Study On High Efficiency Organic Light Emitting Diode

Organic light-emitting diods(OLEDs)is a new light product which possesses the features of cleaning and pollution-free,high luminous efficiency and at the same time with flexible folding and others.Since the 1980 s OLEDs was first reported,after nearly three decades of research and development,OLEDs has developed from the laboratory to commercialization and industrialization.OLEDs has been widely used in lighting and flat panel display.Based on the interface physics and the structure of the OLEDs,this thesis started research though the mechanism of electron injection between carrier injection layer and the transport layer,therefore output the high efficiency monochromatic OLEDs.The relationship between the photoelectric characteristics of the device and the physical interface of the OLEDs is studied systematically.The author has made some innovative achievements in this research and understand the OLEDs interface physics deeper than before,hoping his research can provides some reference on development of new and high efficient OLEDs.The paper covers the following five aspects:The first chapter mainly introduces the structure of organic light-emitting diodes,luminous principle of organic light-emitting diodes,measurement of organic light-emitting diodes and other important parameters of the basic concepts.The author has deeper understanding on organic light-emitting devices by fabricate standard organic light-emitting device,thus making good basis to the following research.The second chapter mainly describes equipment and works principle of equipment required by the organic light-emitting diode fabrication process and OLEDs characterization.The fabrication process and operational process of organic light-emitting diode are described in detail.The thirdly chapter: The effect of indium trichloride buffer layer(InCl3)is as an injection layer in the indium tin oxide(ITO)anode between hole transport layer.A simple and efficient green organic light-emitting diode with simple structure and longlife was fabricated.It was found that the efficiency of the OLEDs was improved to a certain extent when we used conventional method of UV ozone cleaning to deal with the ITO anode,but not significantly.And when we spin coated the InCl3 aqueous solution on ITO anode as a layer of In Cl3 buffer layer film and a hole injection layer,this method not only improved the hole injection capacity,but also greatly improved the efficiency of the OLEDs,at the same time,we fabricated the high efficiency green light OLEDs.The whole process of spinning coated In Cl3 buffer layer film was exposed to the air environment.This method not only produces high efficiency OLEDs,but also greatly simplifies the experimental conditions.After the In Cl3 buffer layer is spin-coated on ITO anode,and when the luminance is 2000 cd/m2,the maximum electroluminescence efficiency of the OLEDs reachs 104.4 cd/A;the bright voltage is4.64 V,when the bright voltage of the traditional method is 5.63 V.When the luminance is 1000 cd/m2,the power efficiency of the OLEDs with spin-coated In Cl3 buff layer is63.61 lm/W,which is 87.1% higher than the 34 lm/W of the traditional method.When the luminance is 5000 cd/m2,the power efficiency of the OLEDs with spin-coated In Cl3 buff layer reachs 52.8 lm/W,compared with the power efficiency used the traditional method fabricated OLEDs of 14.51 lm/W which increased by 264.4%.By measuring the ultraviolet photoelectron spectroscopy and X-ray photoelectron spectroscopy properties of the ITO / InCl3 interface,it is found that the photoelectric performance of the OLEDs is improved because the work function of ITO is improved by spin-coating of In Cl3 buffer layer,which is equivalent to reducing the injection barrier.And it can improve the hole injection ability better than others.The fourth chapter manly studied the high efficiency organic light emitting diodes are fabricated when 8-hydroxyquinolinolato-lithium(Liq)used as electron injecting layer,1,3,5-Tris(1-phenyl-1H-benzimidazol-2-yl)benzene(TPBi),4,7-Diphenyl-1,10-phenanthroline(Bphen)and 8-hydroxyquinoline aluminum salt(Alq3)used as the electron transport layer.The transmission mechanism of electrons between the electron injection layer and the electron transport layer is investigated by measuring the photoelectric properties of the organic light emitting diodes.We used the material Bphen,TPBi,Alq3 as the electron transport layer,used Liq as the electronic injection layer to fabricate organic light-emitting diode,which were named as devices A,B,C.By measuring the photoelectric property of OLEDs,it was found that at the same voltage,the electroluminescent efficiency of device B is the largest,the electroluminescence efficiency of device A the second,the electroluminescenceefficiency of device C the smallest.The intensity of electroluminescence efficiency is consistent with the order of reduction of these three materials.At the same voltage,we fund that device A has the largest current density and brightness,and the current density and brightness of device B less than device A,and the current density and brightness of device C is minimal.The order of the current density and the brightness of the devices is as the same as the order of the electron mobility of the three materials.In the devices with different electron transport layer materials,when we analyzing the photoelectric properties of different devices,we found that Liq as the the electronic injection layer of a device,the device's photoelectric properties affected by two factors: that are the electronic transmission layer reduction strength;the electron mobility of the size in the transport layer material.In the fifth chapter the author summarized the work done at the graduate stage,hoping have a beautiful future in the further study of the Ph.D.