Highly Efficient and Bright Blue OLEDs via TSCT-TADF Molecule Regulated by Indolo[3,2,1-jk]Carbazole

Abstract

Thermally activated delayed fluorescence (TADF) materials with the through-space charge transfer (TSCT) effects can provide a useful approach to efficiently utilize dark state triplet excitons through an efficient reverse intersystem crossing process. TSCT-TADF emitters PCzoTrz-ICz with small ∆E_ST values and high photoluminescence quantum yield is designed and synthesized using common acceptor triazine, donor 3,6-diphenylcarbazole and Indolo[3,2,1-jk]carbazole which is a rigid π-conjugated group with high triplet state and high thermal stability. The doped-organic light-emitting diodes using PCzoTrz-ICz as emitters exhibit high tolerance to host with different polarity and charge transport properties, and PCzoTrz-ICz doped devices in 2,8-bis(diphenylphosphoryl)dibenzofuran even realizes a maximum external quantum efficiency (EQE_max) of 32.5% and maximum current efficiency (CE_max) of 74.1 cd A⁻¹, which is higher than EQE_max of 28.1% and CE_max of 64.8 cd A⁻¹ of PCzoTrz. Moreover, PCzoTrz-ICz can be used as highly efficient sensitizers for narrow band blue emitter of v-DABNA, and achieves more than EQE_max of 33.3%, maximum luminance of 26,291 cd m⁻², CE_max of 42.7 cd A⁻¹ and blue index of 237 cd A⁻¹ CIE_y⁻¹.