Study Of Photoelectric Properties On Tandem Blue Organic Light-emitting Devices Based On Firpic

Tandem organic light-emitting diode is a novel structure with high luminance,long lifetime and high stability,et al.In order to improve the performance of blue organic light emitting diodes?OLEDs?and solve the problem of low efficiency of blue OLEDs,the following research is carried out in the thesis:First of all,the research of C₆₀/Pentacene as charge generation layer is carried out,and the design and optimization of the basic structure of tandem device are completed.In order to solve the problem of low performance for using C₆₀/Pentacene as charge generation layer alone,buffer layer Cs₂CO₃/Al is added to modify charge generation layer,and a series of tandem OLEDs based on Cs₂CO₃/Al/C₆₀/Pentacene as charge generation layer have been fabricated and investigated.The experimental results show that the maximum current efficiency of 1.43 cd·A^-11 is achieved for Tandem OLED under the current density of 30 mA·cm^-22 after Cs₂CO₃/Al buffer was added,and it achieved a 29%increase over single-unit device(1.11 cd·A^-1).It is indicated that Cs₂CO₃/Al as buffer layer can improve charges'abilities of injection and transport.Next,the performance of blue tandem phosphorescent devices with various doping concentrations are investigated.The experimental results show that the performance of tandem devices with 5%and 15%doping concentrations are reduced by insufficient energy transfer under a low concentration and intensification of quenching under a high concentration.The performance of tandem device with 10%doping concentrations is relatively high,and a maximum current efficiency of 3.41 cd·A^-11 can be achieved.Then,in order to further improve the performance,the blue tandem devices are optimized by changing the material of electron transport layers.The results found that a current efficiency of 3.96 cd·A^-11 can be reached under the brightness of 163 cd·m^-22 when BCP is used as electron transport layer.It is proved that holes can be effectively blocked due to BCP's high HOMO energy level.And a current efficiency of 3.0 cd·A^-11 can be maintained within the brightness of 1000 cd·m^-22 when Alq₃ is used as the electron transport layer.It is proved that Alq₃ is still one of relatively stable electron transport materials for blue tandem OLEDs.Although TPBi has a high electron mobility,it is not suitable for the structure due to the mismatching of energy level,and its maximum current efficiency is only 1.80 cd·A^-1.Finally,to solve the problems of internal unbalanced carriers,low power efficiency and impure chromaticity of tandem devices,BCP is added in tandem structure as hole blocking layer.Experimental results show that the maximum current efficiency and the maximum power efficiency of tandem devices can be respectively reached 8.55 cd·A^-1and 0.89 lm·W^-11 after two hole blocking layers added,which are respectively increased by151%and 123%over the device without hole blocking layer(3.41 cd·A^-11 and 0.40lm·W^-1).And the CIE coordinate eventually reaches?0.167 0.094?.It is indicated that this tandem structure can not only improve the efficiency of blue devices,but also solve the problem of impure chromaticity.