Investigation of High efficiency Organic Light- Emitting Diodesby using Thermally Activated Delayed Fluorescence Materals

• Main Authors: Cheng-Yu Lu, 呂承育
• Other Authors: Chih-Hao Chang
• Format: Others
• Language: zh-TW
• Published: 2016
• Online Access: http://ndltd.ncl.edu.tw/handle/g6c9r3

碩士 === 元智大學 === 光電工程學系 === 104 === In principle, a phosphorescent emitter can use both singlet and triplet excitons, leading that organic light-emitting diodes (OLEDs) with phosphorescent emitter renders an internal quantum efficiency of nearly 100%. Although phosphorescent OLEDs (PhOLEDs) can potentially meet the requirements for practical display and lighting applications, however, phosphorescent complexes consisting of transition metals which could be possibly suffering from the rarity in natural resources, rendering the cost-down production of PhOLEDs relatively challenging. Recently, high efficiency OLEDs adopting pure organic emitter with thermally-activated delayed fluorescence (TADF) have been developed. Currently, some TADF emitters can deliver efficiencies largely exceed the previous efficiency limit of fluorescent OLEDs and are comparable to state-of-the-art PhOLEDs. TADF material needs to have a small energy gap (ΔES-T) between the first triplet excited state (T1) and the first singlet excited state (S1), allowing for efficient collection of electro-generated triplet excitons via reverse intersystem crossing (RISC). We collaborated with Prof. K.-T. Wong's group for developing a blue-emitting and a green-emitting TADF materials, which were respective named CzPTTPA-1 and CzPTTPA-3. Both TADF emitters were used to fabricate TADF OLEDs. The maximum efficiencies of OLEDs with CzPTTPA-1 and CzPTTPA-3 were achieving 13.2% (39.8 cd/A, and 29.8 lm/W) and 18.0% (45.5 cd/A and 35.7 lm/W), respectively. Furthermore, both TADF materials were used as sensitizers for enhancing the efficiency of fluorescent or phosphorescent OLEDs. The strong reverse intersystem crossing enables TADF sensitizer to harvest both singlet and triplet excitons. Then, the energy of TADF sensitizer could transfer to the fluorescent or phosphorescent emitters and then increases the efficiency of the TADF sensitized OLEDs. Comparing to the TBRb-based fluorescent OLEDs, 279% or 327% efficiency improvements could be obtained respectively in the sensitized TBRb-based fluorescent OLEDs by using CzPTTPA-1 or CzPTTPA-3 sensitizers. On the other hand, TADF sensitizers could be used to increase the efficiency of PhOLEDs with low doping concentration. Comparing to the Ir(ppy)3-based PhOLEDs, the efficiency enhancement of the sensitized OLEDs with CzPTTPA-1 or CzPTTPA-3 sensitizers were up to 118%. These results demonstrated that both CzPTTPA-1 and CzPTTPA-3 TADF materials possess high potential for the EL applications.