Doped organic light emitting diodes having a 650-nm-thick hole transport layer

We have succeeded in fabricating a thick-film organic light emitting diode having a doped hole transport layer (DHTL). The basic cell structure is anode DHTL/emitter layer/cathode. The DHTL is composed of a hole transporting polycarbonate polymer (PC-TPB-DEG) and tris(4-bromophenyl)aminium hexachloroantimonate (TBAHA) as a dopant. As an emitter, we used tris(8-hydroxyquinoline) aluminum (Alq). With a 650-nm-thick DHTL, the device showed considerable reduction in cell resistance compared with an anode/nondoped HTL/Alq/cathode device with the same HTL thickness. Although the electroluminescent quantum efficiency ΦL was rather low in the doped device, we should be able to increase it by interposing a thin tetraphenylbendidine (TPB) layer between the DHTL and the emitter layer while keeping the driving voltage low. The anode/DHTL (650 nm)/TPB(50 nm)/Alq(50 nm)/cathode showed luminance of more than 4004 cd/m2 at 10.0 V and 220 mA/cm2.