Poor confinement of e-h recombination zone in blue oleds

The possibility of making large light-emitting area with low cost has stimulated the research work on organic-based light-emitting devices (OLEDs). OLEDs with emission color covering almost the entire visible range have been realized. This was achieved by simultaneously synthesizing new materials and optimizing the device structure itself by adding/getting rid of different layers. Recently, OLEDs performance has improved and has become adequate for many display applications. However, the main problem still to be solved, concerns the short lifetime of the devices. Surprisingly, there are only few fundamental works on the degradation mechanisms of OLEDs. The mechanisms behind the light decay and the color shifts, especially for blue colour, are still not fully understood. Earlier studies have suggested that the poor balance between the number of electrons and holes in the emitting layer, is one of the main factors in limiting the lifetime of the device.