| 361. |
- Persson, Nils-Krister, 1966-, et al.
(författare)
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Optical optimization of polyfluorene-fullerene blend photodiodes
- 2005
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 97:3, s. 034503-1-034503-8
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Tidskriftsartikel (refereegranskat)abstract
- Blends of polyfluorene-fullerenes are promising materials for polymer-based photovoltaic devices (PPVD). Using spectroscopic ellipsometry we deduce the dielectric function for the blend of the fullerene derivative [6,6]-phenyl-C 61-butyric acid methyl ester (PCBM) and the alternating polyfluorene copolymer, poly [2,7-(9,9-dioctyl-fluorene)-alt-5,5-(4',7'-di-2-thienyl-2',1', 3'-benzothiadiazole)] DiO-PFDTBT (4:1 by weight), for the wavelength interval 250-1300 nm. n reaches above 2 and saturates to 1.9 for high wavelengths. Absorption starts at 720 nm (1.72 eV) and reaches a crest around 550 nm (2.25 eV). The spin coating introduces anisotropy in the blend, manifested in birefringence as well as in dichroism. The dielectric function for the blend versus its constituents is not additive. There are indications that the constituents lost their dielectric identity, as screening cannot explain the experimental data. Simulations of optical absorption inside a PPVD are performed for both monochromatic and polychromatic light, using an air mass 1.5 distributed solar irradiation. The model allows calculation of absorbed energies in absolute values in all layers within the device. An optimization is carried out with respect to the layer thicknesses. From a purely optical perspective there is no gain of optical absorbance in including an additional layer of acceptor. Spatially resolved energy dissipation within the device is presented for polychromatic light. Estimates for quantum efficiencies are derived. Experimental and theoretical results for reflectance are compared.
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| 362. |
- Persson, Nils-Krister, et al.
(författare)
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Optical properties of low band gap alternating copolyfluorenes for photovoltaic devices
- 2005
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 123:20, s. 204718-
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Tidskriftsartikel (refereegranskat)abstract
- In a joint experimental and theoretical work the optical response and excited-state character of two novel conjugated polymers for photovoltaic applications are studied. The polymers, alternating polyfluorene (APFO) Green 1 and APFO Green 2, are both copolymers of fluorene, thiophene, and electron accepting groups. The band gaps are extended into the red and near infrared with onsets of 780 and 1000 nm, respectively, due to alternating donor and acceptor moieties along the polymer chain. Spectroscopic ellipsometry and subsequent modeling made it possible to extract the dielectric function in the range of 260-1200 nm. Semiempirical quantum chemical calculations (ZINDO) revealed the character of the main electronic transitions in the studied spectral region. The spectral band just above 400 nm was assigned to a delocalized π - π* transition for both polymers. The red band lying at 622 and 767 nm in the two polymers corresponds to an electronic state mainly occupying the acceptor units and having a strong charge-transfer character. We show that the ZINDO transition energies are valuable input to the application of Lorentz oscillators in modeling of the dielectric function of the polymer material.
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| 363. |
- Persson, Nils-Krister, 1966-, et al.
(författare)
-
Organic tandem solar cells - modelling and predictions
- 2006
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Ingår i: Solar Energy Materials and Solar Cells. - : Elsevier BV. - 0927-0248 .- 1879-3398. ; 90:20, s. 3491-3507
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Tidskriftsartikel (refereegranskat)abstract
- Tandem combinations of organic photovoltaic devices are studied from an optical point of view. We unify coherent (wave-based) as well as incoherent (irradiance-based) light addition in our treatment of the incoming and reflected electromagnetic waves, and calculate the spatially resolved absorption profile in the cells. The model allows for any number and any order of thin and thick layers to be analysed. Irradiation is monochromatic or polychromatic, AM 1.5 or AM 1.0, and therefore applicable for solar cell simulation. The optical modelling is unified with electrical models of charge generation and transport in the solar cells. Through this, de-coupling of optical and electrical processes is possible. Moreover, the model allows identification of limiting processes in the devices. The model is applied to a tandem cell with copolymers of polyfluorene combined in bulk heterojunctions with fullerene acceptors, one device for high energy absorption and one for lower, where anodes and cathodes for the cells are semi-transparent metallic polymer layers. It is concluded that these materials do not at present have an electrical performance, which can be enhanced by the tandem cell combination.
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| 364. |
- Persson, Nils-Krister, 1966-, et al.
(författare)
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Simulations of optical processes in organic photovoltaic devices
- 2005. - 1
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Ingår i: Organic Photovoltaics. - Boca Raton, FL, USA : CRC Press. - 082475963X - 9780824759636 ; , s. 107-138
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Bokkapitel (övrigt vetenskapligt/konstnärligt)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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| 365. |
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| 366. |
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| 367. |
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| 368. |
- Pettersson, Fredrik, et al.
(författare)
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Surface micromachined polymer actuators as valves in PDMS microfluidic system
- 2000
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Ingår i: 1st Annual International, Conference On Microtechnologies in Medicine and Biology. 2000. - : IEEE. - 0780366034 ; , s. 334-335
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Konferensbidrag (refereegranskat)abstract
- To control flows in microfluidic systems there is a need of valves. Desirable properties of such valves are in general low cost, low dead-volume, fast response and low power-consumption. For bioanalytical purposes the requirements also include biocompatibility and ability to function in biological fluids. One way to address these problems is to use surface-fabricated actuators, and then bonding the actuator chip with high aspect-ratio flow-channels in a thick polymer cover. A suitable cover structure can be made in elastomeric poly(dimethylsiloxane) (PDMS) which can be joined to a silicon surface. The active valve structures can be micromuscles, i.e. actuators based on conjugated polymer such as polypyrrole (PPy), which can be electrochemically doped. The reversible doping of PPy forces counterions to flow into or out of the polymer to balance the charge, resulting in a volume change. This volume change can be used in a bilayer actuator, where a metal can serve as constant volume layer as well as electrical contact to the polymer layer changing volume under reversible doping
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| 369. |
- Pettersson, Lars, et al.
(författare)
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Optical anisotropy in thin films of poly(3,4-ethylenedioxythiophene)- poly(4-styrenesulfonate)
- 2002
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Ingår i: Organic electronics. - 1566-1199 .- 1878-5530. ; 3:3-4, s. 143-148
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Tidskriftsartikel (refereegranskat)abstract
- Anisotropic optical constants spectrum of spin-coated thin films of poly(3,4-ethylenedioxythiophene)-poly(4-styrenesulfonate) (PEDOT-PSS) from 200 to 1700 nm were determined using variable-angle spectroscopic ellipsometry and polarized intensity transmission data together with absorption spectroscopy. PEDOT-PSS was found to be very anisotropic, uniaxial with the optic axis parallel to the surface normal. The result is in good agreement with results obtained of chemically polymerized PEDOT layers doped with toluenesulfonate. By adding sorbitol to the PEDOT-PSS dispersion before spin-coating, layers with a higher conductivity were obtained. A detailed study was made of the optical response of these layers in comparison to the PEDOT-PSS prepared from dispersions without sorbitol. The optical anisotropy is important to consider when using PEDOT-PSS in optoelectronic devices, such as polymer light-emitting diodes and photovoltaic devices. © 2002 Elsevier Science B.V. All rights reserved.
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| 370. |
- Pettersson, Lars, et al.
(författare)
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Quantum efficiency of exciton-to-charge generation in organic photovoltaic devices
- 2001
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 89:10, s. 5564-5569
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Tidskriftsartikel (refereegranskat)abstract
- We present an analysis of the internal monochromatic quantum efficiency of photovoltaic devices based on polymer and polymer/fullerene thin films. A quantum efficiency of exciton-to-charge generation is defined as the external monochromatic quantum efficiency normalized to the absorption in the active materials of the device. An upper limit of the efficiency can be determined, and results show that much of the light is absorbed in photoactive layers of the device, whereas only a fraction of the generated excitons is converted to charge carriers and can be collected as photocurrent. © 2001 American Institute of Physics.
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