Aligned ZnO/CdTe Core−Shell Nanocable Arrays on Indium Tin Oxide: Synthesis and Photoelectrochemical Properties

Abstract

Vertically aligned ZnO/CdTe core-shell nanocable arrays-on-indium tin oxide (ITO) are fabricated by electrochemical deposition of CdTe on ZnO nanorod arrays in an electrolyte close to neutral pH. By adjusting the total charge quantity applied during deposition, the CdTe shell thickness can be tuned from several tens to hundreds of nanometers. The CdTe shell, which has a zinc-blende structure, is very dense and uniform both radially and along the axial direction of the nanocables, and forms an intact interface with the wurtzite ZnO nanorod core. The absorption of the CdTe shell above its band gap ( approximately 1.5 eV) and the type II band alignment between the CdTe shell and the ZnO core, respectively, demonstrated by absorption and photoluminescence measurements, make a nanocable array-on-ITO architecture a promising photoelectrode with excellent photovoltaic properties for solar energy applications. A photocurrent density of approximately 5.9 mA/cm(2) has been obtained under visible light illumination of 100 mW cm(-2) with zero bias potential (vs saturated calomel electrode). The neutral electrodeposition method can be generally used for plating CdTe on nanostructures made of different materials, which would be of interest in various applications.

One-dimensional ZnO nanostructures: Solution growth and functional properties

“…It is possible to passivate the surface dangling bonds of ZnO nanowires by coating with other compound semiconductors, such as CdSe [19,211,212] and CdTe [213] by electrodeposition, CdS [214], SnO 2 [215], MgO [216,217], and ZrO [217] by hydrothermal reaction, Co 3 O 4 [218] by photochemical reaction, ZnS [219,220] by sulfidation, and Al 2 O 3 [221] and TiO 2 [222] by atomic layer deposition (ALD). In most cases, the asformed shell layers are polycrystalline or amorphous in nature.…”

“…(b) HRTEM image taken from the ZnO/CdTe interface region, showing the well-crystallized structure of the CdTe layer [213]. (c) Low magnification TEM image showing SnO 2 capping a ZnO nanowire with the nanowire tip exposed [215].…”

“…The traditional reaction conditions for fabricating CdTe are too stringent to allow the presence of ZnO nanowires [223][224][225][226]. Wang et al demonstrated the deposition of large-scale ZnO-CdTe core-shell nanowire arrays on indium-tin-oxide (ITO) substrates through a benign electrodeposition method (pH 8.3), which was compatible with the ZnO nanowires [213]. The electrodeposition was carried out with a threeelectrode system, with the ZnO nanowire array as the working electrode, a standard calomel electrode (SCE) as the reference electrode, and a Pt foil as the counter electrode.…”

“…22(b), after deposition, an intact interface was formed between the single crystal ZnO nanowire core and the high crystallinity CdTe shell. XRD results showed that the CdTe shell had a zinc-blende structure, and the crystallinity could be further increased by annealing [213].…”

Enhancement of the photoelectrochemical properties of Cl-doped ZnO nanowires by tuning their coaxial doping profile

“…8 Shells of lower band gap materials can extend the NW's core optical absorption to the visible part of the spectrum, thus promoting charge carrier photogeneration. 9 Nevertheless, the use of coaxial heterojunctions has the challenge of the lattice mismatch, which generally introduces a significant density of interface defects that can decrease the optoelectronic properties of the formed heterostructure.…”