Tandem White Organic Light-emitting Device Base On Novel Interconnecting Layer

With the rapid developing of science, the Organic Light-Emitting Device (OLED)has continued to progress to stable and mature especially in the areas of newgeneration of flat panel display technology. The Tandem White Tandem OrganicLight-Emitting Device (Tandem WOLED) is a device that installing two or moresingle organic electroluminescent units in series by the middle connection layeraccording to RGB three-color principle. The device has lots of advantage such asHigh brightness, low power consumption, long life; stable color coordinates and so on.So we have reasons to believe that it has a bright future.The intermediate connection layer (Charge Generated Layer， CGL) is essential forTandem WOLED. The operational mechanism of the CGL in the Tandem WOLED isthat the electrons and holes are first generated in CGL and then transported away fromCGL, and finally injected into the adjacent EL units. Therefore, design andoptimization of the intermediate connection layer of the stacked OLED play the mostimportant role in research work.This paper, based on all above research, study on tandem white organicelectroluminescent devices using a new intermediate connecting layer.We designed anew type of the intermediate connection layer, not only to ensure high performance oftandem device, but also to optimize the overall structure and the intermediate structureconnecting layer of tandem device.Specific carried out the following tasks：First of all, we use vacuum thermal evaporation method to fabricate monochromeOLEDs.We`ve three groups of devices：1、By comparing different electron transfer layer of yellow OLEDs, we find thedevice which has Bphen in its electron transfer layer has a higher ampere density andefficiency. So we draw the conclusion that when Ag deposit to three electron transferlayers (Bphen、TmPyPB and TpPyPB), it will diffuse into all three material, OnlyBphen could react to Ag and it promote electron’s injection from Ag to Bphen, reducethreshold voltage, improve the efficiency of the device. 2、 By comparing different thickness of Bphen of green OLEDs using Ag andBphen as cathode and electron transfer layer, we find the implanting of Bphen into Agand luminescent layer Alq3could promote cathode electron injection obviously, makethe electric current density magnified with voltage rising. Negative resistance effectwill disappear only when the thickness of Bphen rising to5nm. So we can draw theconclusion that the diffusion length of Ag deposition to Bphen is above5nm.3、 By comparing different yellow OLEDs using Ag and Mg-Ag alloy respectivelyas cathode, we find they have identical performances nearly. Using Ag as cathode notonly improve the electron injection, but also predigest any modified layer such asLiF、Alkali metals and their compounds、V2O5and so on. And the device using Aginstead of Mg-Ag alloy is easy to fabricate. So we can draw the conclusion that Ag isa good material in fabrication of OLED’s cathode.Second, we designed to use Ag as cathode and middle connection layer of TandemWOLED based on monochrome OLED which used Ag as cathode. We find that Agpromotes electron injection, rising electric current density obviously, and Ag is agood-performance material used in middle connection layer according to all above.Then we compare different electron transfer layer, Bphen show a better performancethan Ag. Considering the structure of Tandem WOLED, when the blue unit is closer toITO anode, the yellow unit is closer to cathode, the device show a more stableperformance. Even though electric current density and luminance are not influenced,efficiency will be rising obviously when ETL being thicker. It make Tandem OLEDhas a low turn-on voltage, low power efficiency, high power efficiency, stable colorcoordinate, and simplify structure. All above is owed to special relationship betweenBphen and Ag.Third, we designed the same material (Mg： Ag alloy) as a cathode applied to theTandem WOLED. Different concentration ratio of Mg： Ag and Ag are compared,because of the lower work function of Mg; even soaking Ag-a high work functionmaterial, an alloy is also suitable as the intermediate connection layer tandem device,and even better than Ag. Using Mg： Ag as the intermediate connection layer of the tandem WOLED，the efficiency can be improved.In summary, this paper design and optimize the intermediate connection layer ofTandem WOLED. Using Ag and Mg-Ag alloy as middle connection layer not onlysimplify device structure but also ensure a high performance. Tandem WOLED showslow driving voltage, high power efficiency and low efficiency rolloff.