Highly emissive carbazole-functionalized homopoly(spirobifluorene) for deep-blue polymer light-emitting diodes

Abstract

By fully replacing the alkyloxy side chain with a carbazole, we have designed and synthesized a highly emissive carbazole-functionalized homopoly(spirobifluorene) (denoted as P(Cz-SF)) for deep-blue polymer light-emitting diodes (PLEDs). Attributable to such a small variation of the molecular structure, the unwanted charge transfer from the pendant to the backbone can be effectively prevented in P(Cz-SF). Compared with the alkyloxy-tethered polymer P(RO-SF) (λ_PL = 455 nm, FWHM = 58 nm, Φ_PL = 0.20), P(Cz-SF) shows a blue-shifted emission of 422 nm accompanied by a narrower full width at half maximum (FWHM) of 45 nm and an improved photoluminescence quantum yield (PLQY) of 0.60 in solid films. As a consequence, a high-performance deep-blue device is realized for P(Cz-SF), revealing a state-of-the-art external quantum efficiency of 3.0% associated with Commission Internationale de L'Eclairage (CIE) coordinates of (0.17, 0.06). The results indicate that poly(spirobifluorene) with a carbazole as the side chain instead of alkyloxy will be a promising platform to develop efficient deep-blue emitters used for PLEDs.