Efficient multilayer organic light emitting diode

Some organic light emitting diodes with Alq(3) as emission layer, multilaye r composed of m-MTDATA, NPB, TPD or SA as hole transport layer and lithium doped Alq(3) as electron injection assistant layer have been investigated. The current voltage characteristics and the electroluminescent (EL) output voltage characteristics have been investigated. It is found that the m-MTDA TA is suitable as a hole injection layer close to the hole injection electr ode ITO, NPB is suitable in contact with the emission layer, SA and TPD can be inserted between them to form an energy ladder structure, with which th e efficiency of device has been increased. When thin Lithium doped Alq(3) l ayer is inserted between Alq(3) and the aluminium electrode, the driving vo ltage of the devices has been clearly decreased while the current density a nd the EL output increased. (C) 2001 Elsevier Science B.V. All rights reser ved.