ZnO Nanosheets with Ordered Pore Periodicity via Colloidal Crystal Template Assisted Electrochemical Deposition

Abstract

The development of novel nanostructured materials with controlled shapes and ordered morphology has stimulated great research interest for seeking novel properties and tailorable functions. In particular, nanostructured ZnO, a remarkable semiconducting oxide with a broad, direct bandgap, received much attention for its potential applications such as UV lasing, electro-optical switches, chemical sensors, photocatalysts, and dye-sensitized solar cells. A series of ZnO nanostructures, such as nanowires, [1][2][3][4] nanorod arrays, [3,[5][6][7] nanobelts, [8] nanoneedle arrays, [9] nanorings, [10] and nanosheets [11,12] have been successfully synthesized. Recently, Eiji et al. [12] reported that ZnO films formed with upright standing nanosheets on substrates induce a very high conversion efficiency for dye-sensitized solar cells because of the easy diffusion of electrolytes in the direction perpendicular to the substrates. However, because the diffusion of electrolytes in the direction parallel to the substrate is still difficult in the nanosheet films, the conversion efficiency would further increase if the nanosheet was macroporous. On the other hand, nanosheets with ordered pore periodicity have a wide range of potential applications including photonic crystals, [13] nanosieve filters, [14,15] masks, [16] and catalysts. [17] Moreover, the modulation induced by both nanoscale thickness and periodic macroporous structure may result in more exciting properties, for example, subwavelength imaging by a photonic-crystal slab.[18]The 3D colloidal crystal template technique is one of the most versatile and efficient techniques for creating 3D periodic macroporous structures, such as inverse opals. [19][20][21][22] However, the fabrication of 2D ordered pore periodicity in a nanosheet whose direction is nearly vertical to the substrate using this method has not been reported. Here, we extend the colloidal crystal template technique to assist the electrochemical deposition of ZnO nanosheet structures and, thus, create 2D hexagonal pore periodicity on nanosheets. Indium tin oxide (ITO) coated glass is used as an electrochemical deposition working electrode. The synthetic polystyrene colloidal crystals are coated onto the ITO glass as templates. ZnO nanosheets with ordered pore periodicity are obtained by the electrochemical deposition of zinc hydroxide nitrate hydrate (ZHNH) into the interstices of colloidal-crystal arrays and the subsequent removal of the templates under calcination. The spatial arrangement of ZnO nanosheets with ordered pore periodicity on ITO substrates is largely affected by the colloidal crystal template assisted crystallization process. Figure 1a shows a scanning electron microscopy (SEM) image of the cross section of a colloidal crystal template that was made from polystyrene microspheres with a diameter of 270 nm on an ITO substrate. The colloidal crystal microspheres have a high degree of order in all directions on the substrate. The thickness of the microsphere arrays is estimated to be 6-7 lm, co...

ZnO Nanostructures for Dye‐Sensitized Solar Cells

“…REVIEW www.advmat.de result in many particular behaviors in electron transport or light propagation in view of the surface effect, quantum-confinement effect, or photon localization. [49][50][51] Those nanostructural forms of ZnO developed during the past several decades mainly include nanoparticles, [52,53] nanowires (or nanorods), [54,55] nanotubes, [56] nanobelts, [57] nanosheets, [54,58] and nanotips. [34,38] The production of these structures can be achieved through sol-gel synthesis, [53] hydrothermal/solvothermal growth, [54] physical or chemical vapor deposition, [55,57] low-temperature aqueous growth, [56,59] chemical bath deposition, [60] or electrochemical deposition.…”

“…[34,38] The production of these structures can be achieved through sol-gel synthesis, [53] hydrothermal/solvothermal growth, [54] physical or chemical vapor deposition, [55,57] low-temperature aqueous growth, [56,59] chemical bath deposition, [60] or electrochemical deposition. [58,61,62] In this article, recent developments in ZnO nanostructures, particularly for application in DSCs, are reviewed. It will show that photoelectrode films with nanostructured ZnO can significantly enhance solar-cell performance by offering a large surface area for dye adsorption, direct transport pathways for photoexcited electrons, and efficient scattering centers for enhanced light-harvesting efficiency.…”

Compact Inverse‐Opal Electrode Using Non‐Aggregated TiO2 Nanoparticles for Dye‐Sensitized Solar Cells

“…[3,13,14] In conjunction with these efforts, recent studies on photoelectrodes have expanded the processing strategies by using periodic nanostructures with long-range ordering to better assure an interconnected morphology of the TiO 2 structure. Such periodic structures have shown promising results for wide bandgap semiconductor materials, [15][16][17][18][19][20][21] core-shell structures, [22,23] nanowire (nanotube) structures, [6][7][8][9][10][11][24][25][26] and inverse-opal (IO) structures. [27][28][29][30][31][32][33] In particular, ordered IO structures of two-dimensional or threedimensional (2D or 3D) colloidal crystals have been successfully utilized in the modification of the absorption bands of dye sensitizers due to the photonic bandgap effect in DSSCs.…”

Template-based syntheses for shape controlled nanostructures

“…Once the polystyrene was removed afterwards, a highly ordered two-dimensional metallic nanostructure remained. This methodology has been successfully reproduced using other metals, metal oxides, and semiconducting materials such as Au [275], Co 3 O 4 [276], ZnO [277], MnO [278], CdSe [279], and V 2 O 5 [280]. With other two-dimensional structure promoting templates, such as graphene or carbon nanotubes, unusual two-dimensional nanostructures such as Mn nanoflowers [281], ZnO nanoflowers [282], and Co 3 O 4 nanoflakes [283] can also be produced through electrodeposition.…”