Research Of Inkjet Printed Quantum Dot Luminescent Materials And Devices

Quantum dot(QD)has exhibited attractive properties including sharp emission bandwidth,size-dependent emission wavelength,solution processability,and high emission efficiency.For QDs materials,inkjet printing is a promising deposition technology,which is capable for large area fabrication and mask-free patterning.It is very suitable for the fabrication of next-generation optoelectronic devices.However,there are still many challenges in achieving the high efficiency and stability of the printed device.In view of the instability of inkjet printed perovskite photoluminescent material and the unsatisfactory performance of quantum dot light-emitting diode(QLED),the following four parts are studied in my project:(1)In this work,quasi-2D perovskites embedded in different polymers are prepared by inkjet printing,which also enables us to construct any luminescent patterns/pictures on the polymer substrates.The optimized quantum yield reaches over65%by polyvinylchloride based quasi-2D perovskite composites.In addition,as-fabricated perovskite-polymer composites with patterns show excellent resistance to abrasion,moisture,light irradiation,and chemical erosion by various solvents.Both quantum yield and lifetime are superior to those reported to date.These achievements are attributed to the introduction of the PEA⁺cations to improve the luminance and stability of perovskite.(2)This work,therefore,redesigned the annealing process of the hole transport layer to achieve an optimized smooth surface with a reduced number of defects for ink-jet printed QLEDs.Optimized morphology brings back a maximum luminance of over30000 cd/m² and external quantum efficiency of 7.52%for the inkjet printed red QLED based on Cd Se QDs.Moreover,the operation lifetime of the ink-jet printed device is also enhanced by the restored surface morphology.An enhanced T50 lifetime of the ink-jet printed device at 1000 cd/m² is improved from 26 h to 127 h,which converted to a long T₅₀ lifetime of 8013 h,when operated at 100 cd/m².(3)A ternary ink system consisting of octane,cyclohexyl ethanol and n-butyl acetate was developed,which solved the erosion between the printed quantum dot ink and the hole transport layer below.In addition,gradient vacuum pressure(GVP)was used to post-treat the ternary ink system to obtain uniform quantum dot layer.Based on these two technologies,inkjet printed QLED with high efficiency,long life and high resolution was prepared.The external quantum efficiency of R/G/B devices showed19.3%,18.0%,and 4.4%,respectively.Under the initial brightness of 1000 cd/m²,the half operating lifetime(T₅₀)was up to 25178h and 20655h for red and green devices.For blue device,the lifetime showed 46 h@100 cd/m².The improvements in ink engineering and post-processing in this study have improved the efficiency and stability of the device to a higher level,confirming the application prospect of printed QLED in the display industry.(4)In this work,the thickness of the outermost Zn S shell of green QDS is controlled.When the outermost Zn S shell is 7 atomic layers,the QD shows the optimal PQLY and fluorescence lifetime.It is proved that the appropriate Zn S shell can improve the exciton radiation efficiency and inhibit the associated non-radiative recombination.Green QLED was prepared by inkjet printing using quantum dots with different shell thickness.The results show that the QLED based on the optimal quantum dot preparation also shows excellent electrical performance,with an EQE of more than20%and a T₅₀ lifetime of more than 27000 hours at an initial brightness of 1000cd/m².The single-carrier devices and capacitance-voltage test results shows that the improved performance of QLED is due to an appropriate shell thickness that improves the balance of carrier injection and thus inhibits the radiation-free process of inkjet printing devices.