Design,Synthesis And Device Engineering Of Phosphorescent Host Materials For Organic Light Emitting Diode

Organic light emitting diode(OLED)has aroused much more attention during the past decade and been applied in many flat panel displays and solid state light sources because of its superior performance such as light and thin,high efficiency,low power consumption and vivid color.The efficiency of OLED has been greatly improved in recent years owing to the advancement of phosphorescent materials which have an internal quantum efficiency of 100%.Much attention has been paid to host materials with the development of phosphor materials.Phosphor materials are usually doped into the host materials for better energy transfer from the hosts into the emitters such that the OLEDs can have a higher luminous efficiency.In my thesis,I mainly focus on the design of host materials for highly efficient phosphorescent OLEDs.Firstly,it is commonly believed that introducing sp2 nitrogen into the backbone of the conjugate structure can improve the electron transporting property,so we introduce sp2 nitrogen into azafluorenone to obtain 1,4 diazafluorenone.We eventually design and synthesize 3 phosphorescent host materials,namely 10-phenyl-10H-spiro[acridine-9,9'-indeno[1,2-b]pyrazine](SAIP),10-phenyl-10H-spiro[acridine-9,11'-indeno[1,2-b]quinoxaline](S AIQ)and 10-phenyl-10H-spiro[acridine-9,13'-benzo[g]indeno[1,2-b]-quinoxaline](SABIQ).Red OLED based on SAIQ as the host shows a maximum external quantum efficiency of 21.1%,compared to 16.6%if a conventional host,9,9'-(1,3-Phenylene)bis-9H-carbazole(mCP)is used for the device fabrication.Secondly,we introduce an electron-donating triphenylamino group and a tertiary butyl group into the dispiro[fluorene-9,9'-anthracene-10',9"-fluorene](DSFA)and dispiro[acridine-9,9'-anthracene-10',9"-acridine](DSAA),respectively and obtain 4 new phosphorescent host materials.By optimizing their physical and chemical properties,green OLED using 4-(dispiro[fluorene-9,9'-anthracene-10',9"-fluoren]-2'-yl)-N,N-diphenylaniline as the host exhibits a maximum power efficiency of over 100 lm/W.Finally,different from traditional OLEDs using only single hosts,we use 4,4'-bis(9-carbazolyl)-2,2-dimethylbiphenyl(CDBP)and 4,6-bis[3,5-(dipyrid-4-yl)phenyl]-2-methylpyrimidine(B4PyMPM)to form an exciplex co-host.Benefit from the up-conversion properties of exciplex which can then fully utilize the singlet and triplet excitons,we have demonstrated highly efficiency green,orange and red OLEDs.Then we use the aforementioned exciplex as the orange host together with another group of exciplex,2,6-bis(3-(carbazol-9-yl)phenyl)pyridine(26DCzPPy)and B4PyMPM,as the blue host to construct warm white OLEDs.For this two-color white OLED,we achieve a maximum power efficiency of 104.6 lm/W and an external quantum efficiency of 30.9%.