Single White‐Emitting Polymers with High Efficiency, Low Roll‐Off, and Enhanced Device Stability by Using Through‐Space Charge Transfer Polymer with Blue Delayed Fluorescence as Host for Yellow Phosphor

Abstract White‐emitting polymers hold great promise for the production of low‐cost and large‐area light sources via solution process. However, the development of efficient and stable white‐emitting polymers has been a formidable challenge yet. Here a strategy for single white‐emitting polymers is demonstrated with high efficiency, low roll‐off, and enhanced device stability by using through‐space charge transfer (TSCT) polymer with small singlet‐triplet energy splitting and blue thermally activated delayed fluorescence as host for yellow phosphor. This strategy not only combines delayed fluorescence and phosphorescence in one polymer to make full use of excitons but also enables the long‐range Förster resonant energy transfer from polymer host to phosphor for suppressing triplet quenching at high luminance, leading to state‐of‐the‐art luminous efficiency of 50.9 cd A⁻¹ at 1000 cd m⁻² (corresponding to a low roll‐off of 1.9%) for white‐emitting polymers, together with a tenfold increase in device lifetime over the control polymers based on a conventional polymer host. These results shed light on the prospect of using TSCT polymer with delayed fluorescence as host for developing efficient and stable white‐emitting polymers for solution‐processed white organic light‐emitting diodes.