Nanoforest of Hydrothermally Grown Hierarchical ZnO Nanowires for a High Efficiency Dye-Sensitized Solar Cell

Abstract

In this paper, in order to increase the power conversion efficiency we demonstrated the selective growth of "nanoforest" composed of high density, long branched "treelike" multigeneration hierarchical ZnO nanowire photoanodes. The overall light-conversion efficiency of the branched ZnO nanowire DSSCs was almost 5 times higher than the efficiency of DSSCs constructed by upstanding ZnO nanowires. The efficiency increase is due to greatly enhanced surface area for higher dye loading and light harvesting, and also due to reduced charge recombination by providing direct conduction pathways along the crystalline ZnO "nanotree" multi generation branches. We performed a parametric study to determine optimum hierarchical ZnO nanowire photoanodes through the combination of both length-wise growth and branched growth processes. The novel selective hierarchical growth approach represents a low cost, all solution processed hydrothermal method that yields complex hierarchical ZnO nanowire photoanodes by utilizing a simple engineering of seed particles and capping polymer.

One-dimensional ZnO nanostructures: Solution growth and functional properties

“…The growth mechanism was proposed to involve their effect on the solution pH and coordination with Zn 2+ [198]. Similar secondary nucleation on the ZnO nanowire side surfaces has also recently been demonstrated by coating with another round of seed nanoparticles [199]. Since the diaminopropane molecules combine with water molecules and release hydroxide ions, the preferred adsorption of the diaminopropane molecules on the nanowire side surfaces is expected to raise the local pH value, which assists the formation of the first a few layers of ZnO clusters near the side surfaces.…”

“…[18]. (b) J-V curves of a DSSC based on hierarchical ZnO nanowire "nano-forest" with increasing lengthwise growth (LG) and branched growth (BG) [199]. Reproduced with permission…”

“…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)).…”

Electrical, photoelectrical and morphological properties of ZnO nanofiber networks grown on SiO2 and on Si nanowires

“…ZnO nanofiber networks (NFNs) have been of interest in recent years due to their potential in future technological applications [1][2][3][4][5][6][7] . ZnO is a n-type semiconductor with a direct wide band gap of 3.37 eV (UV), large exciton binding energy (60 meV), high superficial reactivity and high Curie temperature (with magnetic doping).…”

Facile and Surfactant-Free Synthesis of Hierarchical ZnO Microstructures

“…These applications result from its unique properties, which depend not only on the phase but also on the morphology and organization. For instance, Ko et al reported that ZnO nanowires present high efficiency in dye-sensitized solar cells [8]. Arya et al demonstrated that ZnO crystals exhibit different biosensor properties corresponding to their different shape changes [9].…”