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

Abstract 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.