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

Author(s): Keyan Bai ¹ ^, ² ^, ³ ^, ⁴ ^, ⁵ , Shumeng Wang ¹ ^, ² ^, ³ ^, ⁴ ^, ⁵ , Lei Zhao ¹ ^, ² ^, ³ ^, ⁴ ^, ⁵ , Junqiao Ding ¹ ^, ² ^, ³ ^, ⁴ ^, ⁵ , Lixiang Wang ¹ ^, ² ^, ³ ^, ⁴ ^, ⁵

Publication date (Electronic): 2017

Journal: Polymer Chemistry

Publisher: Royal Society of Chemistry (RSC)

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Abstract

By fully replacing the alkyloxy side chain with a carbazole, a highly emissive homopolymer P(Cz-SF) is developed for deep-blue PLEDs.

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.

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Multi-colour organic light-emitting displays by solution processing.

C. David Müller, Aurélie Falcou, Nina Reckefuss … (2003)

Organic light-emitting diodes (OLEDs) show promise for applications as high-quality self-emissive displays for portable devices such as cellular phones and personal organizers. Although monochrome operation is sufficient for some applications, the extension to multi-colour devices--such as RGB (red, green, blue) matrix displays--could greatly enhance their technological impact. Multi-colour OLEDs have been successfully fabricated by vacuum deposition of small electroluminescent molecules, but solution processing of larger molecules (electroluminescent polymers) would result in a cheaper and simpler manufacturing process. However, it has proved difficult to combine the solution processing approach with the high-resolution patterning techniques required to produce a pixelated display. Recent attempts have focused on the modification of standard printing techniques, such as screen printing and ink jetting, but those still have technical drawbacks. Here we report a class of electroluminescent polymers that can be patterned in a way similar to standard photoresist materials--soluble polymers with oxetane sidegroups that can be crosslinked photochemically to produce insoluble polymer networks in desired areas. The resolution of the process is sufficient to fabricate pixelated matrix displays. Consecutive deposition of polymers that are luminescent in each of the three RGB colours yielded a device with efficiencies comparable to state-of-the-art OLEDs and even slightly reduced onset voltages.