Fabrication and characterization of electro-phosphorescent organic light-emitting devices with a ferromagnetic cathode for observation of spin injection effect

Organic light-emitting devices (OLEDs) with a phosphorescent molecule Ir(ppy)3 as the emitter and with an Fe cathode as the spin injector were fabricated for the observation of the large degree of circular polarization. The OLED structure was a glass-substrate/ITO/α-NPD/CBP doped with Ir(ppy)3/BCP/Al-oxide/Fe/Al. The mixing ratio of CBP and Ir(ppy)3 in the emissive layer was optimized for high luminescence efficiency. The OLEDs showed circular polarization, and the maximum degree of circular polarization of the OLEDs was 0.4% at the applied magnetic field of 1.6 T at room temperature. On the other hand, no circular polarization was observed from the OLEDs with an Al cathode.