Magnetic field effect in organic films and devices

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Title Magnetic field effect in organic films and devices
Publication Type dissertation
School or College College of Science
Department Physics & Astronomy
Author Gautam, Bhoj Raj
Date 2013-08
Description In this work, we focused on the magnetic field effect in organic films and devices, including organic light emitting diodes (OLEDs) and organic photovoltaic (OPV) cells. We measured magnetic field effect (MFE) such as magnetoconductance (MC) and magneto-electroluminescence (MEL) in OLEDs based on several π-conjugated polymers and small molecules for fields B<100 mT. We found that both MC(B) and MEL(B) responses in bipolar devices and MC(B) response in unipolar devices are composed of two B-regions: (i) an ‘ultra-small' region at |B| < 1-2 mT, and (ii) a monotonic response region at |B| >∼2mT. Magnetic field effect (MFE) measured on three isotopes of Poly (dioctyloxy) phenylenevinylene (DOO-PPV) showed that both regular and ultra-small effects are isotope dependent. This indicates that MFE response in OLED is mainly due to the hyperfine interaction (HFI). We also performed spectroscopy of the MFE including magneto-photoinduced absorption (MPA) and magneto-photoluminescence (MPL) at steady state conditions in several systems. This includes pristine Poly[2-methoxy-5-(2-ethylhexyl-oxy)-1,4-phenylene-vinylene] (MEH-PPV) films, MEH-PPV films subjected to prolonged illumination, and MEH-PPV/[6,6]-Phenyl C61 butyric acid methyl ester (PCBM) blend, as well as annealed and pristine C60 thin films. For comparison, we also measured MC and MEL in organic diodes based on the same materials. By directly comparing the MPA and MPL responses in films to MC and MEL in organic diodes based on the same active layers, we are able to relate the MFE in organic diodes to the spin densities of the excitations formed in the device, regardless of whether they are formed by photon absorption or carrier injection from the electrodes. We also studied magneto-photocurrent (MPC) and power conversion efficiency (PCE) of a 'standard' Poly (3-hexylthiophene)/PCBM device at various Galvinoxyl radical wt%. We found that the MPC reduction with Galvinoxyl wt% follows the same trend as that of the PCE enhancement. In addition, we also measured the MPC response of a series of OPV cells. We attribute the observed broad MPC to short-lived charge transfer complex species, where spin mixing is caused by the difference, Δg of the donor/acceptor g factors; whereas narrow MPC is due to HFI within long-lived polaron-pairs.
Type Text
Publisher University of Utah
Subject Electroluminescence; Hyperfine; Magneto-resistance; Photocurrent; Photoinduced absorption; Polaron pair
Dissertation Institution University of Utah
Dissertation Name Doctor of Philosophy
Language eng
Rights Management Copyright © Bhoj Raj Gautam 2013
Format application/pdf
Format Medium application/pdf
Format Extent 2,257,211 bytes
Identifier etd3/id/2517
ARK ark:/87278/s6fb8b22
Setname ir_etd
ID 196093
Reference URL https://collections.lib.utah.edu/ark:/87278/s6fb8b22
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