Recently, phosphorescent organic light-emitting diodes (OLEDs) have received a great attention because they can harvest singlet and triplet exciton. In the case of blue phosphorescent OLEDs, their efficiency is still lower than red and green OLEDs. One of the biggest problems of their low efficiency is the leakage of hole and triplet exciton in the emitting layer (EML). If the highest occupied molecular orbital (HOMO) energy level of the electron-transporting layer (ETL) adjacent to the EML is higher than that of emitting materials, the hole can be migrated into ETL. In addition, if the triplet energy is lower than that of emitting materials, the ETL can quench the triplet energy. In order to confine the hole and triplet exciton in the EML, hole-blocking materials (HBMs) having a high triplet energy and deep HOMO energy level must be introduced between the EML and ETL. Furthermore, it is well known that low glass transition temperature (Tg) characteristics of OLED materials tend to shorten the device lifetime due to thin film crystallization during OLED driving. Therefore, new HBMs with high Tg as well as high triplet energy and deep HOMO energy level must be developed. In this work, we designed and synthesized two HBMs, mPyrPPB and pPPyrPB, using pyrimidine and phenylene segments. The thermal and optical, and electrochemical properties of two materials were systematically investigated by using thermogravimetric analysis, differential scanning calorimetry, UV-visible and photoluminance spectrometry, and cyclic voltammetry. Furthermore, the relationship between the structure of organic molecular and their corresponding effect was studied by quantum chemical computation. In the case of mPyrPPB, it is found that it has high triplet energy, Tg, and deep HOMO energy level as 2.77 eV, 118 oC, and 6.86 eV, respectively, to achieve high-performance OLEDs. As a result of applying mPyrPPB to blue phosphorescent OLEDs, external quantum efficiency (EQE), current efficiency (CE), power efficiency (PE) increased by 38%, 35%, and 54%, respectively. Their structure-property relationship of new hole-blocking materials for highly efficient blue phosphorescent OLEDs will be presented.

Design and synthesis of high-performance hole blocking materials with high triplet energy and glass transition temperature for blue phosphorescent organic light-emitting diodes

256th National Meeting (2018)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.