The Structural Design And Application Of Non-doped Charge Generation Layer On Tandem Organic Light-emitting Diodes

Tandem organic light-emitting diodes (TOLED) consist of vertically stacked two ormultiple light-emitting units connected by charge generation layer, under an applied electricfield, the charge generation layer supplies electrons and holes to composite with holes andelectrons from anode and cathode in the emitting layers, respectively, thus achieving highluminance and efficiency. In contrast to the traditional single-unit OLED, tandem OLED haveadvantages of enhanced current efficiency and luminance at low current density, as well asprolonged lifetime. Even though the study of charge generation layer has achieved greatprogress, some problems still existed, for example, doping process inevitably complicates thefabrication process; the high evaporation temperatures has effect on the performance oftandem OLED. Therefore, in the paper we mainly aimed to design efficient charge generationlayer to achieve great performance tandem OLED. The details are as follows：1. LiF/Al/C60/m-MTDATA was fabricated as CGL. Firstly, we verified the generation ofcharge on C60/m-MTDATA interface, and inferred the process of charge generation. Besides,through a series of inversion devices, we optimized the thickness and evaporation rate of CGL,then achieved the thickness of Al and C60are both7nm, respectively, and the evaporationrate of Al is1/s. Lastly, we fabricated tandem OLED based on optimized CGL, andcompared with single-unit OLED and TOLED based on LiF(1nm)/Al(7nm)/CuPc(7nm)/m-MTDATA(10nm) as CGL, then the maximum current efficiency and powerefficiency of TOLED were48.1cd/A,19.3lm/W, respectively, which were2.98,1.65times higher than that of single-unit OLED, and1.2,1.13times compared with that of anotherTOLED.2. We used LiF/Al/HAT-CN/m-MTDATA as CGL to fabricate TOLED with NPB/Alq3as emitting unit. The CGL consists of HAT-CN with low evaporation temperatures, and hasmore than90%transmittance during the whole visible region, thus showing greatperformance for generating and separating charge. Then it was found that the thicknessinfluenced the generation and separation of CGL through regulating the thickness of HAT-CNand Al, so the thickness of HAT-CN and Al were determined to be9nm,5nm, respectively.Compared with the stack device and single-unit device, the maximum current efficiency andpower efficiency of TOLED were4.84cd/A,1.79lm/W, which were2.2,1.6times than thatof single-unit device, respectively.3. Ag was applied to CGL consisting of LiF/Ag/HAT-CN/m-MTDATA. Ag, which notonly has great electrical conductivity, but also shows the LSPR that is to absorb the visiblelight when the thickness of Ag is1-2nm. The TOLED were fabricated with differentthickness of Ag, then when Ag was1nm, the maximum current efficiency of TOLED was upto6.76cd/A,2.7times than that of single-unit device. Moreover, we fabricated the blueTOLED with LiF/Al/C60/m-MTDATA, LiF/Al/HAT-CN/m-MTDATA, LiF/Ag/HAT-CN/m-MTDATA as CGL, three TOLED have different characters, which supply another choicefor the fabrication of TOLED with different performance in future.