Fabrication And Performance Of The Single Emissive Layer White Organic Light-Emitting Diodes With Iridium Complex Dopants

White organic light-emitting diodes have the merits,such as high efficiency,low power consumption,self-illumination,ultra-thin and ultra-light,environmental-friendly,soft light,no dazzle,flexible panel display and so on.There is a broad application prospect in the field of color display and solid state lighting,which is favored by researchers.With the development of technology,we have realized commercial applications from laboratory to market.However,at present,the efficient white organic light emitting diodes are mainly prepared by vacuum evaporation,which is faced with the disadvantages of low material utilization rate,complex preparation process,high device preparation cost and so on,which constrains its commercial application.Solution-processing technology has the advantages of low cost,high material utilization,simple fabrication,low energy consumption,which is an important development direction of commercial application,whereas solution-processed white organic light emitting devices are faced with low device efficiency,serious efficiency roll off,poor color coordinate stability,low color rendering index.Basing on the above issues,we prepared solution processing white organic light emitting devices and systematically studied the influence of different guest,different host,different device structure on device performance.The main research content and research results are as follows:1 We fabricated ternary single emissive layer solution processed white organic light emitting diodes by using the nitrogen-carbonyl fluorescent material QPXO,cyclometalated iridium complex phosphorescent material（2Fppy）₂Ir（3-OMepzic）as blue dopant,the traditional phenylisoquinoline cyclometalated iridium complex Ir（piq）₂（acac）as red dopant,using polyvinylcarbazole（PVK）and 1,3-bis（9-carbazolyl）benzene（m CP）as host.The QPXO and（2Fppy）₂Ir（3-OMepzic）were synthesized in our laboratory and the Ir（piq）₂（acac）was purchased by commercial way.The experiment result shows that,1)when the doping ratio of QPXO:Ir（piq）₂（acac）is 10:0.6,the maximum external quantum efficiency(EQE_max)presented by the device is 1.54%,,while the CIE and CCT are（0.308,0.381）and 6373 K with QPXO as blue dopant and PVK as host;2)When the doping ratio of QPXO:Ir（piq）₂（acac）is 10:0.4,the EQE_max of the device is increased to 2.08%,the CIE is（0.324,0.391）and and the color temperature is reduced to 5760 K;3)When we changed phosphor（2Fppy）₂Ir（3-OMepzic）as blue dopant,the doping ratio is 10:1.0,the EQE_max is further increased to 7.73%,the maximum luminance is high up to 13290 cd/m²,the CIE is（0.415,0.359）and CCT is 2992 K.By changing the electron injection layer to Li F,the EQE_max of the device is further optimized to 8.94%,and CIE is（0.390,0.350）.The performance of ternary single emissive layer WOLEDs was improved effectively by the optimization of host material,guest material and device structure.2 Binary and ternary single emissive layer solution processed white organic light emitting diodes were fabricated by using 2,3-diphenylpyrazine cyclometalated iridium complex（DP）₂Ir（dpm）as orange dopant and the blue dopant are traditional thermal activated delayed fluorescence（TADF）materials Cz Ac SF,DMAc-TRZ and phosphor material FIrpic,respectively,and small molecule m CP was applied as the host material.The effects of orange/blue guest material composition,proportion and molecular structure of the host material on the performance of WOLEDs were studied.The results show that,1)when the doping ratio of（DP）₂Ir（dpm）is 1.75 wt%,with the turn-on voltage is only 3.6 V in binary WOLEDs based on Cz Ac SF and（DP）₂Ir（dpm）,the device shows the optimal electroluminescence performance demonstrate the EQE_max of 7.89%and the CIE of（0.380,0.383）and the CRI of 71;2)When the doping ratio of Cz Ac SF:（DP）₂Ir（dpm）is 10:0.6,the maximum EQE of the device is 10.50%,the CIE is（0.454,0.395）and the CRI is only 66 in ternary WOLEDs based on Cz Ac SF and（DP）₂Ir（dpm）doped with m CP;3)We prepared ternary WOLEDs using TADF material DMAc-TRZ with higher photoluminescence quantum yield as blue component.When the doping ratio of DMAc-TRZ:（DP）₂Ir（dpm）is 10:1.0,the EQE_max of the device is increased to 10.94%,the CIE is（0.356,0.438）and the CRI is increased to 73,the maximum brightness is 17850 cd/m²,and a moderate CCT of 4918 K;4)We fabricated ternary WOLEDs using blue phosphor FIrpic instead of TADF material as blue guest material.When the doping ratio of Flrpic:（DP）₂Ir（dpm）is 10:0.6,the device shows the best electroluminescence performance and the maximum EQE reached 17.19%,the maximum brightness and CRI can still reach 18230 cd/m² and 75,and the CIE is（0.344,0.399）.We realized efficient ternary single emissive layer WOLEDs based on cyclometalated iridium complex（DP）₂Ir（dpm）by using Flrpic:（DP）₂Ir（dpm）double phosphorescent guest material strategy instead of DMAc-TRZ:（DP）₂Ir（dpm）phosphorescent-TADF guest material strategy and optimizing the ratio of guest material.3 We prepared ternary single emissive layer solution processed WOLEDs using the cyclometalated iridium complex（2Fppy）₂Ir（piq）with binary C^N ligand as orange dopant,combining blue TADF material Cz Ac SF and phosphor FIrpic.The effects of different guest materials,hole transport layer PVK,exciton block layer DPEPO to the performance of WOLEDs were systemic studied.The research results show that,1)In ternary WOLEDs based on Cz Ac SF and（2Fppy）₂Ir（piq）,when the doping ratio of Cz Ac SF:（2Fppy）₂Ir（piq）was 10:0.6,the device realizes the EQE_max of 9.10%,and the CIE,CCT and CRI are（0.433,0.322）,2407 K and 65,respectively.It is warm white emission and the turn-on voltage is only 4.4 V;2)In ternary WOLEDs based on FIrpic and（2Fppy）₂Ir（piq）,when the doping ratio of FIrpic:（2Fppy）₂Ir（piq）is 10:1.8,the device shows great performance,the maximum EQE of the device is 11.18%,the CIE,CCT,CRI are（0.445,0.385）,2705 K and 67,respectively.The maximum brightness can still reach 13090 cd/m²;3)The introductionof hole transport layer of PVK and exciton block layer of DPEPO can improve the performance of the device.When we introduced the hole transport layer of PVK,the maximum EQE of the device was raised to15.00%.While the maximum brightness was still up to 11260 cd/m².Further inserting the DPEPO layer,the maximum EQE was further improved to16.36%,with the increase of CIE（0.359,0.373）and CCT 4607 K,respectively,while the CRI was still high up to 71 which is close to standard white light.By optimizing the guest material,the hole transport layer and the exciton block layer are introduced,and the（2FPPy）₂Ir（piq）cyclometalated iridium complex doped with high-efficiency electroluminescence of the ternary single light layer WOLEDs is achieved.