Kinetic Criteria for Optimal Thermally Activated Delayed Fluorescence in Photoluminescence and in Electroluminescence

A complete set of criteria for the classification, design, and selection of optimal thermally activated delayed fluorescence (TADF) emitters, for both photoluminescence and electroluminescence applications, is presently unavailable. In this work, and as a contribution toward this aim, a detailed characterization of TADF photophysical kinetics is presented, contrasting TADF in photoluminescence and TADF in electroluminescence. Two different types of TADF are identified: One-way and two-way TADF. It is shown that, for a given efficiency, one-way TADF allows lower rates of reverse intersystem crossing, an aspect that may be significant with respect to stability and roll-off issues. Graphical and quantitative indicators of singlet–triplet interconversion and photophysical efficiency are obtained and applied to the photoluminescence of eosin, coronene, and fullerenes and to the electroluminescence of several TADF emitters specifically designed for organic light emitting diodes. Relations for the photoluminesce...