Organic light-emitting diode having doped layers

An organic light emitting diode, comprising:

• a first conductor being an anode;
• a first p-doped semiconductor organic layer in electrical contact with the first conductor and doped with a first dopant having a LUMO level positioned below the HOMO level of the host material of this semiconductor organic layer;
• an electroluminescent layer over the first p-doped semiconductor organic layer;
• a second n-doped semiconductor organic layer over the electroluminescent layer and doped with a second dopant having an HOMO level positioned above the LUMO level of the host material of this semiconductor organic layer;
• and
• a second conductor being a cathode in electrical contact with the second doped organic layer;
• wherein one of the first and second doped semiconductor organic layers having the corresponding first p-dopant or second n-dopant comprises a dopant gradient that is increasing from a lower level in a layer of the doped semiconductor organic layer closer to the electroluminescent layer, to a higher level in a layer of the doped semiconductor organic layer closer to the corresponding first or second conductor;
• and wherein the gradient causes an average conductivity of the doped semiconductor organic layer with said gradient at least three times higher at its interface with the first or second conductor than in a core of this doped organic layer;
• thereby allowing both charge injection and transport of a first or second charge type corresponding to the first or second conductivity types in the first or second doped semiconductor organic layers, such that luminosity of the diode is increased for a given voltage.