Recent discoveries have demonstrated ample opportunities for engineering the surface chemistry of nanocrystals, extending beyond traditional ligands to include small molecules and inorganic compounds. This surface chemistry can be used to control properties including solubility, superlattice spacing, conductivity, electronic structure, and more. Here, we explore the effect of different surface chemistries on the behavior of nanocrystal inks. An ink typically utilizes colloidal suspensions of nanocrystals which, upon annealing, sinter to form larger polycrystalline grains, surrendering their nano-scale properties. Applications encompass sensors, displays, photovoltaics, and other optoelectronic devices. In such systems, a desirable ligand should control surface reactivity between nanocrystals, leave no residue after annealing, and maintain solubility of the ink during film preparation. We employ both inorganic and organic sulfur-based ligands including ammonium sulfide and alkyl thiols the surface of tin sulfide and zinc sulfide nanocrystals and analyze their effect on thin film formation. The efficacy of these ligands is measured in exchange efficiency as well as the morphological, structural, optical, and electronic properties of the resulting thin films. Sulfur-based ligands are shown to enhance the thin film quality including increases in grain size and purer compositions while maintaining optical integrity. We demonstrate a strong correlation between these properties and the surface chemistry employed, and suggest further improvements for nanocrystal inks.

Role of sulfur-based nanocrystal ligands in metal chalcogenide nanocrystal inks

248th National Meeting (2014)

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