Flexible zinc oxide nanoparticle–multi charged conjugated electrolytes thin films for flexible optoelectronic devices
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초록
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We report that the flexibility of a zinc oxide nanoparticle (ZnO NP) thin film is improved by ionic interaction between ZnO NPs and multi-charged conjugated electrolytes. Intermixing of ZnO NPs (10~15 nm in diameter) and conjugated electrolytes, diphenylfluorene pyridinium bromide derivative (PFP:Br), enables the bromide anions to coordinate the zinc cations on the ZnO NP surfaces. The multi-charged cations with the ammonium-functionalized side chains can hold the bromide-chelated ZnO NPs adjacent to the ammonium cations by ionic interaction of N+–Br– ion pairs, confirmed by X-ray photoelectron spectroscopy (XPS) measurements. As a result, the 500-nm-thick ZnO NP–PFP:Br thin films show improved flexibility with a crack onset bending radius as low as 3 mm, compared to the ZnO NP thin films. Our results provide a facile strategy to improve the mechanical properties of the ZnO NP thin films and will facilitate the development of highly reliable flexible organic optoelectronic devices.