| 1. |
- Zhuang, Wenliu, 1979, et al.
(författare)
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Influence of Incorporating Different Electron-Rich Thiophene-Based Units on the Photovoltaic Properties of Isoindigo-Based Conjugated Polymers: An Experimental and DFT Study
- 2013
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Ingår i: Macromolecules. - : American Chemical Society (ACS). - 1520-5835 .- 0024-9297. ; 46:21, s. 8488-8499
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Tidskriftsartikel (refereegranskat)abstract
- A series of novel donor–acceptor conjugated alternating copolymers based on the isoindigo acceptor moiety have been designed, synthesized, and characterized, in order to explore the potential of isoindigo for efficient donor materials with high photovoltages in solar cells. We have systematically investigated and discussed the effect of combining different electron-rich thiophene-based units on the structural, optical, electronic, and photovoltaic properties of the resulting polymers. Morphological studies and quantum-chemical calculations are carried out to gain insights into the different properties. The power conversion efficiencies (PCEs) of the solar cells based on these polymers are increased step by step by over 3-fold through a rational structural modification. Among them, PBDTA-MIM shows a PCE of 5.4%, which is to our knowledge the best result achieved among isoindigo-based polymers for solar cells combined with PC61BM as the acceptor using the conventional device configuration. Our results further emphasize the use of isoindigo as an effective acceptor unit and highlight the importance of carefully choosing appropriate chemical structure to design efficient donor–acceptor polymers for organic solar cells. In addition, the resulting low optical gaps, the promising PCEs with PC61BM as the acceptor, and the good open-circuit voltages (up to 0.8 V) synergistically demonstrate the potential of this class of polymers as donor materials for bottom subcells in organic tandem solar cells.
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| 2. |
- Dang, Dongfeng, 1988, et al.
(författare)
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Enhanced Photovoltaic Performance of Indacenodithiophene-Quinoxaline Copolymers by Side- Chain Modulation
- 2014
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Ingår i: Advanced Energy Materials. - : Wiley. - 1614-6840 .- 1614-6832. ; 4:15, s. Art. no. 1400680-
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Tidskriftsartikel (refereegranskat)abstract
- Two pairs of indacenodithiophene (IDT) and quinoxaline-based copolymers with meta- or para-hexyl-phenyl side chains on the IDT unit are synthesized. The meta-substituted polymers offer better solubility, higher molecular weight for both fluorinated and non-fluorinated copolymers, and a superior photovoltaic performance with a power conversion efficiency of 7.8%. The side-chain design strategy presented is an efficient way to produce high performance conjugated polymers for organic electronics.
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| 3. |
- George, Zandra, 1985, et al.
(författare)
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The Influence of Alkoxy Substitutions on the Properties of Diketopyrrolopyrrole-Phenyl Copolymers for Solar Cells
- 2013
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Ingår i: Materials. - : MDPI AG. - 1996-1944. ; 6:7, s. 3022-3034
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Tidskriftsartikel (refereegranskat)abstract
- A previously reported diketopyrrolopyrrole (DPP)-phenyl copolymer is modified by adding methoxy or octyloxy side chains on the phenyl spacer. The influence of these alkoxy substitutions on the physical, opto-electronic properties, and photovoltaic performance were investigated. It was found that the altered physical properties correlated with an increase in chain flexibility. Well-defined oligomers were synthesized to verify the observed structure-property relationship. Surprisingly, methoxy substitution on the benzene spacer resulted in higher melting and crystallization temperatures in the synthesized oligomers. This trend is not observed in the polymers, where the improved interactions are most likely counteracted by the larger conformational possibilities in the polymer chain upon alkoxy substitution. The best photovoltaic performance was obtained for the parent polymer: fullerene blends whereas the modifications on the other two polymers result in reduced open-circuit voltage and varying current densities under similar processing conditions. The current densities could be related to different polymer: fullerene blend morphologies. These results show that supposed small structural alterations such as methoxy substitution already significantly altered the physical properties of the parent polymer and also that oligomers and polymers respond divergent to structural alterations made on a parent structure.
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| 4. |
- Gray, Victor, 1988, et al.
(författare)
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Photophysical characterization of the 9,10-disubstituted anthracene chromophore and its applications in triplet-triplet annihilation photon upconversion
- 2015
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Ingår i: Journal of Materials Chemistry C. - : Royal Society of Chemistry (RSC). - 2050-7526 .- 2050-7534. ; 3:42, s. 11111-11121
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Tidskriftsartikel (refereegranskat)abstract
- Molecules based on anthracene are commonly used in applications such as OLEDs and triplet-triplet annihilation upconversion. In future design of blue emitting materials it is useful to know which part of the molecule can be altered in order to obtain new physical properties without losing the inherent optical properties. We have studied the effect of substitution of 9,10-substituted anthracenes. Eight anthracenes with aromatic phenyl and thiophene substituents were synthesised, containing both electron donating and accepting groups. The substitutions were found to affect the UV/Vis absorption only to a small extent, however the fluorescence properties were more affected with the thiophene substituents that decreased the fluorescence quantum yield from unity to
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| 5. |
- Jarvid, Markus, 1985, et al.
(författare)
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High electron affinity: a guiding criterion for voltage stabilizer design
- 2015
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Ingår i: Journal of Materials Chemistry A. - : Royal Society of Chemistry (RSC). - 2050-7488 .- 2050-7496. ; 3:14, s. 7273-7286
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Tidskriftsartikel (refereegranskat)abstract
- Voltage stabilizers are an emerging class of additives that enhance the dielectric strength of an insulating polymer such as polyethylene. Several partially conflicting reports ascribe the stabilizing effect to either a high electron affinity or low ionization potential of the additive. Here, we report a clear correlation of the electron affinity and to a lesser extent the EHOMO–ELUMO difference of various voltage stabilizers with electrical tree initiation in cross-linked polyethylene. To facilitate a fair evaluation, the voltage-stabilizing efficiency of a set of 13 previously reported voltage stabilizers, which strongly differ in their chemical composition, is compared at equal stabilizer concentration and equivalent test methodology. These results are correlated with the electron affinity and EHOMO–ELUMO difference, as obtained from density functional theory (DFT) modeling, which agreed well with available literature values. Moreover, based on the here established strong correlation between dielectric strength and electron affinity, a new molecule with exceptionally high electron affinity is selected from the extended literature on organic photovoltaics. This malononitrile–benzothiadiazole–triarylamine based molecule with a high electron affinity of 3.4 eV gives rise to a 148% increase in tree initiation field compared to 40% obtained using anthracene, one of the most efficient previously reported voltage-stabilizers, under equivalent test conditions. Thus, we here propose to use the electron affinity as a guiding criterion for identifying novel high-efficiency voltage stabilizers, which opens up the vast library of organic semiconductors as potential candidates, as well as associated synthesis routines for the design of yet unexplored materials.
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| 6. |
- Kroon, Renee, 1982, et al.
(författare)
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Effect of electron-withdrawing side chain modifications on the optical properties of thiophene-quinoxaline acceptor based polymers
- 2013
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Ingår i: Polymer. - : Elsevier BV. - 0032-3861. ; 54:4, s. 1285-1288
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Tidskriftsartikel (refereegranskat)abstract
- Four new thiophene-quinoxaline acceptor based polymers have been synthesized. The parent thiophene-quinoxaline acceptor based copolymer was modified by introducing different electron-withdrawing groups adjacent to the thiophene side group. The effect on the physical, electrochemical and optical properties of the polymer series is discussed with respect to the parent thiophene-quinoxaline acceptor based polymer. The side chain carbonyl from one modified monomer could conveniently be transformed to either a difluoromethylene or an -ylidene malononitrile group via carbonyl transformations. For all polymers incorporating an electron-withdrawing side group both the HOMO and especially the LUMO were significantly shifted away from vacuum while all exhibit enhanced light harvesting ability. Especially the incorporation of an -ylidine malononitrile side group increases both the spectral coverage and absorption coefficient. Incorporation of a difluoromethylene side group resulted in a twofold increase of the molecular weight compared to the parent polymer structure.
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| 7. |
- Kuisma, Mikael Juhani, 1984, et al.
(författare)
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Comparative Ab-Initio Study of Substituted Norbornadiene-Quadricyclane Compounds for Solar Thermal Storage
- 2016
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Ingår i: Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 120:7, s. 3635-3645
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Tidskriftsartikel (refereegranskat)abstract
- Molecular photoswitches that are capable of storing solar energy, so-called molecular solar thermal storage systems, are interesting candidates for future renewable energy applications. In this context, substituted norbornadiene-quadricyclane systems have received renewed interest due to recent advances in their synthesis. The optical, thermodynamic, and kinetic properties of these systems can vary dramatically depending on the chosen substituents. The molecular design of optimal compounds therefore requires a detailed understanding of the effect of individual substituents as well as their interplay. Here, we model absorption spectra, potential energy storage, and thermal barriers for back-conversion of several substituted systems using both single-reference (density functional theory using PBE, B3LYP, CAM-B3LYP, M06, M06-2x, and M06-L functionals as well as MP2 calculations) and multireference methods (complete active space techniques). Already the diaryl substituted compound displays a strong red shift compared to the unsubstituted system, which is shown to result from the extension of the conjugated pi-system upon substitution. Using specific donor/acceptor groups gives rise to a further albeit relatively smaller red-shift. The calculated storage energy is found to be rather insensitive to the specific substituents, although solvent effects are likely to be important and require further study. The barrier for thermal back-conversion exhibits strong multireference character and as a result is noticeably correlated with the red-shift. Two possible reaction paths for the thermal back-conversion of diaryl substituted quadricyclane are identified and it is shown that among the compounds considered the path via the acceptor side is systematically favored. Finally, the present study establishes the basis for high-throughput screening of norbornadiene-quadricyclane compounds as it provides guidelines for the level of accuracy that can be expected for key properties from several different techniques.
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| 8. |
- Kuisma, Mikael Juhani, 1984, et al.
(författare)
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Optimization of Norbornadiene Compounds for Solar Thermal Storage by First-Principles Calculations
- 2016
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Ingår i: ChemSusChem. - : Wiley. - 1864-5631 .- 1864-564X. ; 9:14, s. 1786-1794
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Tidskriftsartikel (refereegranskat)abstract
- Molecular photoswitches capable of storing solar energy are interesting candidates for future renewable energy applications. Here, using quantum mechanical calculations, we carry out a systematic screening of crucial optical (solar spectrum match) and thermal (storage energy density) properties of 64 such compounds based on the norbornadiene-quadricyclane system. Whereas a substantial number of these molecules reach the theoretical maximum solar power conversion efficiency, this requires a strong red-shift of the absorption spectrum, which causes undesirable absorption by the photoisomer as well as reduced thermal stability. These compounds typically also have a large molecular mass, leading to low storage densities. By contrast, single-substituted systems achieve a good compromise between efficiency and storage density, while avoiding competing absorption by the photo-isomer. This establishes guiding principles for the future development of molecular solar thermal storage systems.
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| 9. |
- Lennartson, Anders, 1980, et al.
(författare)
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Tuning the photochemical properties of the fulvalene-tetracarbonyl-diruthenium system
- 2016
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Ingår i: Dalton Transactions. - : Royal Society of Chemistry (RSC). - 1477-9226 .- 1477-9234. ; 45:21, s. 8740-8744
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Tidskriftsartikel (refereegranskat)abstract
- In a Molecular Solar-Thermal Energy Storage (MOST) system, solar energy is converted to chemical energy using a compound that undergoes reversible endothermic photoisomerization. The high-energy photoisomer can later be converted back to the parent compound and the excess energy is released as heat. One of the most studied MOST systems is based on fulvalene-tetracarbonyl-diruthenium, and this paper demonstrates, for the first time, the possibility to tune the photochemical properties of this system by positive steric hindrance working on the fulvalene unit.
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| 10. |
- Lundin, Angelica, 1971, et al.
(författare)
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A mechanistic investigation of ethylene oxide hydrolysis to ethanediol
- 2007
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Ingår i: Journal of Physical Chemistry A. - : American Chemical Society (ACS). - 1089-5639 .- 1520-5215. ; 111:37, s. 9087-9092
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Tidskriftsartikel (refereegranskat)abstract
- The B3LYP/6-311 +G(d,p) description is employed to study the heterolytic ring opening mechanisms under microsolvation conditions for ethylene oxide in acidic, neutral, and alkaline environments. In acid and alkaline media, a concerted trans S(N)2 reaction is strongly favored as compared to the corresponding cis reaction. The importance of the nucleophile, water in acidic media and hydroxide ion in alkaline media, for lowering the activation enthalpy is emphasized and activation energies of similar to 80 and similar to 60 kJ mol(-1) are obtained under acid and alkaline conditions, respectively. Under neutral conditions, the trans SN2 mechanism becomes inaccessible because it invokes the formation of a transient HI and OH- pair across the 1,2-ethanediol molecule. Rather, epoxide ring opening is achieved by hydrolysis of a single water molecule. The latter mechanism displays significantly greater activation enthaply (205 kJ mol(-1)) than those in acid and alkaline environments. This is in agreement with experiment. Product distributions of simple olefins in neutral aqueous media, as well as the detrimental impact of acid/base conditions for the selectivity of epoxidation catalysts in aqueous media, are discussed.
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