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Title: The use of charge extraction by linearly increasing voltage in polar organic light-emitting diodes
Authors : Züfle, Simon
Altazin, Stéphane
Hofmann, Alexander
Jäger, Lars
Neukom, Martin
Schmidt, Tobias D.
Brütting, Wolfgang
Ruhstaller, Beat
Published in : Journal of Applied Physics
Volume(Issue) : 121
Issue : 175501
Publisher / Ed. Institution : A I P Publishing LLC
Issue Date: May-2017
License (according to publishing contract) : CC BY 3.0: Namensnennung 3.0 Unported
Type of review: Peer review (Publication)
Language : English
Subject (DDC) : 621.3: Electrical engineering and electronics
Abstract: We demonstrate the application of the CELIV (charge carrier extraction by linearly increasing voltage) technique to bilayer organic light-emitting devices (OLEDs) in order to selectively determine the hole mobility in N,N0-bis(1-naphthyl)-N,N0-diphenyl-1,10-biphenyl-4,40-diamine (α-NPD). In the CELIV technique, mobile charges in the active layer are extracted by applying a negative voltage ramp, leading to a peak superimposed to the measured displacement current whose temporal position is related to the charge carrier mobility. In fully operating devices, however, bipolar carrier transport and recombination complicate the analysis of CELIV transients as well as the assignment of the extracted mobility value to one charge carrier species. This has motivated a new approach of fabricating dedicated metal-insulator-semiconductor (MIS) devices, where the extraction current contains signatures of only one charge carrier type. In this work, we show that the MIS-CELIV concept can be employed in bilayer polar OLEDs as well, which are easy to fabricate using most common electron transport layers (ETLs), like Tris-(8-hydroxyquinoline)aluminum (Alq3). Due to the macroscopic polarization of the ETL, holes are already injected into the hole transport layer below the built-in voltage and accumulate at the internal interface with the ETL. This way, by a standard CELIV experiment only holes will be extracted, allowing us to determine their mobility. The approach can be established as a powerful way of selectively measuring charge mobilities in new materials in a standard device configuration.
Departement: School of Engineering
Organisational Unit: Institute of Computational Physics (ICP)
Publication type: Article in scientific Journal
DOI : 10.1063/1.4982903
ISSN: 0021-8979
Appears in Collections:Publikationen School of Engineering

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