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 triphenyldia mine family N,N'-diphenyl-N,N'-bis(3-methylphenyl)-[1.1'biphenyl]-4,4'diami ne (TPD) with metal complexes of hydroxyquinoline such as (8-hydroxyquinoli nate)-Al(III) [Alq(3)] and Zn(II) [Znq(2)]. The OLEDs,fabricated by differe nt techniques, both in single (SL) and double-layer configurations (DL), sh owed, under steady-state driving voltage, meaningful improvements in operat ing voltage and luminance tuning from SL to DL. Luminance of about 10000 cd /m(2) was achieved for cells constructed in double-layer configuration, whe n one layer contains a mixture of polycarbonate and TPD, prepared by spinni ng technique.