A facile method to achieve red thermally activated delayed fluorescence emitters with EQE over 30% via molecular aspect ratio engineering

作者：Liang, Jing-Xing; Pan, Ze-Hui; Zhang, Kai; Yang, Dezhi; Tai, Jing-Wen; Wang, Chuan-Kui^*; Fung, Man-Keung^*; Ma, Dongge^*; Fan, Jian^*

来源：Chemical Engineering Journal, 2023, 457: 141074.

DOI：10.1016/j.cej.2022.141074

• Organic light -emitting diodes
• Thermally activated delayed fluorescence
• Red electroluminescence
• Molecular aspect ratio
• Horizontal emitting dipole ratio

Bandgap narrowing via the incorporation of strong donor and/or acceptor units into the molecular structure is a well-known strategy for the design of the long-wavelength fluorophores. Due to the energy-gap law, achieving high emission quantum yield at long wavelength becomes a paradox. Therefore, the red fluorescence emitters with external quantum efficiency (EQE) over 30 % have rarely been reported in comparison with blue and green fluorophores. In this work, a series of the thermally activated delayed fluorescence (TADF) materials (PH-TPA, BZ-TPA and PO-TPA) featured with rigid skeleton demonstrated low non-radiative decay rates and high photoluminescent quantum efficiency. Importantly, the engineering of molecular aspect ratio of the TADF emitters led to high horizontal emitting dipole ratio, thus enhancing the device performance. As a result, organic lightemitting diodes based on PH-TPA, BZ-TPA and PO-TPA showed record-high EQEs of 33.0 % at 624 nm, 31.3 % at 634 nm and 34.9 % at 632 nm, respectively. This work provided a facile and yet effective method for the construction of efficient red TADFs via the integration of rigid emission core and the control of molecular aspect ratio.

• 单位
  苏州大学; 中国科学院福建物质结构研究所