Carbazole and carbazole-related compounds have been studied for their unique electrical, electrochemical and optical-physical properties in the past decades. This kind materials are typical hole transporting unit due to the electron donating character and can be easily modified with electron transport units in different position. Thereby, the injection of electrons and holes simultaneously into deep blue emitters becomes more facility, meanwhile, there is a good balance between electrons and holes. It is believed that carbazole and carbazole-related compounds have great promise as photoelectric functional materials for their photo-physical and fluorescent properties in the blue light region. Carbazole and carbazole-related compounds not only can be used as small molecular in fluorescence materials, phosphorescence materials and thermally activated delayed fluorescence materials, but also as high molecular. Recently, the syntheses of carbazole and carbazole-related materials and their applications have become the highlight in blue emitting organic light-emitting diodes. In this review, we summarize recent progress of small molecular carbazole and carbazole-related materials as organic light emitting materials. The molecular design concept, the electric structure, optical physical properties, thermal stability, electrochemical properties and the properties of carbazole-based OLEDs are reviewed as well.Meanwhile, carbazole-containing polymers OLED materials also be discussed. At last, the perspectives of foreseeable future and trend of development of carbazole-based OLEDs are also presented. Considering the conversion efficiency of electrical-to-optical and the cost of OLED, thermally activated delayed fluorescence (TADF) and polymer light-emitting materials (containing carbazole-based groups) are most attractive tendency to blue OLEDs.

Contents
1 Introduction
2 Small organic molecular carbazole-based blue emitting materials
2.1 Carbazole-based fluorescence materials
2.2 Carbazole-based phosphorescence materials
3 Carbazole-based thermally activated delayed fluorescence materials
4 Carbazole-containing polymers blue emitting materials
4.1 Polymers with pendant carbazolyl moieties
4.2 Polymers containing carbazole moieties in the main chain
5 Conclusion and outlook