Blue Organic Light-Emitting Device and the Study of the Mixed-Host Emitting Layer

• Main Authors: Tien-Chun Lin, 林典群
• Other Authors: Jiun-Haw Lee
• Format: Others
• Language: en_US
• Published: 2005
• Online Access: http://ndltd.ncl.edu.tw/handle/74306347735731022186

碩士 === 國立臺灣大學 === 光電工程學研究所 === 93 === In this thesis, we report a blue organic light emitting diode (OLED) whose emitting layer is 9,10-di(2-naphthyl)anthracene (ADN) doped with 4,4''-bis[2-(4-(N,N-diphenylamino)phenyl)vinyl]biphenyl (DPAVBi). The efficiency improvement of this device compared with others is attributed to the use of high electron mobility material bis(10-hydroxybenzo[h]qinolinato) beryllium (Bebq2) as the electron transport layer such that a better carrier balance can be achieved. From transient electroluminescence (TREL) measurements of the blue devices, we also confirmed that the DPAVBi dopant in the ADN blue emitting host does not affect the electrical property too much. When the dopant concentration is changed from 2% to 4%, a highest current efficiency of 16.4 cd/A is measured under the condition of a current density of 20 mA/cm2 at a driving voltage of 4.9 V. In the study of mixed layer (NPB:Alq3) OLED, heterojunction and mixed layer devices were fabricated, where NPB represents N,N -Bis(naphthalen-1-yl)- N,N-bis(phenyl)benzidine and Alq3 represents tris(8-hydroxyquinoline) aluminum. By comparing the spectral shift of electroluminescence between heterojunction and mixed host OLEDs, the recombination zone positions with different mixing concentrations have been determined. The results show that the recombination zone shifts from the anode to the cathode side with increasing the mixed ratio of NPB. An optical simulation program was used to model its optical characteristics. We found that when the NPB:Alq3 mixed ratio is equal to 1:3, 1:1, and 3:1, the major recombination position is at 500, 600, 700 A away from the ITO anode, respectively..