* Astronomy

Electron and hole modulating electrodes in organic light emitting diodes
Certain organic thin films emit light under the action of electric field. If such organic thin film whose thickness is of the order of wavelength of light is sandwiched between a cathode and an anode and applied with a voltage in the range of 57 V, substantial amount of light can be generated. Organic light emitting diodes (OLED) are fabricated exploiting this phenomenon of light emission, usually called Electro-luminescence. The basic mechanism, by which the light emission takes place in an organic layer, is through the recombination of electrons and holes in the organic layer. The electrons come in to the organic layer from the cathode that emits and injects electrons in to the organic layer with the help of externally applied electricfield. Similarly holes come in to the organic layer from the anode which injects holes in to the organic layer under the action of externally applied electric field. On either side of the organic layer, that emits light, there are other organic layers that transport electrons from the cathode and holes from the anode. For efficient operation of OLED, all the electrons and holes that reach the emissive organic layer should recombine to produce light. Holes need to go up to the emissive organic layer and not beyond. Similarly electrons need to go up to the emissive organic layer and not beyond. Electrons and holes going beyond the emissive organic layer are considered to be a loss because they do not take part in recombination and subsequent emission of light.

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