Narrowband Emissive Solution‐Processed Polymer Organic Light‐Emitting Diodes with External Quantum Efficiency Above 30%

Abstract Achieving both high‐efficiency and narrowband emission in thermally activated delayed fluorescence (TADF) polymers remains a formidable challenge. In this work, a proof of concept for narrowband‐emissive TADF polymers with a partially conjugated structure is proposed by embedding a silicon─carbon σ‐bond saturated spacer between the multiresonance (MR) TADF unit and the polycarbazole backbone. A series of TADF polymers PSix ( x = 1, 3, and 6) is then prepared and characterized. All the polymers show narrowband emission with full width at half maximum (FWHM) values of 28–30 nm in a toluene solution. Impressively, polymer PSi3 has the highest photoluminescence quantum yield, reaching 97%, in the doped films due to the efficient reverse intersystem crossing process. The solution‐processed devices based on PSi3 exhibit the best performance with a maximum external quantum efficiency ( EQE max ) of 28.8% and an FWHM of 42 nm. By employing the TADF molecule 5Cz‐TRZ as the sensitizer, enhanced device performance with an EQE max of 30.2% is achieved, which is in the first tier among the MR‐TADF polymers reported to date. This work provides an effective strategy for achieving highly efficient and narrowband‐emissive TADF polymers by controlling the σ‐bond saturated spacer between the MR‐TADF chromophore and the polymer backbone.