Recently all-organic thermally activated delayed fluorescent (TADF) emitters have attracted great attention. In TADF emitters, nonemissive triplet states can be also harvested via population of emissive singlet states through reverse intersystem crossing (RISC). The RISC can be induced by the small energy gap between the lowest singlet (S1) and triplet (T1) states. Due to this ability of TADF, 100% internal quantum efficiency and high maximum external quantum efficiency (EQEmax) comparable to those of phosphorescent organic light emitting diodes (OLEDs) have been already reported in TADF OLEDs. In this study, we demonstrate high efficiency TADF OLEDs which are attributed to employing triazine acceptor type TADF compounds having high RISC rates(kRISC).