π-Extended Carbazole Derivatives as Host Materials for Highly Efficient and Long-Life Green Phosphorescent Organic Light-Emitting Diodes

High-performance organic light-emitting diodes (OLEDs) that use phosphorescent and/or thermally activated delayed fluorescence emitters are capable of realizing 100 % electron-to-photon conversion. The host materials in these OLEDs play crucial roles in determining OLED performance. Carbazole derivatives are frequently used as host materials, among which 3,3-bis(9H-carbazol-9-yl)biphenyl (mCBP) is often used for lifetime testing in scientific studies. In this study, the pi conjugation of the carbazole unit was expanded to enhance OLED lifetime by designing and developing two benzothienocarbazole (BTCz)-based host materials, namely m1BTCBP and m4BTCBP. Among these host materials, m1BTCBP formed a highly efficient [Ir(ppy)(3)]-based OLED with an operational luminescence half-life (LT50) of over 300 h at an initial luminance of approximately 12000 cd m(-2) (current density: 25 mA cm(-2)). The LT50 value at 1000 cd cm(-2) was estimated to be about 23 000 h. This performance is clearly higher than that of mCBP-based OLEDs (LT50 approximate to 8500 h).

Automated summary

In this study, by designing and developing benzothienocarbazole-based host materials, the pi conjugation of the carbazole unit was expanded to enhance OLED lifetime. The new material m1BTCBP demonstrated higher performance compared to mCBP, with an operational luminescence half-life of 300 hours.