High-permanent dipole moment sensitizers as key to anticharge trapping of terminal dopant in highly efficient phosphor-sensitized fluorescence systems

To design a highly efficient phosphor-sensitized fluorescence (PSF) system, it is crucial to suppress hole trap formation in the terminal dopant. However, strategies to suppress hole trap formation in terminal dopants have not been fully explored. In this study, we propose an approach to improve the overall performance of PSF devices by addressing charge trapping in the terminal dopant using high-permanent dipole moment (PDM) phosphorescent sensitizers. Through the cascade modulation of high PDM and trap energy, the trapped charges in the terminal dopant were significantly suppressed. The phosphorescent sensitizer with high PDM and shallow highest occupied molecular orbital (HOMO) energy levels exhibited the highest trap suppression capability. The enhanced trap suppression capability resulted in a 391% improvement in the external quantum efficiency and a threefold increase in the device lifetime compared to a TBRB-only device. Finally, we present a guideline for selecting phosphorescent sensitizers with high trap suppression capability based on the combined influence of PDM and trap energy levels via impedance spectroscopy. This framework provides valuable insights into the development of advanced PSF systems.