A Study of Blue Organic Light Emitting Diodes with Bipolar Transport Layers

• Main Authors: Chien-Ci Chu, 朱健慈
• Other Authors: Meiso Yokoyama
• Format: Others
• Language: en_US
• Published: 2002
• Online Access: http://ndltd.ncl.edu.tw/handle/00817251919062771324

碩士 === 義守大學 === 電子工程學系 === 90 === In this study, we could reduce the holes accumulated in the interface and enhance electrons injection into emission layer by using bipolar transport emission layer (BTEL). The structure of BTEL OLEDs is ITO/NPB/BTEL(NPB:CuPc)/BCP/Alq3/Al. ITO is used as an anode and NPB、BTEL、 BCP、Alq3、Al are used as a hole transport layer (HTL), an emission layer (EML), a hole blocking layer (HBL), a electron transport layer (ETL), and a cathode, respectively. The BTEL layer consists of NPB and CuPc, and is prepared with co-evaporation. This structure could enhance the electrons injection into the emission layer to balance the amount of holes and electrons, and reduce the hole accumulation in the EMT/HBL interface. First, We investigate the characteristics of BTEL OLEDs with various ratio and thickness in BTEL layer. Experimental results show that a BTEL OLED with the structure of ITO/NPB(10nm)/BTEL(20nm)/BCP(15nm)/ Alq3 (25nm)/Al[NPB:CuPc=10:1] exhibits good optoelectrical characteristics. The lifetime of an OLED with BTEL is three times than without BTEL, and the brightness is improved by two times. Secondly, NPB/CuPc mult-layer is used in OLEDs structure to separate the holes in the EML/HBL interface. The structure of multiple-quantum-well (MQW) OLEDs is ITO/(NPB/CuPc)n/NPB/BCP/Alq3/Al. n is varied from 0 to 6. Varying the thickness ratio of NPB and CuPc, and investigation the characteristics of MQW OLEDs. The optimum structure is ITO/[NPB(5.4nm)/CuPc(0.75nm)]4 /NPB(5.4nm) /BCP(15nm)/Alq3(25nm)/Al(200nm), The brightness and efficiency of an OLED with a MQW structure is two times than without MQW. The structure of MQW could balance the amount of holes and electrons in the emission layer to improve luminance efficiency. Obviously, there are rather improvements of blue organic light emitting diodes performance by using either bipolar transport emission layer, or NPB/CuPc multiple-quantum-well structures.