Photoelectrochemical characteristics of ZnO/ TiO2 nanoheterojunctions

Fang Wang,Jun Dai,Dengji Yu

doi:10.1063/1.5090306

Abstract

In this paper, TiO2 nanotubes are fabricated on Ti foils by anodic oxidation, a layer of ZnO nanorod arrays is further deposited on the TiO2 nanotube without seed layer by a hydrothermal method at different Zn2+ concentration. The result shows that the ZnO nanorods mainly present needle-like structure and the density of the nanorods increases with the Zn2+ concentration. The PL of the ZnO nanorods show that there are defect levels formed in the ZnO nanorods. When the ZnO/TiO2 heterostructure is irradiated by the light, the photocurrent is significantly increased by about 2-3 times of that from pure TiO2 nanotubes. The band diagram of the ZnO/TiO2/Ti was proposed to interpret the photocurrent characteristics. Our result indicates that the ZnO/TiO2 can be excellent candidate semiconductor material for the photoelectrochemical energy transfer.

Highlights

One-dimensional (1-D) nanostructures have attracted tremendous attentions due to their excellent optoelectronic properties. 1-D semiconductor nanostructures usually have high surface-to-volume ratio, good carrier-directed migration path, low reflectivity, high light scattering and capture.4,5 Up to date, many kinds of 1-D semiconductor nanostructures have been reported, such as IV group Si and Ge nanorod,6,7 III-V group GaN-based and GaAs-based nanorod,8–10 II-VI group semiconductor (CdS,11 CdSe,12 CdTe,13 et al.), and oxide semiconductors.14 Among those oxide semiconductor nanostructures, oxide semiconductor TiO215 and ZnO16 present unique advantages in the photoelectrochemical anode material due to their good carrier transport
ZnO nanorods are successfully grown on TiO2 nanotubes by hydrothermal method without the assist of ZnO seed layer to improve photoelectrochemical properties
Compared to pure TiO2 nanotubes fabricated by anodic oxidation on Ti foils, ZnO/TiO2 heterostructure exhibits a higher photocurrent, indicating that the formation of ZnO/TiO2 heterojunction helps to improve photocurrent

Summary

INTRODUCTION

One-dimensional (1-D) nanostructures (such as nanowires, nanorods and nanotubes3) have attracted tremendous attentions due to their excellent optoelectronic properties. 1-D semiconductor nanostructures usually have high surface-to-volume ratio, good carrier-directed migration path, low reflectivity, high light scattering and capture. Up to date, many kinds of 1-D semiconductor nanostructures have been reported, such as IV group Si and Ge nanorod, III-V group GaN-based and GaAs-based nanorod, II-VI group semiconductor (CdS, CdSe, CdTe, et al.), and oxide semiconductors. Among those oxide semiconductor nanostructures, oxide semiconductor TiO215 and ZnO16 present unique advantages in the photoelectrochemical anode material due to their good carrier transport. Many kinds of 1-D semiconductor nanostructures have been reported, such as IV group Si and Ge nanorod, III-V group GaN-based and GaAs-based nanorod, II-VI group semiconductor (CdS, CdSe, CdTe, et al.), and oxide semiconductors.. Many kinds of 1-D semiconductor nanostructures have been reported, such as IV group Si and Ge nanorod, III-V group GaN-based and GaAs-based nanorod, II-VI group semiconductor (CdS, CdSe, CdTe, et al.), and oxide semiconductors.14 Among those oxide semiconductor nanostructures, oxide semiconductor TiO215 and ZnO16 present unique advantages in the photoelectrochemical anode material due to their good carrier transport. The photogenerated electron-hole pairs in TiO2 are easy to recombine, which shorten the life of holes and electrons and reduce efficient density of the carrier transport.. The underlying mechanism was discussed based on the band diagram of the heterojunctions

EXPERIMENTAL DETAILS

CONCLUSIONS