| The solution-processed high efficient blue organic light-emitting device(OLED)is the hot spot of research in recent years,in which the thermally activated delayed fluorescent luminescence(TADF)materials are often used as the luminescent materials due to their high internal quantum efficiency of theoretically up to 100%.However,due to the low solubility of small molecule blue TADF materials in organic solvents,the morphology of the films prepared by solution method is very poor,and the mismatch of energy levels between functional layers makes carrier transmission difficult.Those factors make the device performance of solution-processed TADF OLEDs suffers a lot compared with the one fabricated by vacuum evaporated.In this paper,solution-processed blue TADF OLEDs were fabricated based on the high efficient blue TADF mall molecule material DMAC-DPS.On the basis of the optimization of the basic preparation parameters,the film morphology of the emission layer(EML)prepared by mixed solvents was optimized,and the PEDOT:PSS was doped with PSS-Na to adjust the hole injection and transmission characteristics.Their effect on device performance and mechanism contains has been studied,and main work was listed as shown below:First of all,the experimental conditions were optimized for the solution-processed OLEDs with DMAC-DPS.The photoluminescence of the film prepared by the solution method showed a sky blue color with a peak of 480 nm.The effects of spin coating process on device performance were studied,and the corresponding optimal preparation parameters were obtained.The differences between the morphology of the films prepared by vapor deposition and solution method were compared and analyzed,and it is speculated that the interface problem is the key factor affecting the device performance of the solution processed OLEDs.Secondly,considering the low solubility of organic small molecular materials in organic solvents,mixed synergistic solvents(chloroform/chlorobenzene)were used in blue TADF OLEDs to prepare the EML to combine high solubility and film quality.Firstly,the changes of the morphology of the films prepared with different mixed ratios were analyzed.The morphology of the films was improved with the addition of chlorobenzene and the film morphology showed a large tolerance to the CB concentration.Carrier transport benefited from the improved film morphology.By comparing the current density of the single carrier device,the carrier transport of the film prepared by the mixed solvent is obviously improved.The carrier activity inside the device was studied,and the carrier accumulation at the interface of the device was reduced.At the same time,it was verified that the mixed solvents had little effect on the internal defects of EML.Finally,As expected,the blue OLEDs employing synergetic solvent strategy presents an increment of 22.8%in device efficiency and 19.4%in luminescence,which reaches the highest efficiency of 15.76 cd/A and an efficiency of 9.63 cd/A at a luminance of 1000 cd/m2.Finally,when PEDOT:PSS is used as the hole injection layer(HIL),considering the serious carrier accumulation at the interface between HIL and EML,the mixed HIL was prepared with doping PSS-Na into PEDOT:PSS to enhance the work function.Different doping ratios are set to observe the improvement of the electrical performance of the device.When the doping ratio is 0.7:0.3,the device efficiency presents an optimally increment of 42.6%,which reaches the highest efficiency of 20.14 cd/A.The photoelectric properties of the hole injection layer after doping PSS-Na were observed,and the film conductivity decreased,but the corresponding work function was improved.By observing the carrier activity inside the device,it is found that the carrier accumulation at the interface between HIL/EML was reduced with the incorporation of PSS-Na,and got more obvious as the ratio of incorporation increases. |
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