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Publications (2)16.89 Total impact

  • Jonghun Lee · Melissa A. Petruska · Shouheng Sun
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    ABSTRACT: In a solution-phase synthesis of nanocrystals (NCs), organic surfactants play an important role in size and shape control as well as in facilitating the stable dispersion of NCs in solvents. However, in order to use these NCs for electrical applications, the surfactants must be removed effectively. Here we report that monodisperse indium tin oxide (ITO) NCs were synthesized and stabilized with oleate/oleylamine ligands, and these long-chain surfactants were readily substituted with tetrabutylammonium hydroxide (TBAOH), forming a stable methanol dispersion. Uniform assemblies of ITO NCs were made by spin-coating the ITO–TBAOH NC dispersions with an assembly thickness controllable from 68 to 260 nm by the NC solution concentration. An annealing treatment at 120 °C and 300 °C under Ar + 5% H2 for 1 h effectively removed the TBAOH, and the ITO NC assemblies showed high transparency (>88%) and low resistivity (2.6 × 10–3 Ω·cm). Our new approach to surface modification of ITO NCs with a volatile surfactant followed by film deposition is an effective strategy for fabricating ITO NC films by a solution process with desired transparency and conductivity for transparent electrode applications.
    No preview · Article · May 2014 · The Journal of Physical Chemistry C
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    Jonghun Lee · Sunghwan Lee · Guanglai Li · Melissa A Petruska · David C Paine · Shouheng Sun
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    ABSTRACT: Monodisperse 11 nm indium tin oxide (ITO) nanocrystals (NCs) were synthesized by thermal decomposition of indium acetylacetonate, In(acac)(3), and tin bis(acetylacetonate)dichloride, Sn(acac)(2)Cl(2), at 270 °C in 1-octadecene with oleylamine and oleic acid as surfactants. Dispersed in hexane, these ITO NCs were spin-cast on centimeter-wide glass substrates, forming uniform ITO NC assemblies with root-mean-square roughness of 2.9 nm. The assembly thickness was controlled by ITO NC concentrations in hexane and rotation speeds of the spin coater. Via controlled thermal annealing at 300 °C for 6 h under Ar and 5% H(2), the ITO NC assemblies became conductive and transparent with the 146 nm-thick assembly showing 5.2 × 10(-3) Ω·cm (R(s) = 356 Ω/sq) resistivity and 93% transparency in the visible spectral range--the best values ever reported for ITO NC assemblies prepared from solution phase processes. The stable hexane dispersion of ITO NCs was also readily spin-cast on polyimide (T(g) ~360 °C), and the resultant ITO assembly exhibited a comparable conductivity and transparency to the assembly on a glass substrate. The reported synthesis and assembly provide a promising solution to the fabrication of transparent and conducting ITO NCs on flexible substrates for optoelectronic applications.
    Full-text · Article · Jul 2012 · Journal of the American Chemical Society