The Investigation Of New-style Hosts And Their Applications In Solution-processed Organic Light-emitting Diodes

Organic light emitting diodes(OLEDs)have been extensively developed from fundamental research to commercial products.Gradually,they replaced conventional displays and have been one of the most concerned research topics.Although,organic materials for OLEDs are abundant,there are still many new problems and mechanisms to be solved.For a long time,the researches on the hosts are very remarkable,because the appropriate hosts not only can improve the excitons utilization of the devices,but also play a significant role in inhibiting the aggregation-caused quenching(ACQ)of guest molecules and reducing the non-radiative transition.In this thesis,the hosts with different characteristics are studied to obtain highly efficient solution-processed OLEDs and promote the development of large-size and low-cost OLEDs.Chapter 1 is a literature review,which introduces the developments of OLED and related background knowledge.Then,the relevant literatures about the hosts and the guests are discussed,respectively.Finally,the idea and main contents of this thesis are briefly described.Chapter 2 confirmed the formation of exciplex between the hole-transporting materials m-MTDATA and the bipolar host o-CzOXD.What is more,the exciplex can be an excellent host for deep red OLEDs.With the host,the approximately saturated red emission and a maximum external quantum efficiency of 11.9% were achieved,which was 6.6 times higher than the previously reported efficiency based on the guest emitter doped in the polymer-based co-host.An efficient way was provided to improve the utilization of excitons of the devices.In Chapter 3,a more convenient and effective method was proposed to inhibit the aggregation-caused quenching of conventional fluorescent materials and expand the application of such molecules in the field of organic solids.We chose benchmarking materials TPE with aggregation induced emitting(AIE)property and m-ACSO2 with aggregation enhanced emitting(AEE)property respectively to be the hosts for the conventional fluorescent materials which are very prone to aggregation quenching.The AIE and AEE properties of the hosts were transferred to the guests through F?rster energy transfer process.The method can be widely applied to many cases in which the fluorescence emitters with concentration quenching effect have to be employed.Based on the first two chapters,Chapter 4 employed the thermally activated delayed fluorescent molecule m-ACSO2 with the AEE property as the host and three traditional fluorescent polymers with ACQ property as the guests to prepare solution-processed devices.The utilizations of the excitons in the devices were improved and the ACQ phenomena of three guests were alleviated.The device based on the polymer F8 BT realized the maximum current efficiency of 11.0 cd/A,which was 13.8 times and 2.6 times higher than that of the non-doped device and the reference one based on the mCP host,respectively.The devices based on the other two analogue polymers have also been improved with the same strategy.This strategy could be a universal one to promote the performances of solution-processed OLEDs.Chapter 5 summarized the main contents of this thesis.And we believe that developing excellent host is an important propellant for reducing the cost of organic optoelectronic devices.