attracted great interest as a solar cell technology with appealing mechanical, aesthetical, and economies-of-scale features. To drive OPV toward economic viability, low-cost, large-scale module production has to be realized in combination with increased top-quality material availability and minimal batch-to-batch variation. To this extent, continuous flow chemistry can serve as a powerful tool. In this contribution, a flow protocol is optimized for the high performance benzodithiophene-thienopyrroledione copolymer PBDTTPD and the material quality is probed through systematic solar-cell evaluation. A stepwise approach is adopted to turn the batch process into a reproducible and scalable continuous flow procedure. Solar cell devices fabricated using the obtained polymer batches deliver an average power conversion efficiency of 7.2 %. Upon incorporation of an ionic polythiophene-based cathodic interlayer, the photovoltaic performance could be enhanced to a maximum efficiency of 9.1 %.
Journal of Materials Chemistry | 2014
Wouter Vanormelingen; Jurgen Kesters; Pieter Verstappen; Jeroen Drijkoningen; Julija Kudrjasova; Simplice Koudjina; Vincent Liégeois; Benoît Champagne; Jean Manca; Laurence Lutsen; Dirk Vanderzande; Wouter Maes
A series of low bandgap copolymers composed of N-acyl-substituted dithieno[3,2-b:2′,3′-d]pyrroles (DTPs) as the electron rich donor constituents (with various alkyl side chain patterns) combined with different electron deficient acceptor building blocks are developed for polymer solar cell applications. Due to the introduction of the N-acyl substituents, the HOMO energy levels of the push–pull copolymers decrease as compared to the N-alkyl-DTP analogues, resulting in an increased open-circuit voltage (Voc) and hence solar cell performance. For an N-acyl-DTP-alt-thieno[3,4-c]pyrrole-4,6-dione (PDTP-TPD) copolymer a bulk heterojunction device with a Voc up to 0.80 V and a power conversion efficiency of 4.0% is obtained, the highest value for DTP-based polymer materials to date. Moreover, by implementation of a conjugated polyelectrolyte cathode interlayer the short-circuit current noticeably increases, enhancing the solar cell efficiency to 5.8%.
Journal of Materials Chemistry | 2015
Pieter Verstappen; Jurgen Kesters; Wouter Vanormelingen; Gaël H. L. Heintges; Jeroen Drijkoningen; Tim Vangerven; Lidia Marin; Simplice Koudjina; Benoît Champagne; Jean Manca; Laurence Lutsen; Dirk Vanderzande; Wouter Maes
The effect of fluorination on the optoelectronic properties and the polymer : fullerene solar cell characteristics of PCPDTQx-type (poly{4-(2′-ethylhexyl)-4-octyl-4H-cyclopenta[2,1-b:3,4-b′]dithiophene-alt-2,3-bis[5′-(2′′-ethylhexyl)thiophen-2′-yl]quinoxaline}) low bandgap copolymers is reported. The introduction of fluorine atoms on the quinoxaline constituents is an effective way to lower the HOMO and LUMO energy levels of the alternating copolymers, resulting in an enhanced open-circuit voltage for the devices based on the fluorinated polymers (∼0.1 V per F added). Furthermore, fluorination also improves the charge carrier mobility in the bulk heterojunction blends. Despite the formation of unfavorable photoactive layer morphologies, the best solar cell performance is obtained for the copolymer prepared from the difluorinated quinoxaline monomer, affording a power conversion efficiency of 5.26% under AM 1.5G irradiation, with an open-circuit voltage of 0.83 V, a short-circuit current density of 11.58 mA cm−2 and a fill factor of 55%.
ACS Applied Materials & Interfaces | 2016
Jurgen Kesters; Sanne Govaerts; Geert Pirotte; Jeroen Drijkoningen; Michèle Chevrier; Niko Van den Brande; Xianjie Liu; Mats Fahlman; Bruno Van Mele; Laurence Lutsen; Dirk Vanderzande; Jean Manca; Sébastien Clément; Elizabeth von Hauff; Wouter Maes
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.
Journal of Materials Chemistry | 2016
Julija Kudrjasova; Jurgen Kesters; Pieter Verstappen; Jeroen Brebels; Tim Vangerven; Ilaria Cardinaletti; Jeroen Drijkoningen; Huguette Penxten; Jean Manca; Laurence Lutsen; Dirk Vanderzande; Wouter Maes
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.
RSC Advances | 2015
Wouter Marchal; Christopher De Dobbelaere; Jurgen Kesters; Gilles Bonneux; Joke Vandenbergh; Hanne Damm; Thomas Junkers; Wouter Maes; Jan D'Haen; Marlies K. Van Bael; An Hardy
A systematic study of a combustion precursors thermal decomposition pathway is undertaken, in both powders and thin films, to obtain insights in the various parameters influencing the combustion process. The study focuses on MoO3 as a hole transporting layer (HTL) for applications in organic photovoltaics (OPV). Via evolved gas analysis, it was found that fuel volatility occurs prior to the actual combustion reaction of the acetylacetonate based precursor, affecting the optimal oxidizer to fuel ratio. Moreover, close investigation showed that the high rate combustion reaction disappears with increasing surface to volume ratio. Nonetheless, thermal analysis performed on films suggests that with the right heating rate, an oxidative complete decomposition still occurs in films, exemplified by the film composition and specific morphological differences in the resulting layers and through analysis of the evolved components. Finally, the discussed synthesis route allows organic free, crystalline MoO3 films to be obtained affording organic solar cell devices with promising current density–voltage characteristics.
Materials | 2016
Ilona Maria Heckler; Jurgen Kesters; Maxime Defour; Morten Vesterager Madsen; Huguette Penxten; J. D’Haen; Bruno Van Mele; Wouter Maes; Eva Bundgaard
The stability of polymer solar cells (PSCs) can be influenced by the introduction of particular moieties on the conjugated polymer side chains. In this study, two series of donor-acceptor copolymers, based on bis(thienyl)dialkoxybenzene donor and benzo[c][1,2,5]thiadiazole (BT) or thiazolo[5,4-d]thiazole (TzTz) acceptor units, were selected toward effective device scalability by roll-coating. The influence of the partial exchange (5% or 10%) of the solubilizing 2-hexyldecyloxy by alternative 2-phenylethoxy groups on efficiency and stability was investigated. With an increasing 2-phenylethoxy ratio, a decrease in solar cell efficiency was observed for the BT-based series, whereas the efficiencies for the devices based on the TzTz polymers remained approximately the same. The photochemical degradation rate for PSCs based on the TzTz polymers decreased with an increasing 2-phenylethoxy ratio. Lifetime studies under constant sun irradiance showed a diminishing initial degradation rate for the BT-based devices upon including the alternative side chains, whereas the (more stable) TzTz-based devices degraded at a faster rate from the start of the experiment upon partly exchanging the side chains. No clear trends in the degradation behavior, linked to the copolymer structural changes, could be established at this point, evidencing the complex interplay of events determining PSCs’ lifetime.
Materials | 2017
Wouter Marchal; Inge Verboven; Jurgen Kesters; Boaz Moeremans; Christopher De Dobbelaere; Gilles Bonneux; Ken Elen; Bert Conings; Wouter Maes; Hans Gerd Boyen; Wim Deferme; Marlies K. Van Bael; An Hardy
The identification, fine-tuning, and process optimization of appropriate hole transporting layers (HTLs) for organic solar cells is indispensable for the production of efficient and sustainable functional devices. In this study, the optimization of a solution-processed molybdenum oxide (MoOx) layer fabricated from a combustion precursor is carried out via the introduction of zirconium and tin additives. The evaluation of the output characteristics of both organic photovoltaic (OPV) and organic light emitting diode (OLED) devices demonstrates the beneficial influence upon the addition of the Zr and Sn ions compared to the generic MoOx precursor. A dopant effect in which the heteroatoms and the molybdenum oxide form a chemical identity with fundamentally different structural properties could not be observed, as the additives do not affect the molybdenum oxide composition or electronic band structure. An improved surface roughness due to a reduced crystallinity was found to be a key parameter leading to the superior performance of the devices employing modified HTLs.
Macromolecular Rapid Communications | 2018
Geert Pirotte; Jurgen Kesters; Tom Cardeynaels; Pieter Verstappen; Jan D'Haen; Laurence Lutsen; Benoît Champagne; Dirk Vanderzande; Wouter Maes
Push-pull-type conjugated polymers applied in organic electronics do not always contain a perfect alternation of donor and acceptor building blocks. Misscouplings can occur, which have a noticeable effect on the device performance. In this work, the influence of homocoupling on the optoelectronic properties and photovoltaic performance of PDTSQxff polymers is investigated, with a specific focus on the quinoxaline acceptor moieties. A homocoupled biquinoxaline segment is intentionally inserted in specific ratios during the polymerization. These homocoupled units cause a gradually blue-shifted absorption, while the highest occupied molecular orbital energy levels decrease only significantly upon the presence of 75-100% of homocouplings. Density functional theory calculations show that the homocoupled acceptor unit generates a twist in the polymer backbone, which leads to a decreased conjugation length and a reduced aggregation tendency. The virtually defect-free PDTSQxff affords a solar cell efficiency of 5.4%, which only decreases substantially upon incorporating a homocoupling degree over 50%.