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Eindhoven, Netherlands

Nicolai H.T.,Zernike Institute for Advanced Materials | Hof A.,Zernike Institute for Advanced Materials | Blom P.W.M.,Zernike Institute for Advanced Materials | Blom P.W.M.,Holst Center
Advanced Functional Materials | Year: 2012

The charge transport and recombination in white-emitting polymer light- emitting diodes (PLEDs) are studied. The PLED investigated has a single emissive layer consisting of a copolymer in which a green and red dye are incorporated in a blue backbone. From single-carrier devices the effect of the green- and red-emitting dyes on the hole and electron transport is determined. The red dye acts as a deep electron trap thereby strongly reducing the electron transport. By incorporating trap-assisted recombination for the red emission and bimolecular Langevin recombination for the blue emission, the current and light output of the white PLED can be consistently described. The color shift of single-layer white-emitting PLEDs can be explained by the different voltage dependencies of trap-assisted and bimolecular recombination. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.


Kotlarki J.D.,Zernike Institute for Advanced Materials | Blom P.W.M.,Zernike Institute for Advanced Materials | Blom P.W.M.,Holst Center
Applied Physics Letters | Year: 2012

In a normal solar cell, most charge carriers are generated close to the anode, such that electrons have to travel a longer distance as compared to the holes. In an inverted solar cell, holes have to travel a longer distance. We use a combined optical and electronic model to simulate the effect of unbalanced transport on the efficiency of normal and inverted single and tandem solar cells. When the electrons are ten times more mobile than the holes, the efficiency for a single cell with a thickness of 250 nm drops from 7.5% to 4.5% when changing from a normal to an inverted structure. For opposite mobility ratio, the inverted structure clearly outperforms the normal structure. © 2012 American Institute of Physics.


Gelinck G.,Holst Center | Heremans P.,IMEC | Heremans P.,Catholic University of Leuven | Nomoto K.,Sony Corporation | Anthopoulos T.D.,Imperial College London
Advanced Materials | Year: 2010

Organic thin-film transistors (OTFTs) offer unprecedented opportunities for implementation in a broad range of technological applications spanning from large-volume microelectronics and optical displays to chemical and biological sensors. In this Progress Report, we review the application of organic transistors in the fields of flexible optical displays and microelectronics. The advantages associated with the use of OTFT technology are discussed with primary emphasis on the latest developments in the area of active-matrix electrophoretic and organic light-emitting diode displays based on OTFT backplanes and on the application of organic transistors in microelectronics including digital and analog circuits. © 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.


Zhang Y.,Zernike Institute for Advanced Materials | Blom P.W.M.,Zernike Institute for Advanced Materials | Blom P.W.M.,Holst Center
Applied Physics Letters | Year: 2011

We investigate the electron and hole transport in poly[(9,9-di-n- octylfluorenyl-2,7-diyl)-alt-(benzo[2,1,3]thiadiazol-4,8-diyl)] (F8BT). An Ohmic hole contact on F8BT is achieved by using the high work function anode MoO 3 as hole injection contact, enabling the occurrence of space-charge limited currents. The electron transport in F8BT is trap-limited and the traps can be deactivated using n -type doping by decamethylcobaltocene (DMC). Due to the alignment of the energy levels of DMC and F8BT the electrons from the DMC donor not only fill the traps but also fill up the lowest unoccupied molecular orbital of F8BT such that the electron transport can be enhanced beyond the hole transport. © 2011 American Institute of Physics.


Kuik M.,Zernike Institute for Advanced Materials | Koster L.J.A.,Zernike Institute for Advanced Materials | Wetzelaer G.A.H.,Zernike Institute for Advanced Materials | Blom P.W.M.,Zernike Institute for Advanced Materials | Blom P.W.M.,Holst Center
Physical Review Letters | Year: 2011

The trap-assisted recombination of electrons and holes in organic semiconductors is investigated. The extracted capture coefficients of the trap-assisted recombination process are thermally activated with an identical activation energy as measured for the hole mobility μ p. We demonstrate that the rate limiting step for this mechanism is the diffusion of free holes towards trapped electrons in their mutual Coulomb field, with the capture coefficient given by (q/ε)μ p. As a result, both the bimolecular and trap-assisted recombination processes in organic semiconductors are governed by the charge carrier mobilities, allowing predictive modeling of organic light-emitting diodes. © 2011 American Physical Society.

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