Optical Radiation Performance Of Multi-component Single-emission Layer And Application In OLED

Organic light-emitting device(OLED),as the core of the third-generation display technology,has entered the commercialization stage from the technology researth stage.At present,most industrialized OLEDs are prepared by vacuum deposition mainly,and the harsh conditions of high vacuum and high temperature increases the complexity of preparation and reduces the utilization rate of materials.What's more,its large-area is problematic because of the difficulty of depositing several components simultaneously in the same layer precisely.Solution-processed OLED has the advantages of high material utilization rate,high processing efficiency,good compatibility with flexible substrates,and easy to control the proportion of components,etc.But the device has poor stability and serious efficiency roll-off.In this thesis,some"star molecules"in the field of organic light emission were studied in depth,including thermally activated delayed fluorescent materials,polymer host materials,organic photosensitizing materials,and the co-emission characteristics of these materials.A series of OLEDs based on a single-emission layer were designed,and the working mechanism of the devices was studied.We obtained many adjustable optical properties and high efficiency devices,and provided a reference for high efficient OLEDs with tunable colors and large-area white light by solution-processed.The dissertation is comprised of the following three parts:(1)Solution-processed TADF-OLEDs based on tunable colors:We used four kinds of TADF materials,named 4Cz IPN,DMAC-DPS,DDCz TRz,2Cz DPS,and the exciplex was formed when doped them in pairs to prepare optical films.On this basis,we prepared six different systems devices through solution-processed method,and then found that all systems achieved color tuning.4Cz IPN:DMAC-DPS system obtained the best regularity of the toning range,the EL peak wavelength range was from 484 nm to 556 nm,the FWHM was from 86 nm to 130 nm,and the spectrum-covering region range from sky-blue to yellow-green,achieved a wide toning range of emission colors.The maximum current efficiency and maximum external quantum efficiency of4Cz IPN:DDCz TRz system achieved 28.0 cd/A and 9.6%,and the device still maintained a high current efficiency of 20.0 cd/A at 10 000 cd/m~2.Thin-film morphology was also addressed and found the film was uniform and dense.Additonally,the light-emitting mechanism of the device was studied throght comparing the PL process with EL process.The results showed that under the excitation of the electric field,TADF materials realized two RISCs between intermolecular and intramolecular,which increased the exciton utilizationrate.(2)Solution-processed TADF sensitized devices based on different host:We used two different hosts materials named PVK and 26DCz PPy.The possibility of F?rster energy transfer from host to guest was found throught exploring their UV and PL characteristics.In additon,two systems devices with different hosts were prepared.Compared with device based on PVK host,device based on 26DCz PPy host achieved higher brightness and higher efficiency.After optimization,when4Cz IPN:DMAC-DPS=1:1 and the total doping is 20%,the maximum current efficiency and maximum external quantum efficiency achieved 35.7 cd/A and 11.8%,respectively.What's more,the device still maintained a high external quantum efficiency of 10.0%at 5000 cd/m~2,achieved a low efficiency roll-off.Then we designed experiments to analyze the reasons for its high performance.DMAC-DPS as a assistant promoted the effective upconversion of triplet excitons,and increased the effective F?rster energy transfer channel from DMAC-DPS to 4Cz IPN,so greatly improved exciton utilization.At the same time,it was found that the distribution of DMAC-DPS sensitizer and 4Cz IPN guest in the 26DCz PPy host was uniform,the good thin-film was beneficial to the stability of the device.(3)Solution-Processed WOLEDs based on mixed host:Three types single-emission layer WOLEDs with mixed host of TAPC:TCTA:PVK:OXD-7 were prepared by solution-processed method,achieved high color quality and efficiency.The binary blue/orange WOLEDs exhibted a turn-on voltage of 3.4 V,a maximum current efficiency of 25.9 cd/A,an EQE of 11.0%,a device maximum brightness of 34 916 cd/m~2,a CIE of(0.375,398),a CRI of 67,and a CCT of about 4000K.The optimized blue-green-orange three component WOLEDs showed a warm-white emission with a CCT of 3730 K,CRI of 71,CIE of(0.423,0.403),a low turn-on voltage of 2.8 V,and maximum current efficiency reached 30.9 cd/A,EQE of 11.9%.In order to get a higher quality lighting source,blue-green-orange-red four component WOLEDs were fabricated by introducing a red compontent,with a wider spectral region,a CRI of 77,a CIE of(0.411,0.432),a turn-on voltage of 3.5 V,a high current efficiency of 23.4 cd/A,and an EQE of 9.8%were obtained.