Highly Efficient Deep Blue Fluorescent Organic Light-Emitting Diodes Boosted by Thermally Activated Delayed Fluorescence Sensitization

Highly efficient deep blue fluorescent material and various thermally activated delayed fluorescent (TADF) blue sensitization materials were synthesized for fluorescent deep blue organic light-emitting diodes (OLEDs). These materials were designed and selected by considering efficient energy transfer conditions (i.e., spectral overlap and quantum efficiency) between sensitizer and acceptor. Energy transfer process from TADF host sensitizers to deep blue fluorescent emitter has been investigated by measuring the energy transfer rate. Measured energy transfer rate was to be 1.24 × 10<sup>10</sup> s<sup>–1</sup> (mol/dm<sup>3</sup>)<sup>−1</sup> for a prompt decay of fluorescence and 2.61 × 10<sup>8</sup> s<sup>–1</sup> (mol/dm<sup>3</sup>)<sup>−1</sup> for delayed fluorescence, which demonstrated the efficient energy transfer. Indeed, highly efficient deep blue fluorescent OLEDs boosted by the TADF host-sensitization process were successfully fabricated. The maximum external quantum efficiency was 19.0% with color coordinates of (0.14, 0.15) and 15.5% with color coordinates of (0.15, 0.11) in the different host system. The efficiency roll-off characteristic and device operating lifetime were also improved by this efficient sensitization process.