The Research Of Highly Efficient Organic Light-emitting Devices Based On Thermally Activated Delayed Fluorescence

Organic light-emitting diodes(OLEDs) are attracting more and more attention for using in high quality flat panel displays and lighting applications, because OLEDs have many promising characteristics such as high electroluminescence(EL) efficiency, extremely thin, printable, wider viewing angle, wide operating temperature, color temperature tenability, lower power consumption, light weight, transparent, and flexibility. Especially, OLEDs will be superior in 3D displays as their response is about 1000 times faster than that of LCD. At the same time, OLED is also a promising technology for future lighting. However, the efficiency and lifetime of OLED are still the key factors restricting its development. Nowadays, the third generation organic electroluminescent material with thermally activated delayed fluorescence(TADF) has achieved more and more increasing attention, because the internal quantum efficiency of TADF can be reached to 100% and the TADF is environment friendly without heavy metal element. It provides a new opportunity for the development of OLED.In this thesis, we have designed and fabricated high efficiency OLEDs based on TADF materials synthesized by our group.This thesis mainly includes two parts: firstly, the green TADF of TXO-Phcz as guest. The device showed the maximum EQE and the current efficiency of 20% and 58 cd A-1, respectively. It was twice superior to the same structure device based on Ir(ppy)3.What’s more, we have aslo tried to encapsulate these devices. Because of our packaging technology is not mature,the LT50 of TADF-OLED was only 80 h which was equal to the LT50 of Ir(ppy)3 based-OLED of 75 h. It suggested our TADF was the high performance luminescent materials which can be compared to Ir(ppy)3. Secondly, we have designed and fabricated the inverted bottom-emission TADF organic light emitting diodes. The Zn O and Cs2CO3 were utilized as the electron injection layer(EIL) and electron-injection interlayer(IL), respectively. The ZnO and Cs2CO3 can reduce electronic injection barrier to ensure the efficient injection and improve the performance of the inverted OLED. Finally,the maximum EQE and current efficiency were 10% and 28 cd A-1 based on TXO-Phcz inverted OLED. What’s more, the minimum turn-on voltage was around 4V, which was similar to the conventional devices.