| 1. |
- Admassie, Shimelis, et al.
(author)
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Electrochemical and optical studies of the band gaps of alternating polyfluorene copolymers
- 2006
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In: Synthetic metals. - : Elsevier BV. - 0379-6779 .- 1879-3290. ; 156:7-8, s. 614-623
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Journal article (peer-reviewed)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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| 2. |
- Admassie, Shimelis, et al.
(author)
-
Electrochemical and optical studies of the band gaps of alternating polyfluorene copolymers
- 2006
-
In: Synthetic Metals. ; 156:7-8, s. 614-623
-
Journal article (peer-reviewed)abstract
- The electrochem. and optical properties of alternating polyfluorene copolymers with low band gaps were detd. 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 Pt disk electrode and the band gaps were estd. from cyclic voltammetry (CV). These values were compared with values obtained from optical absorption measurements. Although the electrochem. detd. band gaps are slightly higher than the optical band gap in most cases, values are well correlated. The values of the band gaps detd. range from 2.1 to 1.3 eV. [on SciFinder (R)]
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| 3. |
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| 4. |
- Chen, Miaoxiang, 1962-, et al.
(author)
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High carrier mobility in low band gap polymer-based field-effect transistors
- 2005
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In: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 87:25, s. 252105-1-252105-3
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Journal article (peer-reviewed)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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| 5. |
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| 6. |
- Gadisa, Abay, et al.
(author)
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Red and near infrared polarized light emission from polyfluorene copolymer based light emitting diodes
- 2007
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In: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 90:11, s. 113510-
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Journal article (peer-reviewed)abstract
- The authors report polarized red, electroluminescence peak at 705 nm and near infrared, electroluminescence peak at 950 nm, light emission from light emitting diodes based on two polyfluorene copolymers. The copolymers are synthesized from a fluorene monomer combined with donor-acceptor-donor comonomers and designed to have a low band gap and form birefringent liquid crystalline phases. Emission occurs from aligned thin films of polymer layers. The emissive layers are aligned by spin coating on a layer of rubbed conducting polymer poly(3,4-ethylene dioxythiophene)-poly(styrene sulphonate) and thermally converted into glassy nematic liquid crystalline state.
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| 7. |
- Gadisa, Abay, et al.
(author)
-
Red and near infrared polarized light emissions from polyfluorene copolymer based light emitting diodes
- 2007
-
In: Appl. Phys. Lett. FIELD Full Journal Title:Applied Physics Letters. ; 90:11, s. 113510/1-113510/3
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Journal article (peer-reviewed)abstract
- The authors report polarized red, electroluminescence peak at 705 nm and near IR, electroluminescence peak at 950 nm, light emission from light emitting diodes based on two polyfluorene copolymers. The copolymers are synthesized from a fluorene monomer combined with donor-acceptor-donor comonomers and designed to have a low band gap and form birefringent liq. cryst. phases. Emission occurs from aligned thin films of polymer layers. The emissive layers are aligned by spin coating on a layer of rubbed conducting polymer poly(3,4-ethylene dioxythiophene)-poly(styrene sulfonate) and thermally converted into glassy nematic liq. cryst. state. [on SciFinder (R)]
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| 8. |
- Gadisa, Abay, et al.
(author)
-
Stoichiometry dependence of charge transport in polymer/methanofullerene and polymer/C70 derivative based solar cells
- 2006
-
In: Organic electronics. - : Elsevier BV. - 1566-1199. ; 7:4, s. 195-204
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Journal article (peer-reviewed)abstract
- Charge transport in a near infrared absorbing polyfluorene copolymer (APFO-Green1) and its blends with methanofullerene [6,6]-phenyl C61-butyric acid methyl ester (PCBM), and 3′-(3,5-bis-trifluoromethylphenyl)-1′-(4-nitrophenyl)pyrazolino[70]fullerene (BTPF70) is reported. PCBM and BTPF70 are electron acceptor and transporting molecules in polymer based solar cells. The BTPF70 has emerged as a new electron acceptor molecule that provides adequate exciton dissociation when blended with the low band gap polyfluorene copolymer APFO-Green1. Electron transport in both net PCBM and BTPF70 films are subjected to positional and energetic disorder, with the degree of disorder being more pronounced in BTPF70. On the other hand, mixing PCBM with conjugated polymers usually leads to increased hole mobility. We have investigated and compared the acceptor concentration dependence of charge transport in APFO-Green1/PCBM and APFO-Green1/BTPF70 blend films. For better understanding of the charge transport in the heterojunction films, the field and temperature dependence of hole transport in pure APFO-Green1 films has also been studied. It is observed that the behavior of hole mobility in the blend layer is sensitive to the acceptor type. For APFO-Green1/PCBM hole only devices, the hole mobility attains a local maximum at 67 wt.% of PCBM, while on the contrary mixing any amount of BTPF70 with APFO-Green1 results into degradation of hole transport. Electron transport in both blends, however, increases monotonically as a function of acceptor loading.
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| 9. |
- Gadisa, Abay, et al.
(author)
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Stoichiometry dependence of charge transport in polymer/methanofullerene and polymer/C70 derivative based solar cells
- 2006
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In: Organic Electronics. ; 7:4, s. 195-204
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Journal article (peer-reviewed)abstract
- Charge transport in a near IR absorbing polyfluorene copolymer (APFO-Green1) and its blends with methanofullerene [6,6]-Ph C61-butyric acid Me ester (PCBM), and 3'-(3,5-bis-trifluoromethylphenyl)-1'-(4-nitrophenyl)pyrazolino[70]fullerene (BTPF70) is reported. PCBM and BTPF70 are electron acceptor and transporting mols. in polymer based solar cells. The BTPF70 has emerged as a new electron acceptor mol. that provides adequate exciton dissocn. when blended with the low band gap polyfluorene copolymer APFO-Green1. Electron transport in both net PCBM and BTPF70 films are subjected to positional and energetic disorder, with the degree of disorder being more pronounced in BTPF70. On the other hand, mixing PCBM with conjugated polymers usually leads to increased hole mobility. We have investigated and compared the acceptor concn. dependence of charge transport in APFO-Green1/PCBM and APFO-Green1/BTPF70 blend films. For better understanding of the charge transport in the heterojunction films, the field and temp. dependence of hole transport in pure APFO-Green1 films has also been studied. It is obsd. that the behavior of hole mobility in the blend layer is sensitive to the acceptor type. For APFO-Green1/PCBM hole only devices, the hole mobility attains a local max. at 67 wt.% of PCBM, while on the contrary mixing any amt. of BTPF70 with APFO-Green1 results into degrdn. of hole transport. Electron transport in both blends, however, increases monotonically as a function of acceptor loading. [on SciFinder (R)]
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| 10. |
- Inganaes, Olle, et al.
(author)
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Alternating fluorene copolymer-fullerene blend solar cells
- 2005
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In: Optical Science and Engineering. ; 99, s. 387-402
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Journal article (peer-reviewed)abstract
- We present a new class of alternating fluorene copolymers, which can be combined with a fullerene acceptor, to make polymer blends suitable for photovoltaic energy conversion. By choice of comonomers in the polymer, it is possible to engineer the optical absorption spectrum and to cover the wavelength range down to 900 nm. The transport properties of the polymers investigated so far are competitive with other polymers used in polymer solar cells and the mixing of polymers with acceptors in the form of fullerenes is extensive. These polymers are therefore of interest in the future developments of high-performance polymer solar cells. [on SciFinder (R)]
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| 11. |
- Inganäs, Olle, 1951-, et al.
(author)
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Alternating fluorene copolymer/fullerene blend solar cells
- 2005. - 1
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In: Organic Photovoltaics. - Boca Raton, FL, USA : CRC Press. - 082475963X - 9780824759636 ; , s. 387-402
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Book chapter (other academic/artistic)abstract
- Recently developed organic photovoltaics (OPVs) show distinct advantages over their inorganic counterparts due to their lighter weight, flexible shape, versatile materials synthesis and device fabrication schemes, and low cost in large-scale industrial production. Although many books currently exist on general concepts of PV and inorganic PV materials and devices, few are available that offer a comprehensive overview of recently fast developing organic and polymeric PV materials and devices.Organic Photovoltaics: Mechanisms, Materials, and Devicesfills this gap. The book provides an international perspective on the latest research in this rapidly expanding field with contributions from top experts around the world. It presents a unified approach comprising three sections: General Overviews; Mechanisms and Modeling; and Materials and Devices. Discussions include sunlight capture, exciton diffusion and dissociation, interface properties, charge recombination and migration, and a variety of currently developing OPV materials/devices. The book also includes two forewords: one by Nobel Laureate Dr. Alan J. Heeger, and the other by Drs. Aloysius Hepp and Sheila Bailey of NASA Glenn Research Center.Organic Photovoltaics equips students, researchers, and engineers with knowledge of the mechanisms, materials, devices, and applications of OPVs necessary to develop cheaper, lighter, and cleaner renewable energy throughout the coming decades.
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| 12. |
- Lindgren, Lars Johan, 1977, et al.
(author)
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Synthesis, Characterization, and Devices of a Series of Alternating Copolymers for Solar Cells
- 2009
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In: CHEMISTRY OF MATERIALS. - : American Chemical Society (ACS). - 0897-4756 .- 1520-5002. ; 21:15, s. 3491-3502
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Journal article (peer-reviewed)abstract
- In this study we report the synthesis, characterization. and photovoltaic properties of a series of six Conjugated polymers based on donor-acceptor-donor (DAD) structure. The polymers are obtained via Suzuki polymerization of different alkoxy-substituted DAD monomers together with a substituted fluorene or phenylene monomer. Application of polymers as light-harvesting and electron-donating materials in solar cells, in conjunction with both [60]PCBM and [70]PCBM as acceptors, show power-conversion efficiencies (PCEs) up to 2.9%, values obtained without extensive optimization work. Furthermore, atomic force microscopy and field-effect transistor (FET) mobility measurements of acceptor-polymer mixtures show that differences in substitution on the polymers affect morphology, mobility, and device performance. Within the series of polymers, all showing similar optical absorption and redox behavior, substituents play an important role in phase separation on a micrometer scale, which in turn has a large impact on device performance. The phase-separation behavior is clearly seen in [70]PCBM devices where the best-performing devices are obtained using the polymers with short alkoxy groups or no substituents together with a high speed of spin coating during device preparation.
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| 13. |
- Nemec, Hynek, et al.
(author)
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Sub-Picosecond Time-Dependent Mobility in Low-Band-Gap Polyphenylene:Fullerene Blend Probed by Terahertz Spectroscopy
- 2008
-
In: Conference on Lasers and Electro-Optics, 2008 and 2008 Conference on Quantum Electronics and Laser Science. CLEO/QELS 2008. - : IEEE. - 1092-8081. - 9781557528599 ; , s. 3108-3109
-
Conference paper (peer-reviewed)abstract
- Time-resolved terahertz spectroscopy is used to investigate photoinduced dynamics of charge carriers in a polymer heterojunction. We directly observe instantaneous generation of highly mobile charge carriers followed by a rapid drop in their mobility. (C) 2008 Optical Society of America
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| 14. |
- Nemec, Hynek, et al.
(author)
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Ultrafast conductivity in a low-band-gap polyphenylene and fullerene blend studied by terahertz spectroscopy
- 2009
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In: Physical Review B - Condensed Matter and Materials Physics. - 2469-9950 .- 2469-9969 .- 1098-0121. ; 79:24, s. 245326 (art no)-
-
Journal article (peer-reviewed)abstract
- Time-resolved terahertz spectroscopy and Monte Carlo simulations of charge-carrier motion are used to investigate photoinduced transient conductivity in a blend of a low-band-gap polyphenylene copolymer and fullerene derivative. The optical excitation pulse generates free holes delocalized on polymer chains. We show that these holes exhibit a very high initial mobility as their initial excess energy facilitates their transport over defects (potential barriers) on polymer chains. The conductivity then drops down rapidly within 1 ps, and we demonstrate that this decrease occurs essentially by two mechanisms. First, the carriers loose their excess energy and they thus become progressively localized between the on-chain potential barriers-this results in a mobility decay with a rate of (180 fs)(-1). Second, carriers are trapped at defects (potential wells) with a capture rate of (860 fs)(-1). At longer time scales, populations of mobile and trapped holes reach a quasiequilibrium state and further conductivity decrease becomes very slow.
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| 15. |
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| 16. |
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| 17. |
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| 18. |
- Perzon, Erik Per, 1977, et al.
(author)
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An alternating low band-gap polyfluorene for optoelectronic devices
- 2006
-
In: Polymer. ; 47:12, s. 4261-4268
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Journal article (peer-reviewed)abstract
- An alternating polyfluorene (APFO) with low band-gap segments. APFO-Green1, was synthesized for use in optoelectronic devices. The low band-gap segment consists of an electron acceptor (A), fenced by electron donors (D). This D-A-D configuration leads to partial charge transfer in the polymer backbone and a low band-gap of 1.3 eV. Characterization of APFO-Green1 include measurement of light absorption and emission at extended wavelengths and high hole mobility was found. Blends of the polymer with different fullerene derivs. exhibit unusually high photovoltaic performance at long wavelengths, making this type of conjugated polymers promising for application in plastic solar cells. [on SciFinder (R)]
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| 19. |
- Perzon, Erik Per, 1977, et al.
(author)
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Design, Synthesis and Properties of Low Band Gap Polyfluorenes for Photovoltaic Devices
- 2005
-
In: Synthetic Metals. ; 154:1-3, s. 53-56
-
Conference paper (peer-reviewed)abstract
- Two alternating polyfluorene-polythiophene copolymers contg. different low band gap 4,7-di-2-thienyl-2,1,3-benzothiadiazole-5,6-diamine segments were designed and synthesized for use in optoelectronic devices. The low band gap segments consist of electron donating and accepting moieties which induce a partial charge transfer in the polymer backbone and thereby, a lower band gap. The obtained polyfluorenes, APFO-Green1 and APFO-Green2, were studied by measuring optical absorption and emission at extended wavelengths. Blends of the polyfluorenes with fullerene derivs. exhibit unprecedented photovoltaic response at long wavelengths. [on SciFinder (R)]
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| 20. |
- Perzon, Erik Per, 1977
(author)
-
Low Band-Gap Conjugated Polymers for Plastic Solar Cells
- 2007
-
Doctoral thesis (other academic/artistic)abstract
- Today, fossil fuels like coal, oil, and natural gas are used for more than 60% of the world's electricity production. These fuels have a very negative impact on the environment and many researchers agree that the earth's climate is changing as a consequence of fossil fuel emissions. There are several examples of more environmentally friendly ways to produce electricity like bio fuels, hydroelectric power, wind power, and solar energy but for the fossil fuels to be totally replaced, the alternatives must be cost effective, robust, and long lived.Direct conversion of sunlight to electrical energy in solar cells is a very eco-friendly method of generating electricity. Traditional silicon based solar cells have been used in commercial products for a few decades but there are other promising solutions. For instance, polymer based solar cells could be manufactured in cheaper, less complicated, and less energy consuming processes.Design, synthesis, and evaluation of conjugated polymers for solar cells are described. The focus has been on realizing polymers which can absorb light at long wavelengths and convert it into electrical energy. For long wavelength light to be absorbed, the polymer must have a low band-gap which is achieved by introducing so called low band-gap segments. The thesis describes the development of these low band-gap polymers in detail and results from solar cell measurements are given. Unprecedented photovoltaic responses at long wavelengths have been reached and some of the materials presented herein display very promising efficiencies.
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| 21. |
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| 22. |
- Wang, Xiangjun, et al.
(author)
-
Enhanced photocurrent spectral response in low-bandgap polyfluorene and C70-Derivative-Based Solar Cells
- 2005
-
In: Advanced Functional Materials. - : Wiley. - 1616-301X .- 1616-3028. ; 15:10, s. 1665-1670
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Journal article (peer-reviewed)abstract
- Plastic solar cells have been fabricated using a low-bandgap alternating copolymer of fluorene and a donor-acceptor-donor moiety (APFO-Green1), blended with 3-(3,5-bis-trifluoromethylphenyl)-1-(4-nitrophenyl)pyrazolino[70]fullerene (BTPF70) as electron acceptor. The polymer shows optical absorption in two wavelength ranges, < 500 nm and 600 < < 1000 nm. The BTPF70 absorbs light at < 700 nm. A broad photocurrent spectral response in the wavelength range 300 < < 1000 nm is obtained in solar cells. A photocurrent density of 3.4 mA cm-2, open-circuit voltage of 0.58 V, and power-conversion efficiency of 0.7 % are achieved under illumination of AM1.5 (1000 W m-2) from a solar simulator. Synthesis of BTPF70 is presented. Photoluminescence quenching and electrochemical studies are used to discuss photoinduced charge transfer.
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| 23. |
- Wang, Xiangjun, et al.
(author)
-
Enhanced photocurrent spectral response in low-bandgap polyfluorene and C70-derivative-based solar cells
- 2005
-
In: Advanced Functional Materials. ; 15:10, s. 1665-1670
-
Journal article (peer-reviewed)abstract
- Plastic solar cells have been fabricated using a low-bandgap alternating copolymer of fluorene and a donor-acceptor-donor moiety (APFO-Green1), blended with 3'-(3,5-bis-trifluoromethylphenyl)-1'-(4-nitrophenyl)pyrazolino fullerene (BTPF70) as electron acceptor. The polymer shows optical absorption in two wavelength ranges, l
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| 24. |
- Wang, Xiangjun, et al.
(author)
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Polymer solar cells with low-bandgap polymers blended with C70-derivative give photocurrent at 1 μm
- 2006
-
In: Thin Solid Films. - : Elsevier BV. - 0040-6090. ; 511-512, s. 576-580
-
Journal article (peer-reviewed)abstract
- A new series of low-bandgap alternating polyfluorenes with different donor–acceptor–donor moieties have been synthesized. Electrochemical and optical absorption measurement show that onset bandgaps of these polymers range from 1.2 to 1.5 eV. These polymers, blended with a C70-derivative as acceptor, are used for solar cell fabrication. Devices show promising photovoltaic properties, and the spectral response of photocurrent covers all visible and near-infrared wavelength regions with its onset extended to 1 μm. The best data gives a photocurrent density of 3.4 mA/cm2, open circuit voltage of 0.58 V and power conversion efficiency of 0.7% under illumination of AM1.5 (1000 W/m2) from a solar simulator.
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| 25. |
- Zhang, Fengling, et al.
(author)
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High photovoltage achieved in low band gap polymer solar cells by adjusting energy levels of a polymer with the LUMOs of fullerene derivatives
- 2008
-
In: Journal of Materials Chemistry. - : Royal Society of Chemistry (RSC). - 0959-9428 .- 1364-5501. ; 18:45, s. 5468-5474
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Journal article (peer-reviewed)abstract
- Solar cells based on organic molecules or conjugated polymers attract great attention due to their unique advantages, such as low cost, and their use in flexible devices, but are still limited by their low power conversion efficiency (PCE). To improve the PCEs of polymer solar cells, more efforts have been made to increase short-circuit current (J(sc)) or open-circuit voltage (V-oc). However, the trade-off between J(sc) and V-oc in bulk heterojunctions solar cells makes it tricky to find a polymer with a low band gap to efficiently absorb photons in the visible and near infrared region of the solar spectrum, while maintaining a high V-oc in solar cells. Therefore, it is crucial to design and synthesize polymers with energy levels aligning with the LUMO (lowest unoccupied molecular orbital) of an electron acceptor to minimize the LUMO level difference between donor and acceptor to keep enough driving force for charge generation, thereby maximizing photovoltage in solar cells. Here a novel copolymer APFO-Green 9 was synthesized. Polymer solar cells based on APFO-Green 9 blended with a derivative of fullerene demonstrate high photovoltage by fine tuning the HOMO and LUMO level of APFO-Green 9. Solar cells based on APFO-Green 9 and [6,6]-phenyl-C71-butyric acid methyl ester ([70]PCBM) present a photoresponse extended to 900 nm with J(sc) of 6.5 mA cm(-2), V-oc of 0.81 V and PCE of 2.3% under illumination of AM1.5 with light intensity of 100 mW cm(-2). As a low band gap polymer with a V-oc bigger than 0.8 V, APFO-Green 9 is a promising candidate for efficient tandem solar cells.
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| 26. |
- Zhang, Fengling, 1960-, et al.
(author)
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Polymer solar cells based on a low-bandgap fluorene copolymer and a fullerene derivative with photocurrent extended to 850 nm
- 2005
-
In: Advanced Functional Materials. - : Wiley. - 1616-3028 .- 1616-301X. ; 15:5, s. 745-750
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Journal article (peer-reviewed)abstract
- Polymer solar cells were fabricated from a low band-gap alternating polyfluorene copolymer, APFO-Green2, combined with [6,6]-phenyl-C61-butyric acid Me ester (PCBM), from org. solns. External quantum efficiencies of the solar cells show an onset at 850 nm and a peak of >10% located at 650 nm, which corresponds to the extended absorption spectrum of the polymer. A photocurrent of 3.0 mA/cm2, photovoltage of 0.78 V, and power conversion efficiency of 0.9% were obtained with solar cells based on this new low-bandgap polymer under an illumination of AM 1.5 (1000 W/m2) from a solar simulator. [on SciFinder (R)]
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