Highly efficient and stable blue polymer light emitting diodes based on polysilafluorenes with pendent hole transporting groups

Abstract

Two homopolymers of triphenylamine and carbazole grafting silafluorenes (PSF-TPA and PSF-Cz) were synthesized and their electroluminescence properties were investigated in this paper. Their carbon analog polyfluorenes with the same substituents were also prepared for comparison. Polysilafluorenes are found to have higher efficiencies and better color purities than the corresponding analog polyfluorenes. Among them, PSF-Cz was found to be a new promising blue-light emitter with an external quantum efficiency of ca. 4.1% and CIE coordinates of (0.16, 0.08), which is among the best deep blue emitters for polymer light-emitting diode (PLED) applications until now. Further study revealed that the silicon atom at the 9-position showed a strong σ conjugation effect and increased the oxidation potential of the final polymer as compared with PF-Cz. The DFT calculation also supports the experimental results. The carrier mobility measurements demonstrate that PSF-Cz has the highest hole mobility and well-balanced hole and electron carriers among them, corresponding to its highest EL efficiency.