Papers by aranzazu aguirre
Energies
The outdoor performance monitoring of perovskite modules over 16 weeks is reported. Two different... more The outdoor performance monitoring of perovskite modules over 16 weeks is reported. Two different types of active perovskite layers were studied: one type contained formamidinium chloride (FACl) halide additives and the other contained no additives with the main purpose to investigate performance trends during the outdoor exposure of those type of devices. Long-term side-by-side outdoor testing of devices with and without halide additives was not implemented in the past and merits investigation in order to determine the impact of additives on perovskite performance and stability. Although the two types of modules displayed similar initial outdoor performance characteristics, their outdoor performance evolution differed. Different degradation rates between the modules with and without additives were obtained just after field installation. In particular, the modules with additives exhibited higher performance degradation under open-circuit loading conditions between current-voltage (I...
IMEC started up its activity on organic solar cells in 1998 and since 2005 this topic became one ... more IMEC started up its activity on organic solar cells in 1998 and since 2005 this topic became one of the key technologies of the Flemish Innovation Policy in the field of Photovoltaics. The aim of the paper is to present the overall Flemish approach and strategy to this field as well as to highlight the recent achievements of the Organic Photovoltaics Technology Program. The strategy of this program is built around three focal points: enhancement of the conversion efficiency, improvement of the cell stability and development of a printing technology to realize monolithic modules on a flexible foil. This strategy is being executed mainly within IMEC with its large expertise in the field of solar cell technology development and its associated lab, IMOMEC, and the University of Hasselt which has a strong background in synthesis and characterization of conjugated polymers. In addition, there is considerable analytical and modeling support by the University of Antwerp and the University Ghent.
Journal of Materials Chemistry A, 2012
A low band-gap copolymer PDTBTFV alternating bis-thienyl-(bis-alkoxy)-benzothiadiazole blocks wit... more A low band-gap copolymer PDTBTFV alternating bis-thienyl-(bis-alkoxy)-benzothiadiazole blocks with difluorovinylene units and its non-fluorinated counterpart PDTBTV have been synthesized and characterized as donor materials in bulk heterojunction (BHJ) solar cells with PCBM as the acceptor. The solar cells with the fluorinated polymer show better photovoltaic performances than those recorded with the non-fluorinated material. Comparative spectroscopic and computational studies, together with morphological, electrical and optical characterization of thin films, have been carried out to shed light on the reasons for the improvement of performances as induced by the double bond fluorination. Our study introduces the fluorinated double bond as a new conjugated unit in donor polymers for BHJ solar cells. Journal of Materials Chemistry A Paper low V oc and power conversion efficiency (PCE). The best performances were measured with a 2 : 7 (D : A) weight ratio. PDTBTFV shows better photovoltaic performances with signicantly higher V oc and PCE values (0.73-0.83 V and 0.83-1.24%, respectively) compared to PDTBTV (V oc 0.43-0.56 V and PCE 0.33-0.53%, respectively) for all the measured weight Scheme 1 Synthetic route for the monomer M3.
The Journal of Physical Chemistry A, 2011
Delayed emission from α-terthiophene (3T) and α-quinquethiophene (5T) in a perhydrotriphenylene (... more Delayed emission from α-terthiophene (3T) and α-quinquethiophene (5T) in a perhydrotriphenylene (PHTP) host is investigated. Delayed fluorescence for the lowest singlet excited state of 3T and 5T is detected at both low (80 K) and room temperatures. In addition, at low temperature, phosphorescence from 3T is observed with a lifetime of ∼100 μs. Comparison of the dependence of delayed fluorescence and phosphorescence on excitation intensity and time shows that delayed fluorescence does not originate from triplet--triplet annihilation. A dependence of the delayed fluorescence on atmospheric pressure indicates that it originates, at least partially, from complexes of photoexcited oligothiophene and molecular oxygen O(2).
Organic Electronics, 2011
Photoinduced changes in solids films of P3HT and PCPDTBT are studied in order to elucidate the in... more Photoinduced changes in solids films of P3HT and PCPDTBT are studied in order to elucidate the initial stage of photodegradation in polymer solar cells. We find that illumination of the polymers with either UV or visible light in the presence of air induces persistent radical cations on the polymer chains. The radical cations are identified by optical and electron paramagnetic resonance spectroscopy. The photoinduced charges are stable at room temperature for at least hours, but recombine rapidly upon removal of air from the sample chamber. We ascribe the persistent charges to P + ÀO 2 À charge pairs that are stabilized by chemical interactions between molecular oxygen and the polymer (P) Formation of persistent charges also takes place in the presence of the fullerene based electron acceptor PCBM.
Macromolecular Bioscience, 2013
Low band gap D-A conjugated PNs consisting of 2-ethylhexyl cyclopentadithiophene co-polymerized w... more Low band gap D-A conjugated PNs consisting of 2-ethylhexyl cyclopentadithiophene co-polymerized with 2,1,3-benzothiadiazole (for nano-PCPDTBT) or 2,1,3-benzoselenadiazole (for nano-PCPDTBSe) have been developed. The PNs are stable in aqueous media and showed no significant toxicity up to 1 mg · mL(-1) . Upon exposure to 808 nm light, the PNs generated temperatures above 50 °C. Photothermal ablation studies of the PNs with RKO and HCT116 colorectal cancer cells were performed. At concentrations above 100 µg · mL(-1) for nano-PCPDTBSe, cell viability was less than 20%, while at concentrations above 62 µg · mL(-1) for nano-PCPDTBT, cell viability was less than 10%. The results of this work demonstrate that low band gap D-A conjugated polymers 1) can be formed into nanoparticles that are stable in aqueous media; 2) are non-toxic until stimulated by IR light and 3) have a high photothermal efficiency.
The European Physical Journal Applied Physics, 2006
Efficient charge transfer between a newly synthesized low band gap (LBG) conjugated polymer and t... more Efficient charge transfer between a newly synthesized low band gap (LBG) conjugated polymer and the C60 derivative PCBM is demonstrated. Spectral and time-resolved photoluminescence (PL) measurements show strong quenching and charge separation in the picosecond time range. The charge transfer is further confirmed by light-induced electron paramagnetic resonance (EPR) measurements of both the positive polarons and the fullerene radicals, which can be resolved in high-frequency EPR. The potential for the LBG polymer to act as acceptor was examined in blends with the para-phenylene-vinylene polymer MDMO-PPV. No charge transfer, but instead energy transfer from MDMO-PPV to LBG occurs in these blends, as shown by PL spectroscopy.
Biomaterials, 2010
Fluorescence molecular imaging is rapidly increasing its popularity in image guided surgery appli... more Fluorescence molecular imaging is rapidly increasing its popularity in image guided surgery applications. To help develop its full surgical potential it remains a challenge to generate dual-emissive imaging agents that allow for combined visible assessment and sensitive camera based imaging. To this end, we now describe multispectral InP/ZnS quantum dots (QDs) that exhibit a bright visible green/yellow exciton emission combined with a long-lived far red defect emission. The intensity of the latter emission was enhanced by X-ray irradiation and allows for: 1) inverted QD density dependent defect emission intensity, showing improved efficacies at lower QD densities, and 2) detection without direct illumination and interference from autofluorescence.
Macromolecules, 2007
Mixtures of conjugated polymers and fullerenes command considerable attention for application in ... more Mixtures of conjugated polymers and fullerenes command considerable attention for application in organic solar cells. To increase their efficiency, the design of new materials that absorb at longer wavelengths is of substantial interest. We have prepared such low band gap polymers using the donor-acceptor route, which is based on the concept that the interaction between alternating donors and acceptors results in a compressed band gap. Furthermore, for application in photovoltaic devices, sufficient polymer solubility is required. We have prepared four low band gap conjugated polymers, with a bis(1-cyano-2-thienylvinylene)phenylene base structure, and achieved an excellent solubility by the introduction of long alkoxy and alkyl side chains. The polymers were synthesized via an oxidative polymerization. Their electronic properties were determined from electrochemical and optical measurements, which confirm that they indeed have a low band gap. In the blend of such a low band gap polymer with PCBM, evidence for efficient charge transfer was obtained from PL and EPR measurements. However, bulk heterostructure solar cells made of such blends display only low efficiencies, which is attributed to low charge carrier mobilities.
European Physical Journal-applied Physics, 2007
... of morphology of P3HT/PCBM films for organic solar cells 289 300 400 500 600 700 800 900 -0.2... more ... of morphology of P3HT/PCBM films for organic solar cells 289 300 400 500 600 700 800 900 -0.2 0.0 0.2 0.4 0.6 0.8 1.0 1.2 post-annealing as-produced P3HT/PCBM from THN P3HT/PCBM from CB P3HT/PCBM from DB P3HT from CB Absorbance Wavelength (nm) Fig. ...
Physical Chemistry Chemical Physics, 2008
The W-band continuous-wave electron paramagnetic resonance (EPR) analysis of chemically induced p... more The W-band continuous-wave electron paramagnetic resonance (EPR) analysis of chemically induced polarons in drop-cast and spin-coated polyphenylenevinylene-type and polythiophene-type polymer films reveals rhombic g tensors in both cases. The dependence of the W-band EPR signals on the orientation of the spin-coated films with respect to the magnetic field indicates a high degree of backbone alignment with the substrate and allows a partial assignment of the g tensor orientation. The derived molecular orientations of the polymer chains in the spin-coated films show clear differences between the two types of polymers. The proton hyperfine interactions obtained from X-band HYSCORE (hyperfine sublevel correlation) and Q- and W-band pulsed ENDOR (electron-nuclear double resonance) experiments are interpreted in terms of earlier theoretical studies on the extension of the polarons.
Macromolecules, 2007
Mixtures of conjugated polymers and fullerenes command considerable attention for application in ... more Mixtures of conjugated polymers and fullerenes command considerable attention for application in organic solar cells. To increase their efficiency, the design of new materials that absorb at longer wavelengths is of substantial interest. We have prepared such low band gap polymers using the donor-acceptor route, which is based on the concept that the interaction between alternating donors and acceptors results in a compressed band gap. Furthermore, for application in photovoltaic devices, sufficient polymer solubility is required. We have prepared four low band gap conjugated polymers, with a bis(1-cyano-2-thienylvinylene)phenylene base structure, and achieved an excellent solubility by the introduction of long alkoxy and alkyl side chains. The polymers were synthesized via an oxidative polymerization. Their electronic properties were determined from electrochemical and optical measurements, which confirm that they indeed have a low band gap. In the blend of such a low band gap polymer with PCBM, evidence for efficient charge transfer was obtained from PL and EPR measurements. However, bulk heterostructure solar cells made of such blends display only low efficiencies, which is attributed to low charge carrier mobilities.
Macromolecules, 2007
Mixtures of conjugated polymers and fullerenes command considerable attention for application in ... more Mixtures of conjugated polymers and fullerenes command considerable attention for application in organic solar cells. To increase their efficiency, the design of new materials that absorb at longer wavelengths is of substantial interest. We have prepared such low band gap polymers using the donor-acceptor route, which is based on the concept that the interaction between alternating donors and acceptors results in a compressed band gap. Furthermore, for application in photovoltaic devices, sufficient polymer solubility is required. We have prepared four low band gap conjugated polymers, with a bis(1-cyano-2-thienylvinylene)phenylene base structure, and achieved an excellent solubility by the introduction of long alkoxy and alkyl side chains. The polymers were synthesized via an oxidative polymerization. Their electronic properties were determined from electrochemical and optical measurements, which confirm that they indeed have a low band gap. In the blend of such a low band gap polymer with PCBM, evidence for efficient charge transfer was obtained from PL and EPR measurements. However, bulk heterostructure solar cells made of such blends display only low efficiencies, which is attributed to low charge carrier mobilities.
Macromolecules, 2007
Mixtures of conjugated polymers and fullerenes command considerable attention for application in ... more Mixtures of conjugated polymers and fullerenes command considerable attention for application in organic solar cells. To increase their efficiency, the design of new materials that absorb at longer wavelengths is of substantial interest. We have prepared such low band gap polymers using the donor-acceptor route, which is based on the concept that the interaction between alternating donors and acceptors results in a compressed band gap. Furthermore, for application in photovoltaic devices, sufficient polymer solubility is required. We have prepared four low band gap conjugated polymers, with a bis(1-cyano-2-thienylvinylene)phenylene base structure, and achieved an excellent solubility by the introduction of long alkoxy and alkyl side chains. The polymers were synthesized via an oxidative polymerization. Their electronic properties were determined from electrochemical and optical measurements, which confirm that they indeed have a low band gap. In the blend of such a low band gap polymer with PCBM, evidence for efficient charge transfer was obtained from PL and EPR measurements. However, bulk heterostructure solar cells made of such blends display only low efficiencies, which is attributed to low charge carrier mobilities.
Synthetic Metals, 2010
In this paper, we report a surfactant assisted processable organic dispersions of conducting form... more In this paper, we report a surfactant assisted processable organic dispersions of conducting form of polyaniline (PANI) with and without single wall carbon nanotubes (SWNTs). We used and compared the role of two anionic surfactants namely, sodium dodecylbenzene sulfonate (NaDBS) and sodium dodecyl sulfate (SDS). Based on our results, we believe that hydrophobic interactions between surfactant tails with SWNTs and the strong interactions between PANI-surfactant headgroups are very much likely to be responsible for stabilizing this three phase system in the organic solvent. In PANI-SWNT nanocomposites prepared using SDS, electronic like band of PANI is significantly affected as well as localization of the charge carriers is observed using UV-vis spectroscopy compared to nanocomposites prepared using NaDBS. These interactions are reflected in lower conductivity of the PAN-SWNT nanocomposites prepared using SDS indicating NaDBS has better doping effectiveness in PANI-SWNT nanocomposites. This facile route offers the processing of PANI-SWNT from single organic medium and in addition, eliminates the steps of de-doping, dissolution in suitable solvent and re-doping to regain the conductivity of the nanocomposite.
The pressure imposed to the environment by the use of fossil energy sources is too high and new a... more The pressure imposed to the environment by the use of fossil energy sources is too high and new alternatives are needed. Plastic (organic) photovoltaics is catching the attention of scientists because it offers interesting perspectives for large area/low cost/environmentally friendly/energy production. The widely used 3-D bulk heterojunction structure in organic solar cells comprises donor/acceptor blends, in which a soluble fullerene derivative (PCBM) acting as acceptor is embedded in a polymer matrix acting as an electron donor. An incident photon can create an exciton in the donor which can be separated into electron and hole at the donor acceptor interface. The electron is allowed in the acceptor while de hole stays in the donor. The light induced charge transfer gives rise to positive radicals on the polymer chains and negative radicals on the fullerene molecules. Electron Paramagnetic Resonance (EPR) is a powerful tool to monitor the charge transfer processes in these blends, and also allowed an in-depth investigation of the radical states in doped P3HT and MDMO-PPV, the standard polymers presently in use in state-of-the-art devices. Newly synthesized materials aimed to improve the available organic solar cells technologies, namely: materials with a better solubility (in environmentally more friendly solvents), acceptors (as alternative to PCBM) and materials with a lower band-gap (for better sunlight capture). Continuous wave EPR on composites of these conjugated polymers with PCBM allow the detection of efficient charge transfer from donor to acceptor and the discrimination of the g-tensor components of the polaron in the different polymers. Theoretical studies in PPV and thiophene positive radical states (P +) motivated the study of the polarons formed in MDMO-PPV and P3HT which can contribute to the development of more efficient photovoltaic devices. Extensive pulsed EPR (ESEEM, HSYCORE and pulsed ENDOR) experiments in a range of frequencies revealed hyperfine couplings with nuclei in the vicinity of the radicals formed and allowed the study of the orientation dependent interactions at the molecular level. These EPR results provide valuable information regarding the orientation of these polymers on the spin coating substrates and the extension of the polaron.
Physical Chemistry Chemical Physics, 2008
The W-band continuous-wave electron paramagnetic resonance (EPR) analysis of chemically induced p... more The W-band continuous-wave electron paramagnetic resonance (EPR) analysis of chemically induced polarons in drop-cast and spin-coated polyphenylenevinylene-type and polythiophene-type polymer films reveals rhombic g tensors in both cases. The dependence of the W-band EPR signals on the orientation of the spin-coated films with respect to the magnetic field indicates a high degree of backbone alignment with the substrate and allows a partial assignment of the g tensor orientation. The derived molecular orientations of the polymer chains in the spin-coated films show clear differences between the two types of polymers. The proton hyperfine interactions obtained from X-band HYSCORE (hyperfine sublevel correlation) and Q- and W-band pulsed ENDOR (electron-nuclear double resonance) experiments are interpreted in terms of earlier theoretical studies on the extension of the polarons.
Macromolecules, 2007
Mixtures of conjugated polymers and fullerenes command considerable attention for application in ... more Mixtures of conjugated polymers and fullerenes command considerable attention for application in organic solar cells. To increase their efficiency, the design of new materials that absorb at longer wavelengths is of substantial interest. We have prepared such low band gap polymers using the donor-acceptor route, which is based on the concept that the interaction between alternating donors and acceptors results in a compressed band gap. Furthermore, for application in photovoltaic devices, sufficient polymer solubility is required. We have prepared four low band gap conjugated polymers, with a bis(1-cyano-2-thienylvinylene)phenylene base structure, and achieved an excellent solubility by the introduction of long alkoxy and alkyl side chains. The polymers were synthesized via an oxidative polymerization. Their electronic properties were determined from electrochemical and optical measurements, which confirm that they indeed have a low band gap. In the blend of such a low band gap polymer with PCBM, evidence for efficient charge transfer was obtained from PL and EPR measurements. However, bulk heterostructure solar cells made of such blends display only low efficiencies, which is attributed to low charge carrier mobilities.
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Papers by aranzazu aguirre