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

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.