Organic light emitting diodes

Conjugated polymers are presently being used extensively for the fabrication of light emitting diodes. Some of the materials, which found application for these devices, are Alq(3), PPV and its derivatives. The main drawbacks, which are preventing the commercialization of, conjugated polymer based light emitting diodes, are their low quantum efficiency similar to0.1% and fast degradation. The main problems which are to be tackled in this area are: (a) The mobility of electron as well as concentration of the injected electron is lower than the mobility and concentration of injected holes. (b) Exciton formation in the conjugated polymer is very predominant and the recombinations due to free carriers are insignificant, resulting in low recombination probability. In the present work, Alq(3)[tri(8-hydroxyquinaline)aluminium] has been used as emissive layer for device fabrication. Three types of structures namely hole- only (ITO/ Alq(3)/Au), electron-only (Al/ Alq(3)/Al), and bipolar (ITO/ Alq(3)/Al) were fabricated and their I-V characteristics were studied. It was found that quantum mechanical tunneling dominates the charge transport in all the above three devices. The study on PPV and mobility measurements by time of flight method are in progress.