HIGH-EXTERNAL-QUANTUM-EFFICIENCY ORGANIC LIGHT-EMITTING DEVICES

We study the internal and external quantum efficiencies of vacuum-depo sited organic light-emitting devices (OLED's). The internal quantum ef ficiency of OLED's based on tris-(8-hydroxyquinoline) aluminum is calc ulated to be 5.7 times the observed external quantum efficiency eta(e) , consistent with measurements. We demonstrate a shaped substrate that increases eta(e) by a factor of 1.9 +/- 0.2 over similar OLED's fabri cated upon flat glass substrates and leads to a 100%-emissive aperture , i.e., the emitting area completely occupies the display area even in the presence of metal interconnects. We also discuss a substrate stru cture that increases eta(e) by an additional factor of 2. The high dev ice efficiencies are promising for developing OLED-based displays with extremely low power consumption and increased operational lifetime. ( C) 1997 Optical Society of America.