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| 2. |
- Admassie, Shimelis, et al.
(författare)
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Electrochemical and optical studies of the band gaps of alternating polyfluorene copolymers
- 2006
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Ingår i: Synthetic metals. - : Elsevier BV. - 0379-6779 .- 1879-3290. ; 156:7-8, s. 614-623
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Tidskriftsartikel (refereegranskat)abstract
- The electrochemical and optical properties of a series of alternating polyfluorene copolymers with low band gaps were determined. These polymers incorporated fluorene units alternating with groups including electron-withdrawing (A) and electron-donating (D) groups in donor-acceptor-donor (DAD) sequence to achieve the lowering of band gaps. The polymers were solvent-casted on platinum disk electrode and the band gaps were estimated from cyclic voltammetry (CV). These values were compared with values obtained from optical absorption measurements. Although the electrochemically determined band gaps were found to be slightly higher than the optical band gap in most cases, values are well correlated. The values of the band gaps determined range from 2.1 to 1.3 eV. © 2006 Elsevier B.V. All rights reserved.
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| 3. |
- Ajjan, Fátima, 1986-, et al.
(författare)
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Doped Conjugated Polymer Enclosing a Redox Polymer : Wiring Polyquinones with Poly(3,4‐Ethylenedioxythiophene)
- 2020
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Ingår i: Advanced Energy and Sustainability Research. - : John Wiley & Sons. - 2699-9412. ; 1:2
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Tidskriftsartikel (refereegranskat)abstract
- The mass implementation of renewable energies is limited by the absence of efficient and affordable technology to store electrical energy. Thus, the development of new materials is needed to improve the performance of actual devices such as batteries or supercapacitors. Herein, the facile consecutive chemically oxidative polymerization of poly(1-amino-5-chloroanthraquinone) (PACA) and poly(3,4-ethylenedioxythiophene (PEDOT) resulting in a water dispersible material PACA-PEDOT is shown. The water-based slurry made of PACA-PEDOT nanoparticles can be processed as film coated in ambient atmosphere, a critical feature for scaling up the electrode manufacturing. The novel redox polymer electrode is a nanocomposite that withstands rapid charging (16 A g−1) and delivers high power (5000 W kg−1). At lower current density its storage capacity is high (198 mAh g−1) and displays improved cycling stability (60% after 5000 cycles). Its great electrochemical performance results from the combination of the redox reversibility of the quinone groups in PACA that allows a high amount of charge storage via Faradaic reactions and the high electronic conductivity of PEDOT to access to the redox-active sites. These promising results demonstrate the potential of PACA-PEDOT to make easily organic electrodes from a water-coating process, without toxic metals, and operating in non-flammable aqueous electrolyte for large scale pseudocapacitors.
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| 4. |
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| 5. |
- Bian, Qingzhen, 1988-, et al.
(författare)
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Vibronic coherence contributes to photocurrent generation in organic semiconductor heterojunction diodes
- 2020
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Ingår i: Nature Communications. - : NATURE PUBLISHING GROUP. - 2041-1723. ; 11:1
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Tidskriftsartikel (refereegranskat)abstract
- Charge separation dynamics after the absorption of a photon is a fundamental process relevant both for photosynthetic reaction centers and artificial solar conversion devices. It has been proposed that quantum coherence plays a role in the formation of charge carriers in organic photovoltaics, but experimental proofs have been lacking. Here we report experimental evidence of coherence in the charge separation process in organic donor/acceptor heterojunctions, in the form of low frequency oscillatory signature in the kinetics of the transient absorption and nonlinear two-dimensional photocurrent spectroscopy. The coherence plays a decisive role in the initial 200 femtoseconds as we observe distinct experimental signatures of coherent photocurrent generation. This coherent process breaks the energy barrier limitation for charge formation, thus competing with excitation energy transfer. The physics may inspire the design of new photovoltaic materials with high device performance, which explore the quantum effects in the next-generation optoelectronic applications.
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| 6. |
- Campoy-Quiles, M., et al.
(författare)
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On the determination of anistropy in polymer thin films : A comparative study of optical techniques
- 2008
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Ingår i: Physica Status Solidi. C: Current Topics in Solid State Physics. - Weinheim, Germany : Wiley-VCH Verlagsgesellschaft. - 1862-6351. ; 5:5, s. 1270-1273
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Tidskriftsartikel (refereegranskat)abstract
- We have used seven different techniques to measure the anisotropic refractive index of poly(vinylcarbazole) films. These techniques are: two types of variable angle spectroscopic ellipsometry (VASE) with multiple sample analysis, Interference enhanced VASE, Transmittance combined with VASE, Polarised Reflectance, beta-scan VASE, and prism coupling. We have found the average ordinary and extraordinary indices at 633 nm to be no = nTE = 1.675 ± 0.008, and ne = nTM = 1.722 ± 0.018, respectively, consistent amongst methods and conclusive on the magnitude of Δn in polymer films.
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| 7. |
- Chen, Miaoxiang, 1962-, et al.
(författare)
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High carrier mobility in low band gap polymer-based field-effect transistors
- 2005
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 87:25, s. 252105-1-252105-3
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Tidskriftsartikel (refereegranskat)abstract
- A conjugated polymer with a low band gap of 1.21 eV, i.e., absorbing infrared light, is demonstrated as active material in field-effect transistors (FETs). The material consists of alternating fluorene units and low band gap segments with electron donor-acceptor-donor units composed of two electron-donating thiophene rings attached on both sides of a thiadiazolo-quinoxaline electron-acceptor group. The polymer is solution-processable and air-stable; the resulting FETs exhibit typical p-channel characteristics and field-effect mobility of 0.03 cm2 V−1 s−1.
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| 8. |
- De, Swati, et al.
(författare)
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Exciton Dynamics in Alternating Polyfluorene/Fullerene Blends
- 2008
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Ingår i: Journal of Chemical Physics. - College Park, MD, United States : American Institute of Physics (AIP). - 0021-9606 .- 1089-7690. ; 350:1-3, s. 14-22
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Tidskriftsartikel (refereegranskat)abstract
- Exciton dynamics in alternating copolymer/fullerene solar cell blends have been investigated using femtosecond transient absorption spectroscopy. The acceptor concentrations have been varied over a wide range. Experimental data, kinetic modeling and simulations, all indicate that the efficiency of exciton conversion to charges is 100% even at acceptor concentrations as low as 20 wt%. The reported dependence of solar cell efficiency on fullerene concentration may thus arise from other factors. However, there exists an acceptor concentration threshold (5 wt%) below which a substantial fraction of the excitations remain unquenched. The results, we believe are very relevant to optimization of performance efficiency by clever manipulation of morphology. We have also observed exciton–exciton energy transfer in these blends at low acceptor concentrations.
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| 9. |
- De, Swati, et al.
(författare)
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Geminate charge recombination in alternating polyfluorene copolymer/fullerene blends
- 2007
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Ingår i: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 0002-7863 .- 1520-5126. ; 129:27, s. 8466-8472
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Tidskriftsartikel (refereegranskat)abstract
- By measuring excited state and charge dynamics in blends of an alternating polyfluorene copolymer and fullerene derivative over nine orders in time and two orders in light intensity, we have monitored the light-induced processes from ultrafast charge photogeneration to much slower decay of charges by recombination. We find that at low light intensities relevant to solar cell operation relatively fast (∼30 ns) geminate recombination is the dominating charge decay process, while nongeminate recombination has a negligible contribution. The conclusion of our work is that under solar illumination conditions geminate recombination of charges may be directly competing with efficient charge collection in polymer/fullerene solar cells. © 2007 American Chemical Society.
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| 10. |
- Fernandez-Benito, Amparo, et al.
(författare)
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Green and Scalable Biopolymer-Based Aqueous Polyelectrolyte Complexes for Zinc-Ion Charge Storage Devices
- 2023
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Ingår i: ChemElectroChem. - : WILEY-V C H VERLAG GMBH. - 2196-0216. ; 10:2
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Tidskriftsartikel (refereegranskat)abstract
- Green and scalable materials are essential to fulfill the need of electrification for transitioning into a fossil-fuels free society, and sustainability is a requirement for all new technologies. Rechargeable batteries are one of the most important elements for electrification, enabling the transition to mobile electronics, electrical vehicles and grid storage. We here report synthesis and characterization of polyelectrolyte complexes of alginate and chitosan, both biopolymers deriving from the sea, for transport of zinc ions in hydrogel electrolytes. We have used vibrational spectroscopy, thermal measurements and microscopy, as well as transport measurements with ohmic or blocking contacts. The transference number for zinc ions is close to 1, the conductivity is approximate to 10 mS/cm, with stability at Zn interfaces seen through 7000 cycles in symmetric zinc//zinc cell. A zinc ion aqueous electrolyte was prepared from blends of chitosan and alginate, by using a simple and scalable route. These green zinc ion electrolytes exhibit a stability window up to 2 V, a zinc ion transference number close to 1, and electrochemical cyclability over 7000 cycles at interfaces to zinc. This biologically derived polyelectrolyte complex offers many possibilities for optimizing transport and stability at electrode interfaces.image
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