Effect Of Organic Composite Hole Transport Layer On Performance Of Quantum Dot Light-emitting Diodes

With the increasing attention paid to environmental and energy issues,the preparation of high efficiency,long life and low energy consumption light-emitting devices has become one of the biggest goals of relevant scientific researchers and industry.Quantum dot light-emitting diodes（QLEDs）have attracted extensive attention due to their merits such as adjustable wavelength,high color purity and low energy consumption,which have great application prospects in the field of lighting and display.Although QLEDs have shown considerable commercial prospects,the device performance is far from reaching the level of practical application,and the working mechanism of the device and factors affecting the device performance need further study.This thesis focuses on the influence of the transport layer on the device performance.By designing and optimizing the composite hole transport layer,a series of red QLEDs device with high efficiency were successfully prepared,and the working mechanisms were analyzed in depth.The detailed work is as follows:（1）The electron transport characteristics of TPBi thin films with different thickness（150～260 nm）were studied by using current-voltage characteristics and admittance method.The electron mobility of TPBi films with different thickness measured by admittance method is 5.6×10^-8～2.1×10^-5 cm² V^-1s^-1,which is much lower than those of the electron transporting materials Tm Py PB and Bm Py PB.The performances of the red organic light emitting diodes based on TPBi,Tm Py PB and Bm Py PB as the corresponding electron transfer layers（ETLs）were also investigated.The results show that the performance of the TPBi ETL device is obviously inferior to those of the other two devices.In addition,the reason for the performance differences is examined through the analysis of the working mechanisms of the devices.（2）A series of red quantum-dot light-emitting diodes（QLEDs）are developed using PVK mixed TAPC as hole transport layer（HTL）by all-solution processing.The current density-voltage characteristics of carrier-only devices shows that the PVK:TAPC composite HTL exhibits the increase of current density at the same voltage with increasing the mixing concentration of TAPC.And the hole and electron currents are almost identical as the mixing concentration of TAPC is equal to 20%.The corresponding red QLED achieves the highest performance with a maximum luminance of 289490 cd m^-2,a maximum CE of 26.8 cd A^-1,a maximum EQE of 17.9%.The T₅₀ lifetime is up to 65 min,which is more than 8 times longer than that of QLED with PVK as HTL at an initial luminance of 100000 cd m^-2.Even at a very high brightness over 50 000 cd m^-2,the QLEDs can still maintain a high CE of 26.6 cd A^-1and an EQE of 17.4%,showing much lower efficiency roll-off.