Recent advances in regulating the excited states of conjugated thermally activated delayed fluorescence polymers for high-efficiency OLEDs

A detailed overview of thermally activated delayed fluorescence conjugated polymers reported from 2015 to present is provided, with a focus on their molecular structures, excited-state properties, and organic light-emitting diode performance. In addition, the rules for regulating the excited-state properties of these TADF conjugated polymers are summarized. By carefully designing the molecular structures of conjugated TADF polymers, their excited-state properties and the energy gaps between the lowest singlet excited states and the lowest triplet excited state can effectively be adjusted. Furthermore, the reverse intersystem crossing rate of conjugated polymers can be increased by enhancing the spin-orbit coupling effect between the triplet and singlet states, and thus optimizing the collection of triplet excitons and improving the device performance, including external quantum efficiency and efficiency roll-off. Several methods are summarized for controlling the excited states of TADF conjugated polymers, covering: (a) maintaining suitable Delta EST; (b) localized triplet excited state assisted reverse intersystem crossing; (c) hyperfine coupling facilitates reverse intersystem crossing.