Single-Crystalline Protrusion-Rich Indium Tin Oxide Nanoparticles with Colloidal Stability in Water for Use in Sustainable Coatings

Abstract

Indium tin oxide (ITO) nanoparticles (NPs) with protrusions on their surfaces have been successfully obtained by solvothermal synthesis under high In3+ and Cl– concentrations. High-resolution transmission electron microscopy (HR-TEM) observations revealed that the ITO NPs with protrusions consisted of not a polycrystalline but a single-crystalline structure. The results suggested that the unique shape was produced by heterogeneous epitaxial nucleation on the growing surfaces of the ITO NPs in the presence of tetramethylammonium hydroxide (TMAH). Inhibition of homogeneous particle growth by adsorption of a large excess amount of Cl– ions on the surfaces of growing ITO NPs might play a critical role in the evolution of the unique protrusions. Compared to single-crystalline ITO NPs with a cubic shape, the ITO NPs thus obtained showed a high specific surface area and a low resistivity. Furthermore, the ITO NPs with protrusions exhibited an unprecedented high dispersion stability in water for a long period without the use of any dispersant. 1H nuclear magnetic resonance (NMR) relaxation (T 2) measurements revealed that such high dispersion stability could be due to the shape-triggered increase in the hydrophilicity of the surfaces of the ITO NPs. The resulting ITO NP dispersions in water could be applied to prepare ITO thin films with low resistivity on a glass substrate. The behavior has great potential for application as sustainable coating materials to fabricate transparent conductive ITO thin films on flexible substrates under mild atmospheric conditions without usage of expensive production systems and harmful and environmentally undesirable chemicals.

A Nanoparticle-Mist Deposition Method: Fabrication of High-Performance ITO Flexible Thin Films under Atmospheric Conditions

“…Both water dispersions of C1 and P1 contain no organic dispersants, and the fundamental difference between C1 and P1 is the shape-induced dispersion stability in water over a long period. [41] The SEM images in Figure 5b revealed that the surface state of the C1-based thin lm was totally different from that of the corresponding P1-based thin lm. Rough and porous structures were clearly observed in Figure 5b.…”

“…The details of the preparation of C1 and P2 are summarized in the following Methods section (for P1, see ref. 41). Figure 1a (i), (ii), and (iii) shows the X-ray diffraction (XRD) patterns of C1, P1, and P2, respectively.…”

“…These results strongly prompted us to use TCO NPs with low resistivity, which might emphasize the advantages of the deposition method because a heat-treatment-less process is readily applicable to the preparation of TCO thin lms on exible lms under atmospheric conditions. For the TCO NPs, we recently reported that solvothermally prepared single-crystalline cubic-shaped [38][39][40] and protrusion-rich indium tin oxide (ITO) [41] NPs show low resistivity. The electrical resistivity of the powder compacts of the ITO NPs with protrusions under an applied pressure of 20 kN was 1.98 x 10 -2 Ω•cm.…”

“…The electrical resistivity of the powder compacts of the ITO NPs with protrusions under an applied pressure of 20 kN was 1.98 x 10 -2 Ω•cm. [41] Furthermore, compared with the ITO NPs with a cubic shape, [38][39][40] the ITO NPs with protrusions on their surfaces demonstrated unprecedented high water dispersion stability without adding dispersants such as surfactants. This property might be positively applicable to the mist deposition method using water dispersions of ITO NPs.…”

Indium Oxide Based Nanomaterials: Fabrication Strategies, Properties, Applications, Challenges and Future Prospect

“…Different indium oxide based bulk nanomaterials have been synthesized by solvothermal/hydrothermal method. In this regard, Suzuki et al [54] synthesized indium tin oxide nanoparticles via solvothermal method for sustainable coating application.…”