Ultrapure deep-blue aggregation-induced emission and thermally activated delayed fluorescence emitters for efficient OLEDs with CIEy < 0.1 and low efficiency roll-offs

Abstract

The development of pure deep-blue emitters with excellent optoelectronic and electroluminescence (EL) properties is full of challenges due to limited molecular designs. Herein, three novel color-tunable phenylcarbazole derivative based emitters from deep-blue to blue pCz-DPS, pCz-BTO and pCz-BP were demonstrated, which were designed by incorporating different short conjugation length building blocks as electron-accepting moieties and twisted rigid electron-donating carbazole derivatives. These emitters show deep-blue to blue emission, thanks to the deep highest occupied molecular energy level of the carbazole derivative donor units. In addition, pCz-BP exhibits aggregation-induced emission (AIE) properties, while pCz-BTO exhibits AIE and thermally activated delayed fluorescence (TADF) properties simultaneously. Nondoped organic light-emitting diodes (OLEDs) using these emitters as emission layers were fabricated, along with a maximum external quantum efficiency (EQE) and Commission Internationale de l’Éclairage (CIE) color coordinates of 7.1% and (0.15, 0.10) for pCz-BTO devices. The pCz-BTO emitter can also function robustly in doped OLEDs with an impressive maximum current efficiency (CE) and EQE of 23.3 cd A⁻¹ and 9.5%, respectively, along with ultrapure blue color CIE coordinates of (0.15, 0.09). The significantly excellent performance of pCz-BTO could be ascribed to excellent photoluminescence quantum yield (PLQY), high reverse intersystem crossing rate constant (k_RISC) and high fluorescence decay rate constant (k_F) values. The excellent performance, ultrahigh color purity and extremely low efficiency roll-off of pCz-BTO are among the state-of-the-art deep-blue emitters, indicating the great potential of these materials in the application of ultrapure deep-blue OLEDs.