The Fabrication of an Upright‐Standing Zinc Oxide Nanosheet for Use in Dye‐Sensitized Solar Cells

Abstract

Zinc oxide, an n-type semiconductor with a direct bandgap of 3.3 eV, has attracted interest from many academic and industrial researchers due to its wide array of applications in the design of chemical sensors, [1] photocatalysts, [2] phosphors, [3] and dye-sensitized solar cells. [4,5] In particular, ZnO has attracted attention as a fascinating alternative to TiO 2 in dyesensitized solar cells (DSCs) based on recent reports that demonstrated that ZnO and TiO 2 exhibit a similar electroninjection process from excited dyes in DSCs. [6,7] In these reports, ZnO showed a higher electronic mobility, making it more desirable. In order to improve physical and chemical performance in devices, designing the morphology of ZnO into rods, [8] columns, [9] and hierarchical structures [10] is now focus of current research. Control of crystal growth for these purposes can be conducted by chemical-bath deposition (CBD), in which the small degree of supersaturation of the solutions causes the heterogeneous nucleation of the metal oxide on substrates.[11] The solubility of solutes can change as a result of chemical reactions in solutions. When the solution reaches supersaturation, solid particles are formed through nucleation and crystal growth. The degree of supersaturation, S, is defined by the ratio of solute concentration in the supersaturated solution (C: C ³ C s ) to that of the saturated solution (C s ), C/C s . At lower degrees of supersaturation (in this case, S is near 1.0) heterogeneous nucleation on foreign surfaces is preferred over homogeneous nucleation in solution.Recently, the novel control of the morphology of zinc oxides through nanosheet or rod-like metal hydroxides have been studied. [12,13] The pyrolysis of nanostructured metal hydroxides results in nanostructured metal oxides without microstructural deformation. The resultant films have larger surface areas than those of traditional films that are fabricated by controlling the crystal growth process of ZnO. This is because single-crystal ZnO has a small surface area due to flat surfaces at the atomic level. We have previously reported the fabrication of nanoparticulate porous metal oxide and oxyfluoride films by the pyrolysis of layered metal hydroxides (LMHs) deposited in chemical baths.[14±16] The metal oxide films thus prepared consisted of secondary sheet-like particles, which were found to be an assembly of nanoparticles and nanopores. However, the crystal growth pattern of LMHs is generally limited to two-dimensions. This is different from the conventional crystal growth of ZnO, which has a wide variety of growth patterns, as mentioned above. The critical energy barrier for heterogeneous nucleation is smallest when the nuclei/substrate interfacial energy is at a minimum. On smooth surfaces, such as glass, it is believed that the lowest interfacial energy is attained when the lowest energy plane of the nuclei faces parallel to the substrate surface. [17] Hence, the LMHs' nuclei would have a sheet-like morphology and grow parallel to the substrate....

Ultrathin SnO2 Nanosheets: Oriented Attachment Mechanism, Nonstoichiometric Defects, and Enhanced Lithium-Ion Battery Performances

“…The electrode consisted of active material (SnO 2 ), conductivity agent (acetylene black, Alfa Aesar), and polymer binder (poly(vinylidene difluoride), 4 , which was explicitly revealed by XRD (see Supporting Information, Figure S1). This XRD result indicated that, at ambient condition, the precursor SnCl 2 mainly transformed into poorly crystallized Sn 6 4 . 52,53 However, the addition of NH 3 ·H 2 O quite favored this transition judging from the severe darkening of suspension color (from white to dark yellow-white), thus leading to higher yield of Sn 6 O 4 (OH) 4 .…”

One-dimensional ZnO nanostructures: Solution growth and functional properties

“…In this regard, studies on nanotubes [455,456], nanoparticle/nanowire composites [453,[457][458][459][460], hierarchical [199,461] structures [209,[462][463][464], and different growth parameters [465] have been shown to give several-fold increases in efficiency (Fig. 56(b)).…”

Development of nanostructure control process in the solution for application to energy and environmental fields

“…The DSC using the ZnO and Eosin Y as the dye indicated the conversion efficiency of 2%. 10) The oriented ZnO nanosheet film 15) was fabricated thorough the oriented layered hydroxide zinc carbonate nanosheet film by self-template method as shown in Fig. 3(b).…”