The search for eicient materials for organic light emiting diodes is one of the most imperative research area. The focus is to obtain a bright large area emiter, limited by the low internal quantum eiciency of conventional organic emiters. Recently, a new generation of the organic materials (TADF) with a theoretical internal quantum eiciency up to 100%, opened new frameworks. However, signiicant challenges persist to achieve full understanding of the TADF mechanism and to improve the OLEDs stability. Starting from the photo-physical analysis, we show the relationship with the molecular electrical carrier dynamics and internal quantum eiciencies. The OLED structure, fabrication, and characterization are also discussed. Several examples for the full color emiters are given. Special emphasis on experimental results is made, showing the major milestones already achieved in this field.