Efficient and saturated blue organic polymer light emitting devices with an oxadiazole containing poly(fluorene) polymer emissive layer

A new series of organic light emitting copolymers, poly(dioctyl fluorene -co diphenyl oxadiazole)s P(DOFDPO), are reported in this paper. We found organic polymer light emitting devices with comparable device efficiency and more saturated blue color based on this new series of copolymers with less than 10% DPO moiety when compared with poly(dioctyl fluorene) P(DOF) devices. The device structures used in this study were indium tin oxide (ITO) anode / PEDOT-PSS layer / emissive layer / calcium (Ca) / aluminum (Al) cathode, while the emissive layer was P(DOF) or P(DOF-DPO) copolymer with different DOF and DPO ratio. The AFM data shows that the emissive layer has a smooth surface with RMS roughness of about 0.5 ± 0.2 nm over a 2 μm by 2 μm area. The photo-luminescence quantum efficiency of the P(DOF-DPO) copolymer decreases with increasing DPO moiety. Both the photo-luminescence spectra and electro-luminescence spectra are slightly blue shifted when adding less than 10% DPO moiety into P(DOF). Both the emission efficiency (~0.3-0.6 cd/A at 100 cd/m) and power efficiency (~0.1-0.2 lm/W at 100 cd/m) of the P(DOFDPO) based PLEDs with less than 10% DPO moiety are comparable to the P(DOF) based PLEDs.