3,9'-Bicarbazole is an organic compound consisting of two carbazole units linked at the 3- and 9-positions. It serves as a crucial building block in the field of organic electronics and advanced materials. Its primary application is as a high-performance hole-transporting material (HTM) and host material in organic light-emitting diodes (OLEDs). The rigid, planar, and conjugated structure of the bicarbazole core provides excellent thermal stability, high triplet energy, and good hole-transporting properties, making it ideal for use in phosphorescent OLED (PhOLED) devices. It is also widely used as a monomer or core unit for synthesizing various functional polymers and small molecules, such as polycarbazoles and star-shaped molecules, for applications in organic photovoltaics (OPV) and perovskite solar cells. Due to its versatile functionality, it is a key intermediate in the development of next-generation display and lighting technologies, as well as in the synthesis of electroactive polymers for electronic devices.