| 61. |
- Berggren, Magnus, et al.
(författare)
-
Controlling colour by voltage in polymer light emitting diodes
- 1995
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Ingår i: Synthetic metals. - : Elsevier. - 0379-6779 .- 1879-3290. ; 71:1-3, s. 2185-2186
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Tidskriftsartikel (refereegranskat)abstract
- We report electroluminescence using different substituted polythiophenes as the emitting mterial. Different substituents cause different sterical interacion which force the thiophene rings out of planarity. This results in different bandgaps. Colours from blue to near infrared have been demonstrated in electroluminescent devices. We also demonstrate voltage controlled electroluminescence using mixtures of these polymers.
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| 62. |
- Berggren, Magnus, et al.
(författare)
-
Controlling inter-chain and intra-chain excitations of a poly(thiophene) derivative in thin films
- 1999
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Ingår i: Chemical Physics Letters. - : Elsevier. - 0009-2614 .- 1873-4448. ; 304:1-2, s. 84-90
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Tidskriftsartikel (refereegranskat)abstract
- The decay of photoexcitations in polythiophene chains has been studied in solid solutions of the polymer from room temperature to 4 K. A strong blue shift of the emission spectrum is observed in the polymer blend, as compared to the homopolymer. Dispersion of the polythiophene suppresses the non-radiative processes, which are suggested to be correlated to close contacts of polymer chains. Quantum chemistry modeling of the excited state distributed on two chains corroborate this conclusion.
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| 63. |
- Berggren, Magnus, et al.
(författare)
-
Green Electroluminescence in Poly-(3-cyclohexylthiophene) light-emitting diodes
- 1994
-
Ingår i: Advanced Materials. - : Wiley-VCH Verlag Berlin. - 0935-9648 .- 1521-4095. ; 6:6, s. 488-490
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Tidskriftsartikel (refereegranskat)abstract
- Electoluminescent devices based on polythiophene-system this films have been demonstrated that together span the entire visible range, steric hindrance being used to vary the bandgap between compunds. Poly-(3-cyclohexylthiophene), see Figures, exhibits green electoluminescence. Possible interpretations of this observation are proposed.
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| 64. |
- Berggren, Magnus, et al.
(författare)
-
Light-emitting diodes with variable colours from polymer blends
- 1994
-
Ingår i: Nature. - : Nature Publishing Group. - 0028-0836 .- 1476-4687. ; 372:6505, s. 444-446
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Tidskriftsartikel (refereegranskat)abstract
- THE range of materials now available for polymer-based light-emitting diodes (LEDs) is such that electroluminescence can be obtained throughout the visible spectrum(1-12). Here we show that, by blending polymers with different emission and charge-transport characteristics, LEDs can be fabricated in which the emission colour varies as a function of the operating voltage. This phenomenon arises from the self-organizing properties of the blends, in which entropy drives phase separation of the constituent polymers and gives rise to submicrometre-sized domains having a range of compositions and emission characteristics. Emission from domains of different composition is controlled by the ease with which charge is injected, which in turn depends on the applied voltage.
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| 65. |
- Berggren, Magnus, et al.
(författare)
-
Polymer light-emitting diodes placed in microcavities
- 1996
-
Ingår i: Synthetic metals. - : Elsevier. - 0379-6779 .- 1879-3290. ; 76:1-3, s. 121-123
-
Tidskriftsartikel (refereegranskat)abstract
- The use of resonant optical microcavities to influence the emission properties of conjugated polymer light-emitting diodes (LEDs) is reported. The microcavities, which are built using metallic mirrors and polymeric spacers, incorporate polymer LEDs in between the mirrors. We report experimental results of polymer LEDs based on substituted polythiophenes. The effects include substantial narrowing of the spectral width of the emitted light, enhancement of the emission at the microcavity resonance, and coupling of two emission processes to different resonance modes in the same cavity.
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| 66. |
- Berggren, Magnus, et al.
(författare)
-
Thermal control of near‐infrared and visible electroluminescence in alkyl‐phenyl substituted polythiophenes
- 1994
-
Ingår i: Applied Physics Letters. - : American Institute of Physics (AIP). - 0003-6951 .- 1077-3118. ; 65:12, s. 1489-1491
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Tidskriftsartikel (refereegranskat)abstract
- We report electroluminescence from a regioregular alkyl-phenyl substituted polythiophene. The polymer film exists in two forms, giving widely different optical absorption, as well as photoluminescence and electroluminescence spectra. In the low-bandgap form, we observe high emission intensity centered at 1.55 eV (800 nm), well into the infrared, while the high-bandgap form gives a maximum at 1.85 eV (670 nm). The conversion from the high-bandgap form to the low-bandgap form can be done by thermal treatment of the polymer light emitting diodes.
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| 67. |
- Berggren, Magnus, et al.
(författare)
-
Ultraviolet electroluminescence from an organic light emitting diode
- 1995
-
Ingår i: Advanced Materials. - : Wiley-VCH Verlag Berlin. - 0935-9648 .- 1521-4095. ; 7:11, s. 900-903
-
Tidskriftsartikel (refereegranskat)abstract
- The extension of the emission region for organic LEDs into the ultraviolet region is reported. Emission at 394 nm is achieved by modifying the geometry of a device based on poly(octylphenyl)bithiophene (PTOPT) and poly(octylphenyl)oxadiazole (PBD) which had previously been shown to emit white light. Through changing the geometry the red and green emission peaks have been suppressed and the UV band (from the PBD) enhanced.
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| 68. |
- Berggren, Magnus, et al.
(författare)
-
White light from an electroluminescent diode made from poly[3(4‐octylphenyl)‐2,2′‐bithiophene] and an oxadiazole derivative
- 1994
-
Ingår i: Journal of Applied Physics. - : American Institute of Physics (AIP). - 0021-8979 .- 1089-7550. ; 76:11, s. 7530-7534
-
Tidskriftsartikel (refereegranskat)abstract
- We report on an electroluminescent diode emitting red, green, and blue light simultaneously. The device is based on a thin polymer layer, poly[3‐(4‐octylphenyl)‐2,2′‐bithiophene] and a thick molecular layer, 2‐(4‐biphenylyl)‐5‐(4‐tertbutyl‐phenyl)1,3,5‐oxadiazole. The quantum efficiency for light conversion is 0.3% and the turn‐on voltage for light emission is 7 V. In this article we present electric and spectroscopic characterizations. A mechanism for the light emission, based on electron and hole recombination between the two organic layers, is proposed
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| 69. |
- Bergqvist, Jonas, et al.
(författare)
-
Asymmetric photocurrent extraction in semitransparent laminated flexible organic solar cells
- 2018
-
Ingår i: npj Flexible Electronics. - : Springer Science and Business Media LLC. - 2397-4621. ; 2:1
-
Tidskriftsartikel (refereegranskat)abstract
- Scalable production methods and low-cost materials with low embodied energy are key to success for organic solar cells. PEDOT(PSS) electrodes meet these criteria and allow for low-cost and all solution-processed solar cells. However, such devices are prone to shunting. In this work we introduce a roll-to-roll lamination method to construct semitransparent solar cells with a PEDOT(PSS) anode and an polyethyleneimine (PEI) modified PEDOT(PSS) cathode. We use the polymer:PCBM active layer coated on the electrodes as the lamination adhesive. Our lamination method efficiently eliminates any shunting. Extended exposure to ambient degrades the laminated devices, which manifests in a significantly reduced photocurrent extraction when the device is illuminated through the anode, despite the fact that the PEDOT(PSS) electrodes are optically equivalent. We show that degradation-induced electron traps lead to increased trap-assisted recombination at the anode side of the device. By limiting the exposure time to ambient during production, degradation is significantly reduced. We show that lamination using the active layer as the adhesive can result in device performance equal to that of conventional sequential coating.
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| 70. |
- Bergqvist, Jonas, et al.
(författare)
-
Determination of optical constants and phase transition temperatures in polymer fullerene thin films for polymer solar cells
- 2012
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Plastic photovoltaics combining semiconducting polymers with fullerene derivatives have the potentialto become the first cost efficient solar cells able to compete with fossil fuels. The maximum powerconversion efficiency is already 8.3%[1] , and new polymers arrive frequently in the search for efficienciesof 10%. As a first step in the screening of candidate materials, the optical constants of the purepolymer as well as the polymer blend with fullerenes are determined from Variable Angle SpectroscopicEllipsometry (VASE), using Tauc-Lorentz oscillator models, throughout the solar spectrum. Thesemodels are then used to predict the upper limits to photocurrent generation in devices, in transfermatrix simulations of the multilayer thin film photovoltaic devices. This forms an essential step in thechoice of materials for optimization in devices.Materials optics measurements are also used to deduce the phase diagram of polymer and polymerblend films. The glass transition temperature is very important for plastic solar cells and mustbe higher than the 80C a device can reach to avoid degradation during operation. Temperaturedependent ellipsometric measurements has proven to be a feasible way to determine phase transitionsin polymer thin films[2] . These transitions are displayed as a sudden change of the volumetricexpansion coefficient, and are manifested by an abrupt increase of thickness at the phase transitiontemperature. For thickness determination a Cauchy model is applied to the transparent infrared partof the spectra.References1. Z. He, C. Zhong, X. Huang, W-Y. Wong, H. Wu, L. Chen, S. Su, Y Cao, Advanced Materials 23, 4636(2011)2. M. Campoy-Quiles, P.G. Etchegoin, D.D.C. Bradley, Synthetic Metals 155, 279(2005)
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