image: Schematic illustrations of Device strategy for sandwich structure B-R-B WOLED. WOLEDs are fabricated with robust MR-TADF emitters as blue emitters in EML-B, and PO-01 as yellow sensitizer for red emitter DB3 in EML-R. Efficient Förster energy transfer (FRET) among emitters results in high efficiencies and stable emission spectra.
Credit: by Guohao Chen, Jingsheng Miao et al.
White organic light-emitting diodes (WOLEDs) are considered an ideal solution for next-generation lighting due to their flexibility, energy efficiency, and eye-protection properties. However, the commercialization of WOLEDs has been hindered by challenges such as the instability of blue emitters and the inefficient use of triplet excitons, which are crucial for optimizing performance. To address these issues, a team of scientists led by Professor Chuluo Yang from the Shenzhen Key Laboratory of New Information Display and Storage Materials at Shenzhen University, China, introduced a novel approach in a recent paper published in Light Science & Applications. They integrated blue MR-TADF emitters with a rigid π-conjugated core skeleton as the blue component in the emitting layer (EML-B), and combined it with a red MR-TADF emitter (DB3) and a yellow phosphorescent sensitizer, iridium (III) bis(4-phenylthieno[3,2-c]pyridinato-N,C2')acetylacetonate (PO-01), as the red component in the emitting layer (EML-R), thereby constructing a high-efficiency white-light system.
By carefully selecting MR-TADF emitters and optimizing the exciton recombination zone, the researchers significantly enhanced device performance. The optimized tri-color hybrid devices based on BCzBN-3B demonstrated stable white light emission, achieving a maximum external quantum efficiency (EQEmax) of 34.4% and a power efficiency (PEmax) of 101.8 lm/W, marking a breakthrough in WOLED technology. Additionally, a hybrid WOLED incorporating the deep blue emitter BN3 achieved a high color rendering index (CRI) of 88 and an EQEmax of 30.6%, further highlighting the versatility and effectiveness of their approach. Moreover, the researchers achieved remarkable stability, with a luminance lifetime LT90 (the time for the luminance to drop to 90% of its initial value) of 761 hours at 1000 cd/m² for the BCzBN-3B-based device, demonstrating its potential for long-lasting applications.
The breakthrough of hybrid WOLEDs based on MR-TADF emitters paves the way for the mass commercialization of WOLEDs. Looking ahead, the integration of blue MR-TADF materials with enhanced reverse intersystem crossing rates, combined with further optimization of device structures, is expected to lead to WOLEDs with improved performance and lower production costs. This progress will open up new possibilities for energy-efficient and high-performance lighting and display solutions.
Journal
Light Science & Applications
Article Title
High-power-efficiency and ultra-long-lifetime white OLEDs empowered by robust blue multi-resonance TADF emitters