Progress on Donor-Acceptor Type Thermally Activated Delayed Fluorescence Based Blue Emitters

In thermally activated delayed fluorescence (TADF) based emitters, the excitons from the lowest triplet state (T1) can be efficiently upconverted into the lowest singlet (S-1) state via reverse intersystem crossing (RISC) process due to the small energy gap (Delta E-ST) between their S1 and T1 states, harvesting both S1 and T1 excitons for emission, with non-noble metals, which can break the internal/external quantum efficiency (IQE/EQE) (<= 25%/<= 5%) limitation of conventional fluorescence based organic light-emitting diodes (OLEDs). Their no-noble metals feature makes them more competitive than phosphorescence materials in making OLEDs. Among the vast of TADF materials, eletrons donor-acceptor (D-A) type is one of the most popular TADF material due to their outstanding performance and convenience of preparation. On the other hand, efficient blue emitters are facing issues related to their stability and color purity that makes their development quite challenging for researchers. In this review, the D-A type blue TADF emitters and OLEDs reported recently are summarized, the mechanism of TADF based OLEDs and the principle of designs are elaborated, and a full vision of its development is made.