Study On Pixelation Of Quantum Dots Light-emitting Films And Their Electroluminescence Properties

In recent years,quantum dots light-emitting diodes（QLED）devices have made significant breakthroughs in performance and have promising applications in the display field.The preparation of pixelated quantum dots（QD）light-emitting diodes has been achieved through inkjet printing,UV exposure lithography and nanoimprinting.And the high-resolution QLEDs assembled with them have certain advantages in terms of display clarity and color reproduction.However,the degradation of QD photovoltaic performance and the lack of blocking between QD pixels,which results in high leakage currents due to direct shorting of electron and hole transport layers,have seriously hindered the improvement of the performance of high-resolution QLED devices.In order to solve the above critical issues,significant results have been achieved in high-resolution QLEDs by tailoring photo crosslinking ligands,optimizing dispersion solvents to enhance QD stability and using polymers to shield the direct contact between transport layers to reduce leakage currents.However,the above methods are generally only applicable to QDs with specific structures,and the direct use of polymers to cover the entire QD light-emitting film as an electron shielding layer will prevent electrons and holes from compounding in the QD emitting layer.Therefore,there is an urgent need to develop novel pixelation techniques for QD light-emitting films.Based on this background,this thesis innovatively proposes the pixelation of QD light-emitting films using an electrically driven strategy based on the advantages of electrically modulated self-assembly with high efficiency,stability and tunability,and assembles high-resolution QLED devices with excellent performance as the emitting layer of QLEDs.The main research of this paper is as follows:（1）Revealed the mechanism of electrostatic interaction to enhance the stability of QD light-emitting films:The poor stability of QDs limits their application in luminescent devices.In this section,we have developed a QD light-emitting film with excellent stability in terms of chemical and mechanical properties and a photoluminescence quantum yield（PLQY）of up to 96.1%by exploiting the electrostatic interactions between the C-F bonded electric dipole and the positively charged QD.In addition,backlight components assembled with this light-emitting films can enable LCDs to achieve more vivid and realistic color effects.（2）Constructed electrostatic induction strategy to prepare pixelated QD light-emitting films with high resolution:The conventional pixelated QD light-emitting films process suffers from problems such as damage to the optical and electrical properties of QDs.In this section,the preparation of pixelated QD light-emitting films with high resolution has been achieved by designing QD surface ligands to charge the QD surface and using electrostatic induction between the QD and the charged pattern.The designed scheme circumvents the damage of optical and electrical properties of QDs by photoresist,developer and electrically insulating cross-linked ligands during the preparation of QD pixels by conventional photolithography,and the pixel resolution is up to 3031 PPI.（3）Fabricated pixelated QD light-emitting films with ultra-high resolution by means of applied electric modulation:The preparation of ultra-high resolution pixels is one of the key development directions for future displays,however,existing pixel processes are still challenging in achieving ultra-high resolution pixels.This chapter proposes the self-assembly of QD pixels driven by an applied electric field,and one-dimensional array patterns with controllable line widths（from 45μm to 4.5μm）have been successfully prepared.And the electric field-induced QD localization deposition with spatially distributed intensity gradient variation was constructed by designing insulating substrate patterns within the electric field,and pixels with submicron size（0.6μm）in diameter were prepared to achieve ultra-high pixel resolution of 25000 PPI.（4）Avoided short-circuiting of electron and hole layers between pixels to produce low-leakage current high-resolution QLED:High-resolution QLED based on pixelated emitting layers has large leakage currents between pixels,which hinders devices performance.In this section,QD pixels have been prepared using electrostatic induction and electric field modulation,respectively,and the device leakage current has been reduced by constructing polymeric electron-blocking layers between the pixels.The above schemes simultaneously solved the problem of insulating polymers blocking electron transport between the pixels.Among them,the Cd Se QLED demonstrated excellent performance with an external quantum efficiency（EQE）of 15.6%and a maximum luminance of 22010 cd m^-2 at the pixel resolution of 1104 PPI,which is one of the most efficient QLEDs with QD pixel resolution over 1000 PPI.And this work greatly improved the transmittance of the QD emitting layer by constructing high-resolution QD pixels.Subsequently,optimization was performed on the transparent electrodes to screen the electrodes suitable for QLEDs.The resolution of the eventually assembled transparent QLED was 2116PPI and the transmittance was 90.7%,which represents the highest transmittance of transparent QLEDs so far.