Study On The Device Stability Of Quantum Dot Photoluminescence And Electroluminescence Devices

Due to the advantages of high luminous efficiency,precise tuning and narrow emission spectra,quantum dots(QDs)are an ideal candidate for displays and TVs with high saturation color and wide gamut,which have an excellent application prospect.At present,the main factor restricting the commercialization of quantum dot display technology is the stability of devices.Therefore,the thesis starts with the cause of the aging of quantum dot devices and studies their lifetime,so as to improve the stability of devices.The stability of the QDs is mainly influenced by oxygen and temperature,herein,we use double-layer glasses to pre-encapsulate quantum dot materials,and investigated the effects of chip scale package(CSP)and surface mounted devices(SMD)packaging methods on device stability.Through the design of pre-encapsulation and multi-layer isolation of water and oxygen,the influence of water and oxygen on the photoelectric performance of quantum dots is reduced.At the same low current of 10 m A,the photoelectric performance of devices with CSP structure tends to be stable after aging for200 h at 85?and 85%humidity,but the luminous maintenance rate is less than 85%.Since the distance between the chip and the quantum dot is increased and the influence of chip heating on the quantum dot is reduced,the luminous maintenance rate of the device packaged with the SMD structure can still reach 88.16%after 1000 hours of aging.In addition,the color offset of device is(0.024,0.012),and the maintenance rate of the red and green luminous peak is about 74%and 79%,which is greatly improved compared with the traditional packaging structure.In quantum dot light emitting diodes(QLEDs),the electron transport material and the interface were optimized to improve the device stability.Red QLEDs are fabricated by all-solution method.Zn O nanoparticles,Zn O precursor and Zn Mg O were used as electron transport materials to fabricate QLEDs respectively,and their thicknesses were optimized.The best performance of the QLEDs is obtained when the electron transport layer is Zn Mg O of 45 nm.The maximum brightness of the device is 266,670 cd/m~2,the maximum external quantum efficiency reaches 14%,and the lifetime of the device can reach 13.9 h after encapsulating and constant current aging.To inhibit the charge transfer between the emitting layer and the electron transport layer,the insulating polymer,polymethyl methacrylate(PMMA),is inserted between QDs and Zn Mg O.By measuring the time-resolved spectra and conducting the constant current aging of devices with the initial brightness of 1000 cd/m~2,it can be found that the insertion of PMMA with different thickness has different effects on the lifetime of QLEDs.With the increase of PMMA thickness,the charge transfer at the interface between quantum dot and Zn Mg O decreases,which increases the lifetime of exciton.Meanwhile,the charge accumulation in the electron transport layer decreases,which increases the device lifetime.By inserting PMMA of suitable thickness,the device lifetime is increased from 13.9 h to 28.7 h.