Study On Physical Properties Of Doped Organic Optoelectronic Devices

Organic light-emitting diode(OLED)is the most popular display technology,which has advantages of high efficiency,color healthy and flexible at the same time.OLED has been successfully used in flat panel displays and solid state-lighting.However,the industrial application of organic light-emitting diodes is still limited by the problems of lifetime and efficiency.This paper attempts to use doping technology to improve the performance of OLED devices.The specific principles of the doping in the transport layer and the doping in the light-emitting layer are investigated.Our study is quite meaningful for the realization of high efficiency and long lifetime in the practical application of OLED devices.The research contents of this thesis are as follows:In Chapter 1:The background of OLED,the development history of OLED,the advantages and disadvantages of OLED,and the applications of OLED are introduced.Finally,the specific research questions of this paper,as well as the feasibility of research questions are discussed.In Chapter 2:From the aspects of OLED device structure,OLED classification,OLED principle,as well as the performance parameters of OLED,the OLED knowledge is introduced.This can provide theoretical guidance for the subsequent discussion of the article.In Chapter 3:The doping properties of the hole-transporting layer are studied.The strong organic electron acceptor material 1,4,5,8,9,11-hexaazatriphenylene-hexacarbonitrile(HATCN)and inorganic materials MoO3 have completely different doping mechanism.Unlike NPB:MoO3,there is no p-type doping effect based on NPB:HATCN hole-transporting layer.The diffusion of HATCN small molecule and the modification effect of ITO interface make the device an improved performance.Then the interfacial diffusion effect of HATCN molecules is measured.In Chapter 4:Studies of Chapter 3 have proved that NPB:MoO3 is a good p-type doped hole-transporting layer,so we try to apply it in OLED devices.A p-type doped layer is inserted between the n-type doped electron-injecting layer and the cathode to form a new p-i-n-p structure.Compared with the conventional p-i-n-based devices,the performance of the device(p-i-n-p structure)has been significantly improved.After investigation,we found that the improvement of device performance is mainly due to the improved electrical conductivity,enhanced thermal stability and protection of the electron-injecting layer.In Chapter 5:The effect of doping of the light-emitting layer on the device is studied.A new comparative study of the hosts based on dibenzofuran/spirobifluorene and the common commercial CBP is conducted.With the use of new host material,the device has a 1.5 times longer lifetime.We further investigate the growth of dark spots,the film's crystallization properties and recombination zone to discover the reason behind the improved performance.It is believed that a higher glass transition temperature can effectively inhibit the crystallization of the film when the device is operating;more importantly,the wider charge recombination zone can further enhance the stability of the device.In Chapter 6:The application of the host with narrow band gap in blue phosphorescent organic light emitting diodes is investigated.A new host material,2,8-bis(9,9-dimethylacridin-10(9H)-yl)dibenzo[b,d]furan(DBF-DMS)is synthesized and used as the host.The blue phosphorescent organic light emitting diode can achieve an external quantum efficiency of 26.6%.The increased carrier injection and transport ability and improved stability of the new material DBF-DMS make the device a lower driving voltage and a longer lifetime.After further device structure optimization,a device lifetime of more than 100 hours is obtained.The host material with narrow bandgap and high triplet energy such as DBF-DMS can be successfully used in the application of high performance blue phosphorescent organic light emitting diode devices.Finally,we achieve a blue phosphorescent OLED device with high efficiency and long lifetime.In Chapter 7:The full text is summarized tand the final conclusion is made.In summary,this study is focused on the problem of doping in OLED device.Some differences between the organic and inorganic materials doped with the hole-transporting layer are clarified,and the misunderstanding is eliminated.A p-type doping transport layer is successfully used in the special field to prepare the OLED device with a p-i-n-p structure.The important effect of the host material on the doped light-emitting layer is understood.The blue phosphorescent OLED device with high efficiency and long lifetime is realized by synthesizing and using the appropriate host material.This paper studies the application of doping technology in OLED,and provides the technical reserve for realizing the industrialization process of OLED.