Efficiently red-emitting dimethoxybenzothiadiazoles for organic doping-free devices enabling stable warm-white electroluminescence.

The study provides guidance for developing doping-free white organic light-emitting diodes (OLEDs) with single or double light-emitting layers and offers insights into molecular structure-property relationships for highly efficient dimethoxybenzothiadiazole-based emitters. To achieve white electroluminescence, newly synthesised dimethoxybenzothiadiazole derivatives were used as red fluorescent emitters in combination with emitters exhibiting efficient thermally activated delayed fluorescence (TADF), such as a sky-blue exciplex emitter or a conventional green emitter. The developed compounds exhibit photoluminescence quantum efficiencies of up to 98% in solutions, hole mobilities exceeding 1 × 10-4 cm2 V-1 s-1 at electric fields above 1 × 106 V cm-1, ionisation energies of ca. 5.6 eV, and electron affinities of ca. 3.4 eV. These properties enabled us to fabricate doping-free OLEDs with an external quantum efficiency (EQE) of up to 3.34% and red electroluminescence with CIE1931 (x, y) colour coordinates (0.54, 0.36). The sky-blue exciplex-based TADF emitter tunes the colour coordinates and enhances EQE by up to 8.5%. The green TADF emitter enabled us to achieve stable warm-white electroluminescence in OLEDs with double, fully doping-free light-emitting layers, exhibiting EQE up to 8.23%, and colour coordinates of x up to 0.43, and y up to 0.38.