Study On The Preparation Of Printing OLED Nanomaterials By High-gravity Technology

Organic light emitting diode(OLED)is a new generation of lighting and display technology.It is considered to be one of the most promising new flat panel display technologies due to its outstanding advantages such as self-luminescence,wide color gamut,wide viewing angle,high contrast,and fast response.Printing OLED technology is one of the effective ways to solve high cost,improve material utilization and realize flexible large-area display panel fabrication.However,as an emerging technology,there is poor compatibility and low maturity between the teniques and materials of printing OLED.General research tends to focus on the pursuit of high performance brought about by molecular design and ingredient formulation,while ignoring the constraints of subsequent engineering production and practical process applications.In turn,it is difficult to coordinate the material properties and process requirements to maximize the efficiency.One of the derived common problems is the limited choice of materials for printing OLED inks due to solubility limitations.In this thesis,starting from the dissolution and dispersion mechanism of nano-and micro-scale materials,a new idea of using printing OLED nano-ink to broaden the choice of substrates is proposed.Guided by this,high-performance OLED organic small molecule interface materials and conjugated polymers were selected as research objects.The advantages of high-gravity enhanced molecular mixing and mass transfer were used to develop a simple and efficient preparation process and technology for OLED nano-and micro-scale materials,and a variety of nanomaterials and their hydroalcoholic nanodispersions were prepared.The main research contents and innovations of this paper are as follows:(1)The saturated solubility of carbazole-based and oxadiazole-based organic small-molecule interface materials at different temperatures and in more than ten organic solvents were measured.Solubility-temperature relationships were correlated and appropriate models were fitted to expand the material solubility database.Based on the principle of "similar compatibility",combined with actual data,the selection range and rules of printing OLED ink materials in the conventional solvent orthogonal method were summarized.The results show that the dissolution behaviors of these organic small molecular materials with similar structures,which are mainly composed of a benzene ring plane conjugated structure and supplemented by heteroatoms such as nitrogen and oxygen,are highly similar.Printing OLED technology using solution as the transfer medium has a high demand for water or alcohol soluble materials and inks.(2)Based on the dissolution rule to guide the solvent collocation,uncoated and coated OLED organic small molecule nanoparticles were prepared by using the high-gravity enhanced antisolvent coupling technology,which expanded the selection range of ink solvents from the perspective of dissolution and dispersion.The optimal process conditions were N-methylpyrrolidone as solvent,water and monobasic saturated lower alcohol as antisolvent,the volume ratio between 40:(400～480)m L,and the supergravity level between 450 and 500.The particle size of four organic small molecule uncoated nanoparticles with characteristic structures of carbazole,oxadiazole,triphenylamine and anthracene was within 200 nm,and their saturated solubility in organic solvents such as acetonitrile and N-methylpyrrolidone was increased by more than 14%.Surfactants,which could modulate the surface tension of the ink,were added to further stabilize the coated composite nanoparticles.The composite nanoparticles with particle diameters of 16 nm and 100 nm were prepared,which were well dispersed in hydroalcohol and the availability was significantly improved.(3)Soluble luminescent polyfluorene derivatives with potential applications in printed OLEDs were selected as research objects.The high-gravity technique was used to overcome the amplification effect of uneven molecular chain growth during heterogeneous stepwise condensation polymerization based on the Suzuki cross-coupling reaction.A complete process route to meet the high temperature and oxygen-free requirements was developed.The process conditions were optimized and two polyfluorene derivatives with narrow molecular weight distribution were synthesized.The results showed that when the high-gravity level was 500 and the volume ratio of toluene to water was 1:3,the number average molecular weight of poly(9,9-dioctylfluorene)synthesized at 80 °C for 12 h was 18.5 k Da,and the polydispersity index was 2.06.The comprehensive performance of the printing blue OLED device with the product as the light-emitting layer was better than that of the product prepared by the thermal stirring method under the substrate equivalent.The poly(9,9-dioctylfluorene-alt-benzothiadiazole)synthesized under the same conditions for 24 h had a number average molecular weight of 35.2 k Da and a polydispersity index of 2.47.(4)Based on the dissolution rule of the soluble polyfluorene derivatives,uncoated luminescent polymer nanoparticles and their aqueous nanodispersions were prepared by high-gravity enhanced antisolvent coupling technology,providing a new idea for aqueous inks for printing OLED light emitting layers.The results show that the morphology and size of the two polymer nanoparticles obtained at the volume ratio of tetrahydrofuran and water at 30:480 m L and the high-gravity level at 500 were better,with a particle size of 190 nm and a polydispersity index of 0.14.The spherical nanoparticles retained the fluorescent properties brought by the conjugated skeleton of the molecular chain,while adding hydroxyl functional groups.The Zeta potential of the two aqueous nanodispersions with a solid content of 0.5% was below-35 m V,and they were stably dispersed in water for two months without sedimentation or agglomeration.