Highly Efficient Phosphorscent Organic Light-emitting Devices Based On Bipolar Host Materials

Organic light-emitting devices(OLEDs) is the third-generation optoelectronic display technology mainstream. Phosphorescent OLEDs have high efficiency, the emitting layer contains energy transfer from the host material to the dopant molecule, and then generate light-emitting. But bipolar host materials are very limited, the mixed-host(MH) structure constituting the bipolar charge transport properties, can significantly broaden the carrier recombination region, balance charge injection and transport, suppress crystallization and improve the performance of the devices. In this thesis, solution-processed phosphorescent OLEDs with bipolar host materials were fabricated and discussed.1. Highly efficient red phosphorescent OLEDs employing Ir(pq)2(acac) doped in small molecular CBP and TCTA were developed. Via solution-process, the devices with different mixing ratio of host materials with configuration of ITO/PEDOT:PSS/Ir(pq)2(acac): TCTA:CBP/TPBi/LiF/Al were fabricated. The performances, carrier injection/transport properties, film morphology and EL spectra of the fabricated devices were investigated.2. Soluble small molecular ternary-host system blue and deep blue phosphorescent OLEDs consisting of TAPC, mCP and OXD-7, green phosphorescent OLEDs consisting of CBP, TCTA and OXD-7 was investigated. By optimized the concentration of dyes, mixed ration and the thickness of functional layer, we obtained the efficient OLED devices. This topic provides broad prospects for low-cost devices, high efficiency, stable phosphorescent OLED applications.3. The group reported a bipolar host DNCzPO, following mixed-host idea, appropriate proportion of TAPC is used in the host materials. The excellent solution-processed PHOLEDs performance make those devices comparable with the best results from vacuum deposited devices with complicated structure. The solution-processed blue-emitting devices showed superior performance with high efficiencies(29.9 cd/A for current efficiency and 16.5% for external quantum efficiency), at 1000 cd/m2 the device showed low efficiency roll-offs.