Constructing Cation‐π Interactions within Thermally Activated Delayed Fluorescence Polysiloxanes for High‐Efficiency Non‐Doped and Flexible OLEDs

High-efficiency thermally activated delayed fluorescence (TADF) polymer is one of the excellent choices for solution-processable electroluminescent devices due to their 100% theoretical exciton utilization. Herein, different from the previous TADF copolymers with carbon-carbon main-chains, TADF polymers with silicon-oxygen main-chains are innovatively prepared by easily combing polysiloxanes with TADF and host units. The flexible polysiloxane chains are rigidified by the cation-π interaction between the electropositive silicon atoms and TADF units, resulting in reduced vibrational relaxation and thus the narrow full width at half maximum and high photoluminescence quantum efficiency. Consequently, solution-processed non-doped OLEDs based on the prepared homopolysiloxane PSiBPA reach a maximum external quantum efficiency (EQE) of 27% and EQE of 20% at 500 cd m^-2, which keeps at the forefront of non-doped polymer devices to date. Noteworthily, PSiBPA is the only high-efficiency homopolymer reported so far. Furthermore, PSiBPA presents outstanding mechanical properties.Thus, bendable OLEDs that demonstrate the maximum brightness and EQE barely starting attenuation with a bending radius of 2 mm are showcased. Moreover, the maximum brightness and EQE can still maintain 60% after 50 bends. The design strategy develops a novel approach to optimizing the properties of TADF polymers via cation-π interactions for constructing high-efficiency non-doped and flexible OLEDs.