Efficiency Enhancement of Organic Light-emitting Diodes by Exciplex Sensitized Triplet-triplet Annihilation for Blue Emission and Different Thermally Activated Delayed Fluorescence Emitters

• Main Authors: Po-Chen Tseng, 曾柏宸
• Other Authors: 李君浩
• Format: Others
• Language: en_US
• Published: 2017
• Online Access: http://ndltd.ncl.edu.tw/handle/ez6y2p

碩士 === 國立臺灣大學 === 光電工程學研究所 === 105 === There are two topics in this thesis. The first one is efficiency enhancement of exciplex sensitized triplet-triplet annihilation (ESTTA) blue organic light emitting diodes (OLEDs). The second one is red, green, blue OLEDs with 9,9''-(2-(1-Phenyl-1H-benzo[d]imidazol-2-yl)-1,3-phenylene)bis(9H-carbazole) (o-DiCbzBz) as the universal host material for thermally activated delayed fluorescence (TADF) emitters. The exciplex was formed at interface of electron donor and acceptor organic materials, then triplet energy transfer (TET) to TTA blue emitter to generate upconversion blue emission, which was called exciplex sensitized triplet-triplet annihilation (ESTTA) process. With insertion of triplet assisting and singlet blocking (TASB) layer and incorporation of fluorescent dopant, the blue ESTTA-OLED exhibited maximum external quantum efficiency (EQE) of 5.1% including blue emission EQE of 3.8%. In addition, transient electroluminescence (TrEL) was used to examine the origin of blue emission. In turn-off luminance response, only slow decay was observed implying blue emission all came from exciplex energy transfer to emitter to facilitate TTA upconversion emission, called ESTTA process. o-DiCbzBz was used as host material, doped with metal-free red, green, and blue TADF dopants to achieve high efficiency OLEDs in order to simplify manufacturing process and reduce production cost. After the optimization of the device structure, maximum current efficiency of 11.3 cd/A, 91.8 cd/A, and 31.4 cd/A, maximum power efficiency of 11.9 lm/W, 91.9 lm/W, and 28.2 lm/W, and maximum EQE of 9.0%, 26.2%, and 11.5% were obtained for blue, green, and red TADF-OLEDs, respectively, showing the feasibility of o-DiCbzBz as the universal host for RGB high efficiency TADF-OLEDs.