AbstractThermally activated delayed fuorescent (TADF) polymers are very suitable for fabricating highly efficient solution‐processed organic light emitting diodes (OLEDs). TADF homopolymers with simple structures are much preferred for preparation, but due to the triplet–triplet annnihilation, most TADF homopolymeric OLED exhibits lower external quantum efficiency (EQE) than its TADF repeating unit. Herein, two series small molecules (CzPhO and PxPhO) and their related mono‐polymers (PCzPhO and PPxPhO) are designed and synthesized for comparison. Among them, phenoxazine‐based materials show TADF properties compared to the carbazole‐based materials, which may be due to the enhanced electron donating ability of phenoxazine unit. In addition, the solution‐processed devices based on phenoxazine‐based polymer PPxPhO give excellent performance compared to their counterparts with the EQEmax of 11.8%.