Structure Design And Performance Study Of White Organic Light-emitting Diodes From All-exciplex Emissions

White organic light-emitting diodes(WOLEDs)have the advantages of surface light sources,as sunlight,low power consumption,and flexible preparation.And WOLEDs have great potential in the field of solid-state lighting and full color panel display,becoming a major research hotspot in recent years.The discovery of thermally activated delayed fluorescence materials has greatly improved the efficiency of all-fluorescent-based WOLEDs,but there are still the problem of low color rendering index and so on.Exciplexes have broad spectral emission characteristic,which makes they have natural advantage in developing high-color quality WOLEDs.Especially,exciplexes with thermally activated delayed fluorescence effect have discovered in recent years,which has also shown great potential in improving the efficiency of WOLEDs.However,the reports about all-exciplex-based WOLEDs are still few.And there are problems such as complex structure,complicated preparation process and low device efficiency.Based on this,this paper combines the inherent characteristics of the exciplexes,and designs simple and novel device structure to achieve the improvement of device performance and spectra,successfully developing a series of highefficiency and high color rendering index of all-exciplex-based WOLEDs.The specific research contents are as follows:1.All-fluorescent-based WOLEDs combining blue exciplex emission and yellow fluorescence emission.Blue-yellow complementary white emission is achieved by doping the novel yellow fluorescent material into the blue exciplex m CP:PO-T2 T.Incomplete energy transfer from blue exciplex to the yellow fluorescent material Y is realized by adjusting the doping ratio of the yellow material Y in the blue exciplex.The external quantum efficiency of the optimal WOLED reached 8.22%,far exceeding the theoretical limit of the fluorescent device.2.Developing sandwiched light-emitting structure all-exciplex-based WOLEDs with high color rendering index.In order to solve the problem of low color rendering index,we proposed a sandwiched device structure,which is that two blue exciplex sandwiched a yellow exciplex in the middle.WOLEDs with all-exciplex emission are constructed.By adjusting the thickness of the blue exciplex on both sides and the doping ratio of donor and acceptor that forming the middle yellow exciplex,the carrier recombination region and exciton distribution of the device were successfully controlled.A series of high-efficiency and high color rendering index of WOLEDs are developed.The optimal WOLED achieves a high color rendering index reaching 86 and current efficiency reaching 7.89 cd/A.3.Proposing all-exciplex-based WOLEDs with complementary emission at the interface.We alternately deposited exciplex acceptor TPBi which can form blue exciplex with TAPC and exciplex acceptor PO-T2 T which can form yellow exciplex on the same exciplex donor layer TAPC in vertical direction.And accurately controlling the distribution of different exciplex acceptor materials on the exciplex donor layer,white emission can be realized by combining blueyellow complementary exciplex emission formed in the same exciplex donor layer interface.A series of WOLEDs were successfully prepared using this novel and simple structure.Among them,the color rendering index of WOLED with bisected blue-yellow regions achieved 71 and the maximum current efficiency is 3.17 cd/A.The device performance and spectra can be adjusted and improved by simply changing the arrangement of different acceptor layers on the same exciplex donor layer,which provides a new idea for designing the WOLEDs device structure.