Highly Efficient And Roll-off Of Solution-Processable Organic Light-Emitting Diodes

Organic light-emitting devices(OLEDs) have well-recognized advantages in simple structures, low driving voltage, flexibility and large areas. In particular, phosphorescent OLEDs(PhOLEDs) are highly attractive due to their potential for achieving unity internal quantum efficiency through harvesting both singlet and triplet excitons. At present, it is also difficult to achieve phosphorescent OLEDs of high efficiency, high stability and low current efficiency roll-off. However, research on device, it is very meaningful to do research on broaden the carrier recombination region, balance charge injection and transport, suppress crystallization. The emission mechanism of TADF for OLEDs was first and influentially presented by Adachi group of the Japanese scientists in the Nature journal, reported that the external quantum efficiency of the device exceeds that of the traditional fluorescent device. And intensive interests have been drawn to the report. Recently, TADF based OLEDs have get fast development, and monochrome device efficiency has reached the efficiency of phosphorescent OLEDs. This has an important practical significance to reduce the cost of the device and accelerate industrialization. In this thesis, solution-processed phosphorescent OLEDs with high efficiency and low roll-off were fabricated and discussed, TADF based OLEDs were also fabricated and discussed.1. The group reported a series of solution-processible arylfluorenes(AFs)/cabazole hybrid compounds(SmeFCz, DMeFCz, SMeOFCz, DMeOFCz, SFFCz and DFFCz). These compounds exhibit good thermal stability, excellent solubility and high triplet energy levels, which can be used as universal hosts for solution-processed phosphorescent organic light-emitting devices(PhOLEDs). Employing the developed materials, highly efficient blue(DMeFCz: CEmax: 20.0 cd/A, EQEmax: 10.0 %), green(DMe FCz: CEmax: 26.0 cd/A, EQEmax: 7.8 %) and red(SMeFCz: CEmax: 13.7 cd/A, EQEmax: 8.2 %) PhOLEDs fabricated by spin-coating in different device configurations have been demonstrated. Furthermore, complementary-color, single layer white phosphorescent device were also obtained. The SMeOFCz-based white device exhibited highly efficient white-light emission with a maximum efficiency of 27.1cd/A(EQE of 12.0 %). The state-of-art performance indicates that AFs/cabazole hybrid hosts have a favorable prospect of applications in solution-processed full-color displays and white PhOLEDs2. High efficiency hybrid type white OLEDs and sensitized red fluorescent OLEDs based on TADF materials. The high efficiency white OLEDs combining a green thermally activated delayed fluorescent(TADF) emitting materials with red/blue phosphorescent emitting materials. Then according to the broad emission spectra and a small singlet-triplet energy gap of TADF materials. Here, we use 4CzCNPy as sensitizing hosts for conventional fluorescent dopants.By optimizing the doping concentration of the dye, and the mixing ratio of the hostmaterials and the functional layer thickness to obtain high efficiency red OLEDs. This part of work provide a bright future for low-cost, high efficiency and stable OLEDs devices.3. Highly efficient red and blue phosphorescent OLEDs based on small host molecule mCP with electron or hole materials. Via solution-process, the device with different mixing ratio of host materials with the configuration of ITO/ PEDOT:PSS/ Ir(pq)2(acac) or FIrpic: mCP:co-host/ TmPyPb/ Li F/ Al were fabricated. The performances, carrier injection/transport properties, film morphology and EL spectra of the fabricated device were investigated. This part of work provides a reliable way of thinking for the study of the solution-processed devices which have high efficiency, high stability, low roll-off, and provides an important basis for further study of other color phosphorescent OLEDs devices.