Abstract
We fabricate the phenyl-substituted poly(p-phenylene vinylene) copolymer (super yellow, SY-PPV)-based polymer light-emitting diodes (PLEDs) with different device architectures to modulate the injection of opposite charge carriers and investigate the corresponding magnetoconductance (MC) responses. At the first glance, we find that all PLEDs exhibit the positive MC responses. By applying the mathematical analysis to fit the curves with two empirical equations of a non-Lorentzian and a Lorentzian function, we are able to extract the hidden negative MC component from the positive MC curve. We attribute the growth of the negative MC component to the reduced interaction of the triplet excitons with charges to generate the free charge carriers as modulated by the applied magnetic field, known as the triplet exciton-charge reaction, by analyzing MC responses for PLEDs of the charge-unbalanced and hole-blocking device configurations. The negative MC component causes the broadening of the line shape in MC curves.
Highlights
Organic spintronics, a research field that studies the electrical, optical and magnetic behaviors of advanced spintronic devices using organic semiconductor,[1,2,3] has attracted much attention in the past few decades owing to its long spin lifetimes,[4] ease of fabrication and preparation processes, and the low cost for the device fabrication.[5]
The results suggest that the increasing negative MC component broadens the line shape of MC curves, in which the modulation of triplet exciton-charge reaction within SY-PPV layer in polymer light-emitting diodes (PLEDs) can be characterized by analyzing MC responses for devices of the balanced, unbalanced, and hole-blocking injection of charge carriers
The above observations agree well with the proposed model that the dissociation of electron-hole pairs under the applied magnetic field contributes to the positive MC response.[22]
Summary
A research field that studies the electrical, optical and magnetic behaviors of advanced spintronic devices using organic semiconductor,[1,2,3] has attracted much attention in the past few decades owing to its long spin lifetimes,[4] ease of fabrication and preparation processes, and the low cost for the device fabrication.[5]. The positive MC response is attributed to the change of the spin sublevels mixing via the hyperfine interaction in electrostatically bound electron-hole polaron pairs by the magnetic field and the negative MC component is caused by the change in spin mixing of electron and hole bipolarons.[6] Bloom et al.[18] demonstrated the change of MC sign from negative MC to positive MC response as the increase of applied bias voltage in poly(2-methoxy-5-(3’,7’-dimethyloctyloxy)-p-phenylene vinylene)-based PLED They attributed the change of the sign for MC responses to the transition from unipolar to bipolar charge transport in the device. The results suggest that the increasing negative MC component broadens the line shape of MC curves, in which the modulation of triplet exciton-charge reaction within SY-PPV layer in PLEDs can be characterized by analyzing MC responses for devices of the balanced, unbalanced, and hole-blocking injection of charge carriers
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