A solution-processable host material of 1,3-bis{3-[3-(9-carbazolyl)phenyl]-9-carbazolyl}benzene and its application in organic light-emitting diodes employing thermally activated delayed fluorescence

Abstract

Solution-processed organic light-emitting diodes (OLEDs) that employed an efficient green thermally activated delayed fluorescent dopant of (4s,6s)-2,4,5,6-tetra(9H-carbazol-9-yl)isophthalonitrile (4CzIPN) and small molecular hosts were thoroughly investigated. We demonstrated that increasing the electron injection and transport capabilities of the electron transport layers as well as the glass transition temperature (T_g) of the host material can significantly improve the half-life of the OLEDs. Using a novel host material of 1,3-bis{3-[3-(9-carbazolyl)phenyl]-9-carbazolyl}benzene (CPCB) with a high triplet energy level of 2.79 eV and a high T_g of 165 °C, a solution-processed 4CzIPN-based OLED achieved an external electroluminescence quantum efficiency of 10% and a half-life of nearly 200 hours with an initial luminescence of 1000 cd m⁻². This was comparable to a device that used a dry-processed emissive layer.