High‐Efficiency TADF Polymers with a Spatially Confined Conjugated Backbone Enable Solution‐Processable Blue OLEDs Realizing over 20% EQE

Abstract The concept of thermally activated delayed fluorescence (TADF) conjugated polymers has the advantage of enabling solution‐processable devices and harnessing singlet and triplet excitons simultaneously, whereas the resultant redshift of emission spectra and inevitable drop‐off of triplet excited states are detrimental to exploring high‐efficiency blue conjugated polymeric emitters. Herein, a feasible molecular design strategy is proposed by combining a spatially confined conjugated backbone and a TADF moiety isolated by a saturated spiro spacer to enable blue emission in newly designed partly conjugated TADF polymers, simultaneously achieving an excellent photoluminescence quantum yield of over 80% and a relatively high reverse intersystem crossing rate of 4.2 × 10 5 s −1 . Endowed by superior photophysical properties and balanced carrier mobility, a maximum external quantum efficiency of 20.5% is achieved with emission at 486 nm and Commission Internationalede l'Eclairage coordinates of (0.18, 0.31), which is so far the highest efficiency for solution‐processed blue TADF polymer light‐emitting diodes.