Highly efficient yellow nondoped thermally activated delayed fluorescence OLEDs by utilizing energy transfer between dual conformations based on phenothiazine derivatives

Abstract

The nondoped thermally activated delayed fluorescence (TADF) devices are increasingly attracting attention due to the superior performances and simple fabrication process. By incorporating two acceptors with phenothiazine, two materials 2-(10H-phenothiazine-10-yl)-10-phenyl-10H-phenothiazine-5,5-dioxide (PTZ-2PTO) and 3-(10H-phenothiazin-10-yl)-10-phenylacridin-9(10H)-one (PTZ-AD) are designed and investigated. Both the two materials possess dual conformations, whereas the quasi-axial conformer is the main configuration of PTZ-2PTO and quasi-equatorial conformer of PTZ-AD is more stable. The quasi-axial conformers show classical fluorescence emission, and the quasi-equatorial conformers exhibit TADF characteristic. Fascinatingly more, efficient energy transfer can be achieved between quasi-axial conformers and quasi-equatorial conformers, exhibiting similar mechanism to the traditional host-guest system. Based on this characteristic, yellow nondoped TADF-OLED device of PTZ-AD has realized the efficiency of up to 17.08%, 50.48 cd A−1 and 60.04 lm W−1. Meanwhile, the PTZ-AD based nondoped device exhibits low turn-on voltage and low efficiency roll-off, which is among the best performance for yellow nondoped TADF devices. In addition, PTZ-AD based doped device realizes high efficiency of 20.23%, 61.04 cd A−1 and 68.45 lm W−1. This dual conformations forming host-guest system provides a new strategy for obtaining highly efficient nondoped OLEDs devices.