| Organic light emitting diodes(OLEDs)have attracted widespread attention due to their advantages such as high brightness and low driving voltage.Solution processed technology was regarded as the key to the preparation of large-size and flexible devices,which conforms to the development direction of OLED.The dissolution of organic small molecule functional materials of OLEDs in solvents is critical for the preparation of inks toward solution processed devices.For some kinds of currently used materials which are not highly soluble in common solvents that suitable for printing processing,the applications in solution processed OLED devices would be limited.And the dissolution between the interfaces of the organic layers during multi-layer printing also restricts the development of solution-processed technology.The nanonization of organic small molecule materials offers a feasible method to prepare the solution of organic functional materials in the poor solvents.In this paper,the OLED small molecule material nanoparticles were prepared by solvent anti-solvent precipitation method,and the ink prepared from the nanoparticles was spin-coated into a film.The main contents are as follows:(1)The solubility of 1,3,5-tris(1-phenyl-lH-benzimidazol-2-yl)benzene(TPBi),a small molecule electron transport material,in 12 kinds of organic solvents was determined by the isothermal saturation method.In all the solvents measured,the solubility of TPBi gradually increased as the temperature increasing.A solubility model had been established,and the experimental results were basically in agreement with the calculated results.(2)The TPBi nanoparticles were prepared by the solvent anti-solvent precipitation method,and the optimal experimental conditions were explored.When the solvent was THF,the anti-solvent was water,the ratio was 1:10,the stirring rate was 800 rpm,the stirring time was 0.5 min,and the concentration was 0.5 mg/mL,the size of TPBi nanoparticle was 119 nm.The anti-solvent precipitation process was strengthened by high gravity technology,and the particle size was further reduced to 40 nm.The solubility of nanoparticles has been improved,which was 1.25 times than that of raw materials in ethanol.The prepared ink was spin-coated into a film,and the optimal film-forming conditions were explored.Compared with the film prepared with raw materials,the roughness of the film prepared with nanoparticles was greatly reduced,which was only 0.325 nm,and the transmittance of visible light was also improved.(3)The OLED host material 4,4'-bis(9-carbazole)biphenyl(CBP)nanoparticles were prepared by the solvent anti-solvent precipitation method,and the influence of different experimental conditions on the morphology of the nanoparticles was explored,under which the particle size was 220 nm.The high-gravity anti-solvent precipitation method was used to further reduce the particle size to 170 nm.The saturation concentration of the ink prepared with nanoparticles significantly increased by 20%when ethyl acetate was used as the solvent.The dissolution rate was also increased,the nanoparticle solution was saturated in 20 minutes,while the concentration of the raw material was only 56%of the saturated concentration at this time.The phosphorescent material Ir(mppy)3 was doped with CBP to prepare the light-emitting layer.Compared with the raw material,the roughness of the doped film of CBP nanoparticles was greatly reduced,only 0.910 nm.In order to prevent mutual dissolution at the interface,the orthogonal solvents(ethyl acetate and ethanol)were used to dissolve the light-emitting material and the electron transport material to prepare a double-layer film.Compared with the single light-emitting layer,the fluorescence intensity did not decrease significantly,indicating that the interfacial dissolution was inhibited. |
PDF Full Text Request