Copolyfluorene containing 4,4′-bis[4-(di-p-tolylamino)styryl]biphenyl as chromophore for efficient blue polymer light-emitting diodes

Abstract

High-efficiency blue polymer light-emitting diodes (PLEDs) remain elusive, especially in simple architectures. To address this, we developed a series of copolyfluorenes by incorporating a benchmark chromophore and a charge-transport unit into a poly(9,9-dioctylfluorene) backbone. The single-layered PLED based on PF-DPAVBi0.5 containing 0.5 mol% 4,4’-bis[4-(di-p-tolylamino)styryl]biphenyl (DPAVBi) units exhibited the highest luminous efficiency (LE) of 6.62 cd A⁻¹, associated with an external quantum efficiency (EQE) of 4.78% and a Commission Internationale de l’Eclairage (CIE) coordinates of (0.15, 0.17). The DPAVBi units function not only as a chromophore to stabilize the electroluminescence spectra but also as charge transport sites. Notably, increasing the DPAVBi content to 1 mol% in PF-DPAVBi1 tuned the recombination zone, resulting in significantly suppressed efficiency roll-off (with a decrease of only 6.8% at 1000 cd m⁻²). This work demonstrates that rational copolymer design is a powerful strategy for enhancing the performance and stability of polyfluorene-based blue emitters, positioning these materials as highly promising for low-cost, high-performance PLEDs.