Unified Framework for Photophysical Rate Calculations in TADF Molecules

One of the challenges in organic light-emitting diodes research is finding ways to increase device efficiency by making use of the triplet excitons that are inevitably generated in the process of electroluminescence. One way to do so is by thermally activated delayed fluorescence (TADF), a process in which triplet excitons undergo upconversion to singlet states, allowing them to relax radiatively. The discovery of this phenomenon has ensued a quest for new materials that are able to effectively take advantage of this mechanism. From a theoretical standpoint, this requires the capacity to estimate the rates of the various processes involved in the photophysics of candidate molecules, such as intersystem crossing, reverse intersystem crossing, fluorescence, and phosphorescence. Here, we present a method that is able to, within a single framework, compute all of these rates and predict the photophysics of new molecules. We apply the method to two TADF molecules and show that results compare favorably with other theoretical approaches and experimental results. Finally, we use a kinetic model to show how the calculated rates act in concert to produce different photophysical behavior.

Automated summary

One of the challenges in organic light-emitting diodes research is increasing device efficiency by utilizing triplet excitons through thermally activated delayed fluorescence (TADF). The key is to find new materials that can effectively take advantage of this mechanism, which requires estimating rates of various photophysical processes involved in candidate molecules. This method can predict the photophysics of new molecules and compare favorably with other theoretical approaches and experimental results.