Fluorene-carbazole-based hyperbranched polymers with linear red TADF chromophores for high-efficiency white and red electroluminescent devices

Abstract

Solution-processed polymer light emitting devices (PLEDs) using high-quality thermally activated delayed fluorescence (TADF) polymers as the emitting layers are attractive, however, high-efficiency white-light TADF polymers are very rare because of the complicated radiative transition channels. In this study, a series of hyperbranched TADF conjugated polymers were designed and synthesized which adopted the linear D-A-type TADF emitter of 1,8-naphthalimide-acridine as red chromophores, conjugated poly(fluorene-carbazole) as the blue backbone and triphenylamine as the hyperbranched cores. By adjusting the appropriate feed ratios of monomers, energy transfer process from the blue backbone to the red chromophores could be regulated and HR0.8 film had the highest photoluminescent quantum yield of 24%. Consequently, its doped electroluminescent device showed the cold-white emission with the CIE color coordinates of (0.35, 0.23) and the maximum EQE of 6.82%. By simply raising the concentration of the red chromophore in the polymers, the rapid reverse intersystem crossing (RISC) process and the enlarged energy gap between S1 and T1 were achievable.