| After more than 30 years of development in device engeneering and material design,the application potential of organic light-emitting diodes(OLEDs)has gradually been revealed.Among the OLEDs,the tandem OLED is a device with ultra-high efficiency and long operational lifetime.Tandem OLEDs electrically connect two or more light-emitting units(LEUs)through an intermediate connector,which have great advantages in the fields of display panels,solid state lighting and so on.However,tandem OLEDs still have many problems,such as device efficiency roll-off at high brightness,high driving voltage,and so on.As for the efficiency roll-off of a white organic light-emitting diode(WOLED),it is mainly due to the exciton quenching or carrier quenching effect within the light-emitting layer;as for the voltage loss,it is derived from the carrier injection barrier and the internal layer between the carrier-transporting layers or the malfunction of the intermediate connector.In this paper,we discuss the topic of hybrid WOLED efficiency roll-off,new"complementary intermediate connector" for the tandem WOLED,simplified tandem WOLED structure based on exciplex forming co-host.To response above questions,this thesis discusses the following aspects:In the first chapter,it summarizes the working principle of OLED and development of OLED structure,especially introducingesintroduces the advantages of tandem OLED and several major problems and feasible solutions of tandem WOLED at the present stage,as well as the main points of designing the connection layer,providing theoretical support and research basis for the thesis;In the second chapter,two kinds of blue thermally activated delayed fluorescence(TADF)materials have been synthesized.The materials not only behave great electroluminescent performance for blue OLEDs,but also have a balanced carrier transport ability as host materials for WOLEDs.It also serves as a blue luminescent material and a host material for a yellow dye for a WOLED light-emitting layer.A binary(B/Y)single-emitting layer(SEML)hybrid WOLED was fabricated to alleviate the triplet-triplet exciton quenching(TTA)effect in the luminescent layer,providing a basic method for designing a low efficiency roll-off SEML hybrid WOLED;In the third chapter,the hole transporting layer(HTL)material with a low ionization potential,m-MTDATA,is doped with HAT-CN,and applied to the intermediate connector of the tandem WOLED with white light emitting units.The structure of the intermediate connector is Bphen:LiH/HAT-CN/m-MTDATA:HAT-CN.The intermediate connector has a good charge generation effect,which is called a;'complementary charge generation layer'' When applied to a tandem WOLED,the driving voltage can be effectively reduced,the white light quality of the spectrum can be improved,and the device efficiency can be improved.In the fourth chapter,using the exciplex as the co-host for blue and yellow light-emitting units,the driving voltage of the device is further reduced,and the device structure is simplified.It turns out only 6 kinds of organic materials were used to prepare the tandem WOLED,which has a lower driving voltage of 5.9 V,and higher power efficiency of 79.7 lm/W.This simplified device structure has great application prospects in industrial production of solid-state lighting.In general,this thesis explores the high-efficiency and stable tandem WOLED,explains the main reasons and solutions for the WOLED efficiency roll-off.We also improved the intermediate connector structure of the tandem device,and uses the so-called "complementary charge generation layer" to enhance the charge generation capability.By using the exciplex as the co-host material in the LEUs,the hole injection barrier was reduced,resulting much lower driving voltage in the tandem WOLED and simplified device structure. |
PDF Full Text Request