We show that doping of the transport layers can strikingly improve the properties of organic light emitting diodes (OLEDs). The electroluminescence onset voltage of diodes containing an vanadyl–phthalocyanine (VOPc) hole transport layer intentionally doped with tetrafluorotetracyano-quinodimethan(F4-TCNQ)is reduced by up to an order of magnitude compared to OLED with undoped VOPc. The improved properties of our devices can be explained by the improved conductivity and better injection for a doped transport layer. ©1998 American Institute of Physics.