Recent advances in green thermally activated delayed fluorescence emitters towards high colour purity and good electroluminescence performance

The conventional donor-acceptor (D-A) and donor-acceptor-donor (D-A-D) types of thermally activated delayed fluorescence (TADF) emitters manifested excellent electroluminescence efficiencies in recent years. However, the color purity of these emitters is not satisfactory due to the enhanced charge transfer characteristics. Such broad emission spectra with wide full width at half maximum (FWHM) must be narrowed down for their potential implementation in ultrahigh-definition display technology. Recently, polycyclic aromatic molecular skeleton-based emitters, specified as multi resonance (MR) type of TADF emitters, have drawn immense attention due to the achievable high color purity required by the standard. However, making bathochromic shifted and controlled emission (green) using a polycyclic aromatic core is identified as one of the challenging parts of molecular designing. Several strategies are implemented towards the development of green emitters without affecting the electroluminescence efficiencies. This review focuses on the recent progress of green emitters from the perspective of molecular design strategy and electroluminescence performance, offering a brief overview of highly efficient conventional green TADF emitters and MR-TADF emitters. Conventional green TADF emitters are selected to discuss their device performance corresponding with the molecular design evolution. At the same time, MR-TADF types of green emitters are comprehensively discussed due to their inherent need in future display technology.