Recent endeavors and perspectives in developing solution-processable host materials for thermally activated delayed fluorescence organic light-emitting diodes

Solution-processable thermally activated delayed fluorescence (TADF) organic light-emitting diodes (OLEDs) have attracted increasing attention in academia and industry owing to their feasibility for fabricating large-area and flexible devices. Solution-processable devices have numerous advantages, including low cost and easy fabrication without the need for harsh conditions such as high temperature, as well as reduced material waste. Highly efficient OLEDs are conventionally fabricated by blending emissive materials into a host matrix to alleviate concentration quenching, triplet-triplet annihilation, and unwanted red-shifted emission. However, the host materials have been relatively less explored than TADF emissive materials owing to difficulties in the design and synthesis of the former materials. Therefore, there is an urgent need for a comprehensive review manifesting design, synthesis, and techniques of fabricating solution-processable host materials for TADF emitters of different colors. This review clearly describes the design tactics and structure-property relationships of solution-processable host materials for TADF OLEDs. The chemical structures of the previously reported host materials are clearly outlined, and their photophysical and electroluminescence properties are summarized. Finally, insights and prospects are provided to further promote the proposed research field. This review is expected to attract considerable attention from the OLED community and promote the development of solution-processable and flexible TADF OLEDs for future display and lighting technologies. Indeed, the development of solution-processable host materials for TADF OLEDs is less explored. This review aims to provide a comprehensive overview of the progress made in the exploration of host materials for solution-processable TADF OLEDs.