Hierarchical Nanowire Arrays Research Articles

Dye-sensitized solar cells based on a double layered TiO2 photoanode consisting of hierarchical nanowire arrays and nanoparticles with greatly improved photovoltaic performance

A novel double layered photoanode consisting of oriented hierarchical anatase TiO2 nanowire arrays (HNW) and nanoparticles (NP) has been successfully fabricated on a Ti-foil substrate via a two-step hydrothermal and screen-printing process, respectively. Compared to a NP based cell, the photovoltaic performance of the TiO2 HNW cell highlights several outstanding properties, including superior light scattering, rapid electron transport and lower electron recombination rate. Furthermore, the effect of the TiO2 NP film thickness (top layer) on the power conversion of the DSSCs has been investigated in detail. The DSSC based on a Ti/TiO2 HNW + NP photoelectrode with a total thickness of 31 μm (HNW: 13 μm; NP: 18 μm) shows the highest power conversion efficiency of 7.92%, which is remarkably higher than those of 13 μm HNW (4.52%), 18 μm NP (6.50%) and 31 μm NP (5.99%) photoelectrodes. The enhancement of the efficiency for the double layered photoanode based cell compared to the single NP is mainly attributed to better light scattering capability, faster electron transport and lower electron recombination for the former.

Electrochemical deposition of branched hierarchical ZnO nanowire arrays and its photoelectrochemical properties

Branched hierarchical ZnO nanowire arrays are synthesized on fluorine-doped tin oxide (FTO) substrate via a two-step electrochemical deposition process, which involves the electrodeposition of ZnO nanowire arrays on conductive glass substrate, followed by the electrochemical growth of ZnO nanorod branches on the backbones of the primary ZnO nanowires. The formation mechanism of the branched hierarchical nanostructure is discussed. It is demonstrated that coating the primary nanowire arrays with ZnO nanoparticles seed layer plays a key role in synthesising the branched hierarchical ZnO nanostructure. By adjusting the concentration of Zn(CH 3COO) 2 colloid in coating process and the reaction time of the second-step deposition, the density and the length of the secondary nanorod branches in the hierarchical nanostructures can be both varied. Moreover, the photoelectrochemical properties of the dye-sensitized solar cell (DSSC) based on branched hierarchical ZnO nanowire arrays are investigated. Due to the enlargement of the internal surface area within the branched nanostructure photoelectrode, the DSSC consisting of branched hierarchical ZnO nanowire arrays yields a power conversion efficiency of 0.88%, which is almost twice higher than that of the DSSC fabricated using bare ZnO nanowire arrays.

Different ZnO Nanostructures Fabricated by a Seed-Layer Assisted Electrochemical Route and Their Photoluminescence and Field Emission Properties

A simple seed-layer assisted electrochemical deposition (ECD) route has been successfully developed for preparation of different ZnO nanostructures, and their optical and field emission properties are also studied. ZnO films, nanowires, and nanosheets could be prepared in a rational way by just controlling the ECD current density. The corresponding growth mechanisms are also discussed on the basis of the characteristics of the ZnO crystal structure and the influences of the seed-layer and ECD current density. Except for ZnO nanosheets, both the room-temperature and low-temperature photoluminescence measurements of the ZnO films and nanowire arrays show strong ultraviolet excitonic emission, which proves their good crystal quality. Detailed analysis of the field emission (FE) properties indicates that the hierarchical ZnO nanowire array shows good FE property due to their high aspect ratio, small radius curvature, and proper density.

Large-Scale Hierarchical Organization of Nanowire Arrays for Integrated Nanosystems

The assembly of nanowires and nanotubes into arrays patterned on multiple length scales is critical to the realization of integrated electronic and photonic nanotechnologies. A general and efficient solution-based method for controlling organization and hierarchy of nanowire structures over large areas has been developed. Nanowires were aligned with controlled nanometer to micrometer scale pitch using the Langmuir−Blodgett technique and transferred to planar substrates in a layer-by-layer process to form parallel and crossed nanowire structures. The parallel and crossed nanowire structures were efficiently patterned into repeating arrays of controlled dimensions and pitch using photolithography to yield hierarchical structures with order defined from the nanometer through centimeter length scales. In addition, electrical transport studies show that reliable electrical contacts can be made to the hierarchical nanowire arrays prepared by this method. This solution-based process offers a flexible pathway for...

Nanolithography Using Hierarchically Assembled Nanowire Masks

A general and scalable method has been developed for patterning nanometer scale lines hierarchically over large areas using nanowires as masks for etching and deposition. Core−shell nanowires with controlled diameter and shell dimensions were aligned with nanometer to micrometer scale pitches using a Langmuir−Blodgett approach and then transferred en mass to planar substrates. Transferred nanowires were used as deposition masks to define metal lines with pitches from the nanometer to micrometer scale over centimeter square areas. Hierarchical parallel nanowire arrays were also prepared and used as masks to define nanometer pitch lines in 10 × 10 μm2 arrays repeated with a 25 μm array pitch over centimeter square areas. This nanolithography method represents a highly scalable and flexible pathway for defining nanometer scale lines on multiple length scales and thus has substantial potential for enabling the fabrication of integrated nanosystems.