Reverse Intersystem Crossing Boosting Sensitizer for Ultra-High Efficiency Blue Organic Light-Emitting Diode

In designing thermally activated delayed fluorescence (TADF) emitters, a high reverse intersystem crossing (RISC) rate with a high photoluminescence quantum yield is essential. Herein, two blue TADF molecules, 2 ',5 '-di(9H-carbazol-9-yl)-3 ',6 '-bis(3,6-ditert-butyl-9H-carbazol-9-yl)-[1,1 ':4 ',1 ''-terphenyl]-4,4 ''-dicarbonitrile (CzTCzPhBN) and 2 ',5 '-bis(3,6-ditert-butyl-9H-carbazol-9-yl)-3 ',6 '-bis(3,6-diphenyl-9H-carbazol-9-yl)-[1,1 ':4 ',1 ''-terphenyl]-4,4 ''-dicarbonitrile (PhCzTCzPhBN) with a high RISC rate, were developed through donor engineering. CzTCzPhBN and PhCzTCzPhBN showed a high RISC rate of 4.00 x 10(5) and 16.62 x 10(5) s(-1), respectively, with a high photoluminescence quantum yield of 80.1 and 84.9%, which resulted in high external quantum efficiency of 27.0 and 27.8% with color coordinates (0.148, 0.170) and (0.150, 0.230) in blue TADF organic light-emitting diodes, respectively. The high RISC rate and device efficiency inspired two TADF molecules to be used as sensitizers in hyperfluorescence devices. The hyperfluorescence devices showed ultra-high external quantum efficiency of 30.7 and 36.4% with color coordinates (0.125, 0.164) and (0.127, 0.193), respectively.