The role played by cell configuration and layer preparation in LEDs based on hydroxyquinoline metal complexes and a triphenyl-diamine derivative (TPD)

We have constructed and characterized organic light emitting diodes (OLEDs) based on the combination of active materials belonging to the triphenyldiamine family N,N′-diphenyl-N,N′-bis(3-methylphenyl)-[1.1′ biphenyl]-4,4′ diamine (TPD) with metal complexes of hydroxyquinoline such as (8-hydroxyquinolinate)-Al(III) [Alq3] and Zn(II) [Znq2]. The OLEDs, fabricated by different techniques, both in single (SL) and double-layer configurations (DL), showed, under steady-state driving voltage, meaningful improvements in operating voltage and luminance tuning from SL to DL. Luminance of about 10000 cd/m2 was achieved for cells constructed in double-layer configuration, when one layer contains a mixture of polycarbonate and TPD, prepared by spinning technique.