| 1. |
- Farré, Yoann, et al.
(författare)
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Second Generation of DiketopyrrolopyrroleDyes for NiO based Dye-Sensitized Solar Cells
- 2016
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Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 120:15, s. 7923-7940
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Tidskriftsartikel (refereegranskat)abstract
- In this study, four new diketopyrrolopyrrole (DPP) sensitizers, with a dicarboxylated triphenylamine anchoring group for attachment to NiO, were prepared and their electronic absorption, emission and electrochemical properties were recorded. The nature of the electronic excited-states was also modeled with TD-DFT quantum chemistry calculations. The photovoltaic performances of these new dyes were characterized in NiO-based dye-sensitized solar cells (DSCs) with the classical iodide/triiodide and cobaltII/III-polypyridine electrolytes, in which they proved to be quite active. Laser spectroscopy on dye/NiO/electrolyte films gave evidence for ultrafast hole injection into NiO (0.2-10 ps time scales). For the dyes with an appended naphtalenediimide (NDI) acceptor unit, ultrafast electron transfer to the NDI dramatically prolonged the lifetime of the charge separated state NiO(+)/dye-, from the ps time scale to an average lifetime ≈ 0.25 ms, which is among the slowest charge recombinations ever reported for dye/NiO systems. This allowed for efficient regeneration by CoIIIpolypyridine electrolytes, which translated into much improved PV-performance compared to the DPP dyes without appended NDI. Overall, these results underscore the suitability of DPP as sensitizers for NiO-based photoelectrochemical devices for photovoltaic and photocatalysis.
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| 2. |
- Gennari, Marcello, et al.
(författare)
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Long-Lived Charge Separated State in NiO-Based p-Type Dye-Sensitized Solar Cells with Simple Cyclometalated Iridium Complexes
- 2014
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Ingår i: The Journal of Physical Chemistry Letters. - : American Chemical Society (ACS). - 1948-7185. ; 5:13, s. 2254-2258
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Tidskriftsartikel (refereegranskat)abstract
- Three new cyclometalated iridium complexes were prepared and investigated on nanocrystalline NiO cathodes. Nanosecond transient absorption spectroscopy experiments show they present a surprisingly slow geminate charge recombination upon excitation on NiO, representing thus the first examples of simple sensitizers with such feature. These complexes were used in dye-sensitized solar cells using nanocrystalline NiO film as semiconductor. The long-lived charge separated state of these Ir complexes make them compatible with other redox mediators than I-3(-)/I-, such as a cobalt electrolyte and enable to reach significantly high open circuit voltage.
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| 3. |
- Grabarz, Anna M., et al.
(författare)
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The impact of the heteroatom in a five-membered ring on the photophysical properties of difluoroborates
- 2019
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Ingår i: Dyes and pigments. - : Elsevier. - 0143-7208 .- 1873-3743. ; 170
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Tidskriftsartikel (refereegranskat)abstract
- A series of novel BF2 complexes, bearing a five-membered heterocyclic ring (with X = NMe, O, and S), were synthesized and characterized with a focus on the influence of atom exchange on the photophysical properties of both unsubstituted and dimethylamino derivatives. The experimental results show that the optical spectra substantially differ in both sets of dyes. In particular, the dimethylamino series are more strongly affected by heteroatom substitution, i.e., the insertion of X = O or X = S in lieu of X = NMe causes substantial bathochromic shifts of the absorption and emission bands, as well as marked changes in their topologies. In contrast, the optical spectra of the unsubstituted compounds undergo only relatively small red-shifts, and no variation of band shapes is observed. Moreover, the measured absorption spectra of the unsubstituted compounds bearing X = NMe and X = O are almost identical. Interestingly, the fluorescence yields of the dimethylamino derivatives are much larger (up to one order of magnitude) than those of the corresponding unsubstituted compounds. The experimental analyses are supported by state-of-the-art quantum chemistry calculations, which satisfactorily reproduced the experimental trends and provided further insights into the observed optical signatures.
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| 4. |
- Göransson, Erik, et al.
(författare)
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Long-Range Electron transfer in Zinc-Phthalocyanine-oligo(phenylene-ethynylene)-based donor-bridge-acceptor dyads
- 2012
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Ingår i: Inorganic Chemistry. - : American Chemical Society (ACS). - 0020-1669 .- 1520-510X. ; 51:21, s. 11500-11512
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Tidskriftsartikel (refereegranskat)abstract
- In the context of long-range electron transfer for solar energy conversion, we present the synthesis, photophysical, and computational characterization of two new zinc(II) phthalocyanine oligophenylene-ethynylene based donor-bride-acceptor dyads: ZnPc-OPE-AuP+ and ZnPc-OPE-C60. A gold(III) porphyrin and a fullerene has been used as electron accepting moieties, and the results have been compared to a previously reported dyad with a tin(IV) dichloride porphyrin as the electron acceptor (Fortage et al. Chem. Commun.2007, 4629). The results for ZnPc-OPE-AuP+ indicate a remarkably strong electronic coupling over a distance of more than 3 nm. The electronic coupling is manifested in both the absorption spectrum and an ultrafast rate for photoinduced electron transfer (kPET = 1.0 × 1012 s–1). The charge-shifted state in ZnPc-OPE-AuP+ recombines with a relatively low rate (kBET = 1.0 × 109 s–1). In contrast, the rate for charge transfer in the other dyad, ZnPc-OPE-C60, is relatively slow (kPET = 1.1 × 109 s–1), while the recombination is very fast (kBET ≈ 5 × 1010 s–1). TD-DFT calculations support the hypothesis that the long-lived charge-shifted state of ZnPc-OPE-AuP+ is due to relaxation of the reduced gold porphyrin from a porphyrin ring based reduction to a gold centered reduction. This is in contrast to the faster recombination in the tin(IV) porphyrin based system (kBET = 1.2 × 1010 s–1), where the excess electron is instead delocalized over the porphyrin ring.
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| 5. |
- Knysh, Iryna, et al.
(författare)
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Less is more: on the effect of benzannulation on the solid-state emission of difluoroborates
- 2021
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Ingår i: Journal of Materials Chemistry C. - : ROYAL SOC CHEMISTRY. - 2050-7526 .- 2050-7534. ; 9:44, s. 15820-15830
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Tidskriftsartikel (refereegranskat)abstract
- We investigate the emission properties of four organic dyes containing a strong electron-donating N(CH3)(2) group and an NBF2O-bearing heterocyclic moiety acting as the electron-accepting group. The four studied compounds differ in the number and positions of the fused benzo rings included in the heterocyclic moiety. They exhibit strong emission in solution, with fluorescence quantum yields (phi(f)) systematically exceeding 0.8 at least in one of the solvents used, regardless of the benzannulation architecture. The strong dipolar character, achieved by substitution with the N(CH3)(2) group and benzannulation, enhances the photoinduced charge transfer and appears to be an effective strategy to tune the photophysical properties of these dyes in solution. Indeed, red-shifted absorption spectra are obtained without deteriorating the emission properties. However, the present joint theory-experiment study clearly demonstrates that such a molecular design is not effective for solid-state applications, as only one derivative still exhibits significant emission in the crystalline form, namely the most compact one. We show that the combination of benzannulation in the presence of the strong amino donor leads to substantial changes in crystal packing and that a different network of intermolecular interactions can be found in the crystal. More specifically, going from the parent compound to its benzannulated derivatives induces a stronger pi MIDLINE HORIZONTAL ELLIPSIS pi stacking combined with multiple CHMIDLINE HORIZONTAL ELLIPSIS pi interactions involving the fused benzo rings and the hydrogen atoms of the dimethylamino group, which impedes efficient emission of the crystals.
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| 6. |
- Warnan, Julien, et al.
(författare)
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Acetylacetone anchoring group for NiO-based dye-sensitized solar cell
- 2014
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Ingår i: Dyes and pigments. - : Elsevier BV. - 0143-7208 .- 1873-3743. ; 105, s. 174-179
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Tidskriftsartikel (refereegranskat)abstract
- In this article, the viability of the first push pull (nitrophenyl and hexyl-thiophene as acceptor and donor unit respectively) sensitizer functionalized with acetylacetone (acac) anchoring group was assessed for application in p-type dye sensitized solar cells (Ni0-based). An effective synthetic strategy to introduce the acac directly to an aryl moiety was developed. Then, the UV visible absorption, emission and electrochemical properties of this new sensitizer were determined. FT-IR spectroscopy revealed an effective binding of the acac group to NiO surface while time-dependent density functional theory (TDDFT) calculations predicted a strong charge-transfer transition with no component of the LUMO centred on the acac. Ultrafast hole injection (<200 fs) from the dye excited state into the valence band (VB) of NiO was experimentally demonstrated by transient absorption spectroscopy studies. It was also shown that excitation of the sensitizer leads to the formation of a twisted intramolecular charge transfer (TICT) state. Finally, the photovoltaic performances of this dye were investigated in NiO based solar cells using the iodide/triiodide electrolyte. We measured promising power conversion efficiencies higher than that of the coumarin 043 benchmark reference albeit with a weaker light harvesting efficiency.
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| 7. |
- Zhang, Lei, et al.
(författare)
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Molecular-structure control of electron transferdynamics of push–pull porphyrins as sensitizers forNiO based dye sensitized solar cells
- 2016
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Ingår i: RSC Advances. - : Royal Society of Chemistry (RSC). - 2046-2069. ; 6:81, s. 77184-77194
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Tidskriftsartikel (refereegranskat)abstract
- Porphyrin dyes were synthesized for use in p-type (NiO) dye sensitized solar cells based on different designprinciples. One porphyrin was designed with a significant charge transfer character in the excited statebecause of push–pull effects of the substituents. Another porphyrin had instead an appended NDIacceptor group (NDI ¼ naphthalene diimide). The dyes were characterized by spectroscopic,electrochemical and DFT methods. Solar cells based on sensitized, meso-porous NiO showed ratherpoor performance compared to other organic dyes, but with a clear improvement for the dye with theNDI acceptor. Ultrafast transient absorption spectroscopy and nanosecond laser photolysis showed thathole injection into NiO was followed by unusually rapid charge recombination, predominantly ona 50–100 ps time scale, which is likely the main reason for the poor photovoltaic performance. Againthe porphyrin with the NDI group showed a more long-lived charge separation that should lead to betterdye regeneration in a solar cell, which can explain its better photovoltaic performance.
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