Abstract

Organic Light Emitting Device (OLED) has been a promising new research area that has received a lot of attention in the recent. It is very important to improve lifetime and efficiency of OLED using a new technique. It is well known that an OLED is basically a p-n junction where the p and n layers are made of organic semiconductors. With forward bias, the holes injected from the p-layer and the electrons injected from the n-layer pair up to form excitons near the junction (assume, for simplicity of discussion, that the probability for this process is unity). An exciton can be either a triplet (spin S=1) or a singlet (spin S=0), depending on the spins of the holes and electrons. For most organic emitter, the singlet exciton decays radiatively and rapidly, emitting a photon but the triplet exciton decays non-radiatively and relatively slowly, emitting phonons (heat) rather than photons (light). Thus, the relative population of triplet and singlet excitons determines the internal quantum efficiency of the OLED. For unpolarized carrier injection, the probability of forming a triplet is 75 %. Therefore at least 75% of electron-hole recombination events are wasted in heat, and the maximum internal quantum efficiency is limited to meager 25 %. This situation can be changed if spin polarized holes and electrons are injected in the OLED. It would then be possible to preferentially form triplets or singlets by controlling the spin polarizations of the injected carriers. In this paper, We fabricated OLED using spin LSMO substrate. The structure is LSMO/NPB/Alq3/CsF/Mg:Ag. The characteristic brightness, voltage and current of these devices were investigated in the magnetic field. The photovoltaic character was little affected by the magnetic field in the device using LSMO substrate. This phenomenon was related on the ratio of single exciton and triplet exciton in the emissive layer.

© 2015 Optical Society of America

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