Font Size: a A A

Study On Optoelectronic Performance Of Tandem Phosphorescent Organic Light-emitting Diode With Undoped Charge Generation Layer

Posted on:2019-07-12Degree:MasterType:Thesis
Country:ChinaCandidate:F LiuFull Text:PDF
GTID:2428330590465895Subject:Integrated circuit engineering
Abstract/Summary:PDF Full Text Request
Organic Light-Emitting Devices?OLEDs?have great application value and development prospects in the field of flat-panel display and solid-state lighting owing to flexibility,wide viewing angle,high brightness,rich colors,high pixel,low consumption,etc.Compared with the traditional OLEDs,the tandem OLEDs are devices that formed by charge generation layer?CGL?connecting several independent light-emitting units.On the one hand,carrier migration and recombination are not affected by the position of the light-emitting unit.On the other hand,the current efficiency of the tandem OLEDs is multiplied and the lifetime is longer than the traditional OLEDs.In this paper,we first studied the effect of non-doped organic CGL on the photoelectric properties of tandem OLEDs.Then we studied the blue phosphorescent OLEDs with traditional structure and fabricated a tandem white OLEDs based on non-doped inorganic CGL through combining blue light-emitting unit with red unit.Finally,the effect of changing the thickness of functional layer in CGL on the optoelectronic properties of white OLEDs was studied.The main research content includes the following three parts:First,Al and MoO3 buffer-modified organic heterojunction C60/pentanece was designed as CGL,and Al and MoO3 were used as the electron and hole injection layers of C60/pentacene CGL,respectively.The results show that inserted Al and MoO3 can effectively increase the charge injection capacity of organic CGL,resulting the improvement of luminance and current efficiency of tandem OLEDs.The turn-on voltage of tandem OLEDs is much lower than that of single-unit device and the current efficiency is more than 2 times as the single-unit device.Tandem OLEDs can exhibit excellent photoelectric performance when the thickness of Al/C60/pentanece/MoO3 is3/15/25/1 nm.The maximum luminance and current efficiency are 7920.0 cd/m2 and16.4 cd/A,respectively.Second,blue OLEDs with excellent performance is the key to achieving efficient tandem white OLEDs with red and blue light-emitting unit.We designed and fabricated phosphor-doped host-guest structure OLEDs,and the blue-ray iridium complex electrophosphorescent material FIrpic acts as object material.Properties of the devices can accommodate by changing the host materials,dopant concentration and thickness of the light-emitting layer.FIrpic is doped in four host materials:TCTA,TPBi,mCP and TmPyPB and the study shows that the host material mCP has a higher triplet excited state energy level,which can effectively prevent FIrpic triplet excited state energy backtracking to host material,thus a higher luminous efficiency.When mCP is selected as the host material,the thickness of the light-emitting layer is 30 nm and the dopant concentration is 8 wt%,the excitons can be effectively confined in the light-emitting region.As a result,the maximum brightness and the maximum current efficiency of the blue device can achieve 7196.3 cd/m2 and 15.5 cd/A,respectively.Third,an inorganic CGL with structure of Cs2CO3/Al/MoO3 was designed.Tandem white OLEDs based on this CGL was fabricated by using red light-emitting layer TCTA:Ir?piq?2?acac?and blue light-emitting layer mCP:FIrpic.The effect of the thickness variation of Cs2CO3 and Al on the photoelectricity properties of tandem white OLEDs was studied.The results show that the current density of tandem OLEDs increases with the increase of the thickness of Cs2CO3 and then decreases sharply when the thickness of Cs2CO3 is more than 0.8 nm.This is because thin Cs2CO3 can be used as electron injection layer of CGL,which can improve electron injection,but when the thickness increase Cs2CO3 layer change into an insulating layer.When the thickness of Cs2CO3 is 0.8 nm,the maximum brightness and current efficiency of the device are7120 cd/m2 and 7.1 cd/A,respectively.For the conductive material Al,electrons can be easily transferred from the Lowest Unoccupied Molecular Orbital?LUMO?of MoO3 to the LUMO of Al.The electrons injection ability of the CGL is optimized by changing the thickness of the Al layer,which can balance the electrons and holes concentrations in the light-emitting layer.The results show that when the Al thickness is 5 nm,the maximum brightness and maximum current efficiency of the device are 7890 cd/m2 and7.8 cd/A,respectively.
Keywords/Search Tags:Non-doped charge generation layer, tandem, blue phosphorescent device, photoelectric property
PDF Full Text Request
Related items