Reliable prediction of the singlet-triplet gap in TADF molecules with GW/BSE approach

Organic light emitting diode (OLED) molecules that exhibit thermally activated delayed fluorescence (TADF) have emerged as a promising technology for various lighting and display applications. Such systems depend on low singlet-triplet gaps of the order of kT to allow reverse inter-system crossing. Here, we demonstrate the capability of a GW/BSE method to predict excitation energies and singlet-triplet gaps. We compare the results with time-dependent density functional theory of two organic molecules. The BSE results (in comparison to TDDF-TTDA) show absolute minimum deviations of 0.04 eV in the first absorption peak and 0.04 eV in the singlet-triplet splitting for the PhCz molecule and serve as a reliable tool to explore the design concepts in TADF molecules with small singlet-triplet splittings.