Purely organic TADF emitters have been rapidly developed in recent years and their TADF has become one of the most promising achievement towards highly efficient OLEDs. Apart from the advantages such as stable structure, low-cost and high internal quantum efficiency of these emitters that have been found, the demand for high colour purity has become a new challenge. There have been many reports that show possibilities of designing narrowband TADF emitters using totally different methods. Recently, TADF emitters have exhibited a narrow emission with a FWHM of below 20 nm. Therefore, broad emission spectra and bad colour purity shall not always be considered as fatal defects of TADF emitters. Herein, a review of narrowband TADF emitters is presented with a focus on the molecular design, photophysical properties and performance of the corresponding OLED devices. Besides, this review will exhibit the common characteristics of emitters for the purpose of further designs.