Organic Light Emitting Diodes Using Doped Alq₃ as the Hole-transport Layer

Effects of 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4TCNQ)
doping on the hole conductivity of Alq₃ layer are measured. In the hole-only device of Alq₃, the current densities increase in 1--3 orders of magnitude upon doping with F4TCNQ, suggesting that the doping can effectively enhance the hole-injection and hole-transport ability of Alq₃. An organic
light-emitting device using an F4TCNQ doped Alq₃ layer as the hole-injection and hole-transport layer, and pristine Alq₃ as the electron-transport and emitting layer is fabricated and characterized. Bright emission is achieved in the simple OLED with p-doped Alq₃ as the hole-transport layer and the intrinsic Alq₃ as the electron-transport and emitting layer. The emitting efficiency and brightness of the device are further improved by inserting a thin electron block layer to confine the carrier recombination zone in the middle of the organic layers.