Structure Optimization And Performance Study Of QLED Device Based On CdSSe Quantum Dots

Core-shell structure quantum dot(QD)which based on solution preparation has unique properties: compared with the organic luminescent material,it has the characteristics of good water and oxygen stability,high luminous color purity,high luminous efficiency,emission spectrum can be regulated with the quantum dot size and other characteristics,it has become a hot research field in flat panel display industry in recent years.Quantum dot lightemitting diodes(QLED)with quantum dots film as light emitting layers have lower power consumption,longer life,and lower manufacturing costs than organic light emitting diodes(OLED),promising to be the next generation of flat panel display technology.Although QLED display technology has a broad prospect in solid-state lighting and display,however,due to the current research is still in the initial stage,many performance issues need to be resolved,such as: the low luminous efficiency,non-ideal brightness,the short life,therefore,the subject of improving the performance of quantum dot light emitting diodes is worth studying and challenging.This article is mainly through the following means to improve the brightness and efficiency of devices.The specific research contents are as follows:(1)Firstly,the film transmittance of nano ZnMgO and nano ZnO were tested and the surface morphology of the films were observed under atomic force microscope.Secondly,nano ZnMgO and nano Zn O were used as the electron transport layers,and the quantum dot light emitting devices(a: ITO/PEDOT: PSS/PVK/QD/ZnO/Al,b: ITO/PEDOT: PSS/PVK/QD/ZnMgO/Al)were prepared by the whole solution method.The effects of nano ZnMgO and nano ZnO on the QLED devices were analyzed by measuring the current-voltage-luminance-luminescence spectra of the two devices.The results show that: the nano ZnMgO has a higher electron mobility than that of nano ZnO and the energy band between quantum dots is lower,which can make the electrons inject more efficiently,therefore,the performance of nano ZnMgO devices is better than that of nano ZnO devices.The nano ZnMgO device brightness up to 1722 cd/m~2,turn on voltage is 1.9 V,current efficiency is 4.36 cd/A,and the device's withstand voltage is stronger,the breakdown of the device occurs at 9 V.(2)The process conditions of the preparation of the luminescent layer in the QLED affect the performance and stability of the device,therefore,we explore and optimize it.Firstly,the effects of the thickness of the quantum dots on the morphology and the photoelectric properties of the devices were systematically analyzed.The results show that: the quantum dots are agglomerated when the quantum dot layer was too thick,and the aggregation phenomenon was weakened with the decrease of thickness;when the quantum dot layer thickness and quantum dot size were equivalent(about 10 nm),the quantum dots were arranged in a single layer and the aggregation phenomenon disappeared;when the thickness of the quantum dot layer was below 10 nm,the film was defected with holes.The experimental results showed that the thickness of quantum dot layer in QDs was closely related to the photoelectric properties of the devices.Optoelectronic properties of the device with the quantum dot layer thickness of 10 nm were the best: it had the lowest turn on voltage of 2.1 V,the highest brightness of 1782 cd / m~2.Secondly,the effects of annealing temperature on the QD-LEDs and the quantum dots during the preparation of quantum dots films were analyzed.Atomic force and thermo gravimetric analysis show that: the surface roughness of quantum dots film does not change at different annealing temperatures,the heat treatment has no effect on the morphology of the films;when the temperature rises from 120 ? to 160 ?,the weight of quantum dots continues to decrease;when the annealing temperature is 160 ?,the device has the highest performance: it had the lowest turn on voltage of 2.0 V,the highest brightness of 1622 cd / m~2,due to the large amount of ligand shedding,the weight of quantum dot decreases rapidly and the quantum yield of quantum dots decreases,so the performance of the device is reduced.(3)As the basic device structure used in the experiment is electronic device which is of electronic dominance.We can improve the device performance by increasing the hole injection capability and by using a methanol solution to treat the PEDOT: PSS film.Atomic force microscopy test results show that: methanol-treated PEDOT: PSS film can reduce its surface roughness and make the film surface smoother.The analysis of X-ray Photoelectron Spectroscopy of Thin Films shows that: after the methanol treated the film,the insulating PSS was separated from the PEDOT polymer,the reduction of PSS improves the conductivity of the film,and the hole injection capacity is enhanced,Methanol-treated device performance which related to the untreated device has greatly improved with the brightness increased by 30 %.