Controlled Assembly Of Organic Micro/Nanocrystals By Dip-Coating Method And Their Applications In Optoelectronic Devices

Organic micro/nanocrystals have higher carrier mobility and longer exciton diffusion length,and their photoelectric properties are significantly better than the corresponding amorphous thin film system,which have become a hotspot in the field of organic semiconductor materials.In this thesis,large-area assembly of organic micro/nanocrystals has been achieved via a simple dip-coating method.We further investigated the detailed parameters that could greatly affect the assembly process such as the pulling rate,solution concentration,and substrate tilting angle.The application of the ordered organic micro/nanocrystals on photodetectors and light-emitting diodes(LEDs)were investigated.These results are summarized as follows:1.Patterning of organic micro/nanocrystals via dip-coating method and their applications in photodetectors2,5,8,11-tetra-tert-butylpelene(TBPe)organic polyhedral crystals with a size of 0.8-3.5?m were synthesized by surfactant-assisted method,then the photolithography-assisted dip-coating method was utilized to position these organic micro/nanocrystals in the photoresist holes,with the patterning yield up to 90%.We further detailed investigated three important factors that possibly affected the patterning effect,such as the pulling rate,solution concentration,and the tilting angle of the substrate.The pulling speed of 0.8?m/s,a concentration of 0.15 mg/mL and the angle of 15° were found to be the optimal parameters in our experiments.At the same time,by changing the photoresist patterns,we can achieve TBPe crystals with ring,round,cross-shaped arrangement.The number of TBPe crystals in each photoresist hole can be precisely controlled by changing the ratio between the diameters of TBPe crystals and the dimensions of photoresist holes,and this method is highly versatile and suitable for the patterning of a variety of organic micro/nanocrystals,such as two-dimensional microsheets of C60,7,7,8,8-Tetracyanoquinodimethane(TCNQ)and tris(8-hydroxyquinoline)aluminum(Alq3).The photodetector based on patterned C60 microsheet shows excellent and stable photoresponse with a high on-off ratio of 100.The dip-coating method we proposed is simple and versatile,and it has great potential in the construction of large-scale high-performance functional integrated organic micro/nanocrystals based devices.2.Assembly uniform film of organic-inorganic hybrid perovskite quantum dots by dip-coating method and their application in light-emitting diodesThe uniform organic and inorganic hybrid perovskite quantum dots(?4.2 nm)were prepared by solvent exchange method,by adopting a simple dip-coating method,large-area uniform films of organic-inorganic hybrid perovskites quantum dots(HP-QDs)were effectively fabricated.Using this technique,we successfully fabricated multicolor QDs solution emitting in blue,blue-green,green,orange to red color by simply changing the halide composition or size of HP-QD.The film thickness can be tuned by adjusting the pulling speed.Based on the HP-QDs films,we successfully fabricated multicolor HP-QDs LEDs emitting in blue,blue-green,green,orange to red color.A maximum current efficiency of 3.72 cd/A and external quantum efficiency of 1.06%are achieved at a luminance of 2398 cd m-2.Furthermore,the packaged QD-LEDs remain stable in air of 50%humidity for at least 7 d.The work demonstrates the great potential of the dip-coating method to fabricate large-area uniform films for various QDs,and also demonstrates the promising potential of HP-QDs for photovoltaic cells and photodetectors.