Device Engineering Of High-Efficiency Organic Light-Emitting Diodes Based On Novel Exciplex Host

OLEDs have many attractive characteristics for next-generation display and solid-state lighting applications,such as light weight,thin,flexibility,low power consumption and wide color gamut.Although small-sized and TV-sized OLED displays as well as a small number of OLED lighting panels are commercially available,it is still very challenging for us to pursue higher efficiency,longer lifetime and lower cost of OLED panels.By using exciplex as the host of emitting layer,the intermal quantum efficiency(IQE)can reach nearly 100%because of the Thermally Activated Delayed Fluorescence(TADF)process.In my thesis,I have adopted several approaches based on exciplex to acquire high-efficiency OLEDs.First,an ultra-efficient white OLED was fabricated based on a newly designed bulk-exciplex host.The bulk-excplex not only has the effect of thermally activated delayed fluorescence(TADF),but also possesses an internal quantum efficiency of 100%.The exciplex host and emitters Flrpic and PO-01 were characterized by photoluminescence spectroscopy,electroluminescence spectroscopy,transient fluorescence,and ultraviolet visible spectroscopy.The resulting white OLED delivered an unusually high forward?viewing luminous efficiency of 105.0 lm W'1 and extermal quantum effmciency(EQE)of 30%(without using any optical out-coupling techniques).Such high efficiencies and excellent device performance should benefit from the advantages of exciplex material solely used as the host.Furthermore,multi-quantum-well structure based on an interface-exciplex host was applied to green OLEDs.Because of the use of an ultra-thin emitting layer,the complex doping process can be avoided.The structure not only significantly improves device power efficiency,but also simplifies the fabrication process,thus it has a great potential in lowering the cost of OLED panels.By using this structure for green-emitting OLED,the device has a high luminous efficiency about 94 lm W-1.More impressively,the efficiency roll-off of EQE(at 10000 cd m-2)was greatly improved from 89.8%to 30.1%by using the multi-quantum-well structure.Therefore,we believe that OLEDs based on the exciplex host will show great potential in the future.