A research team led by Prof. CUI Songlin at University of Science and Technology of China (USTC), in collaboration with Prof. ZHOU Meng's team from Beijing Information Science and Technology University (BISTU) has proposed a new strategy for designing pure-red organic light emitting diodes (OLED) materials. These materials have achieved a milestone with electroluminescence efficiencies exceeding 43%, marking a significant step towards high-performance ultrahigh-definition OLED displays. The study was published online in the Journal of the American Chemical Society.

OLEDs have emerged as a leading technology due to their unique features such as flexibility and bright self-emission. However, the performance of red OLEDs, especially in the saturated red region, has lagged behind that of blue and green counterparts. The development of efficient red emitters with high color purity has been a major challenge in the field.

Focusing on overcoming the challenge of red light emitters, the research team proposed a new strategy for the design of pure-red OLED materials with high luminous efficiency, excellent color purity, and long-term stability. The key innovation lies in the molecule BNTPA, which was designed to incorporate secondary electron-donating units and extend the π-skeleton within multiresonance cores. This structural modification significantly enhances intramolecular charge transfer, enabling the molecule to more efficiently handle the excitation energy.

As a result, light emission is effectively shifted into the red spectrum, while still maintaining narrowband characteristics for ensuring high color fidelity, which is a key requirement for high-definition displays. To further improve the molecular design, the team optimized the reverse inter-system crossing (RISC) process. BNTPA’s refined structure not only accelerates the RISC rate but also ensures a balanced combination of short-range and long-range charge transfer characteristics.

This balance is particularly important for improving the overall photophysical performance of the emitter, as it minimizes energy loss and improves both the luminous efficiency and stability of the OLEDs. Additionally, the integration of secondary electron-donating units stabilizes the excited states of BNTPA, reducing non-radiative decay and preventing energy loss that often occurs in red-emitting materials. This enhancement of the molecular architecture ensures that BNTPA-based OLEDs achieve greater operational stability and longer lifetimes, making them suitable for practical, long-term use in real-world applications.

Molecular design concept and chemical structures of the emitters. (Image from USTC)

Finally, OLEDs based on BNTPA achieved a record-breaking external quantum efficiency exceeding 43%. Its CIE value is (0.657, 0.343), aligns closely with NTSC standards (0.67，0.33), achieving excellent color purity. These advancements are attributed to the molecule's optimized design, which enhances energy efficiency and operational stability. This establishes BNTPA as a benchmark for next-generation high-performance red MR-TADF emitters.

This research sets a precedent for future research and practical deployment in high-definition displays and next-generation electronic devices. It also contributes to the development of energy-efficient and durable lighting systems, enabling OLED displays to meet stringent color standards.

Paper link: https://pubs.acs.org/doi/10.1021/jacs.4c13375

(Written by ZHENG Zihong, Edited by WU Yuyang, USTC News Center)