Dual-acceptor thermally activated delayed fluorescence emitters: Achieving high efficiency and long lifetime in orange-red OLEDs

The efficiency and lifetime are critical to the development of high-quality organic light-emitting diodes (OLEDs). Herein, four dual-acceptor typed thermally activated delayed fluorescence (TADF) emitters (DTXO-PhCz2, DTXO-PhCz4, DTXO-TPA2 and DTXO-TPA4) with emission from yellow to red were designed by taking triphenylamine or N-phenylcarbazole as the donor and 9-H-thioxanthen-9-one-10,10-dioxide (TXO) as the acceptor. All of the devices based on these emitters showed outstanding performance. Particularly, depending on superior electronic properties, DTXO-TPA2 showed the maximum photoluminescence quantum yield (PLQY) and horizontally oriented emitting dipole. As a result, the orange-red OLED based on DTXO-TPA2 achieve maximum external quantum efficiency (EQE) of 24.98% and power efficiency (PE) of 77.74 lm W−1. And, thanks to the stable molecular framework and favorable device characteristics, the lifetime value of DTXO-TPA2-based device can reach up to 1392 h at 50% of the initial luminescence of 1000 cd m−2. Furthermore, the white OLED based on DTXO-TPA2 can achieve high EQE of 17.96% and color rendering index of 85 with CIE of (0.31,0.31). This work supports an effective design strategy about increasing TXO acceptor moieties for the orange-red TADF materials to develop highly efficient and long-lived OLEDs.