Optimization of charge injection in the active emitting layer and balanced transport of carriers are important in realizing
high efficiency and good reliability in organic light emitting devices (OLEDs). Electrical doping of such molecular
materials with a view to enhancing their conductivity is an attractive route for enhancing the performance and versatility
of these optoelectronic devices, in particular by enhancing carrier injection and lowering operating voltages. In the
present study, we demonstrate efficient n-type doping of tris-(8-hydroxyquinoline) aluminum (Alq<sub>3</sub>) with the inorganic
insulator lithium fluoride (LiF) by co-evaporation. The effect of dopant concentration on charge injection and carrier
transport in this system is studied. We demonstrate that optimal doping not only leads to enhanced device currents and
lower operating voltages, but also changes the charge transport from trap-limited to space-charge-limited transport.
Using this scheme, we achieve efficient electron injection without using low work function cathodes. Finally, we employ
the optimally-doped electron transport layers in OLED architectures to demonstrate devices with enhanced efficiency
and lowered operating voltages.