Application of ion beam technology in modification of photoelectrode
2017
Semiconductor-based photoelectrolysis for water splitting to produce
hydrogen and oxygen is a simple, relatively cheap and reliable way
for energy utilization. Therefore, developing photoelectrode materials
with high solar-to-hydrogen (STH) efficiency has become a hotspot
in the field of material science. Many semiconductor-based photoelectrolysis
suffer from the lack of visible light response and low charge separation
efficiency resulting in low photoelectrocatalytic activity. It is
particularly important to developing modified photoelectrode materials. Ion beam technology, as an important semiconductor modification
technology, has been generally used to modify the electronic property
of silicon. It has great potential application in modification of
photoelectrode materials. Comparing with traditional modification
method, ion beam technology has many advantages, such as good repeatability
and controllability. Ion beam technology is an effective method for
doping. Various ion species can be doped into photoelectrode materials.
The ion implantation process could ensure the uniformity and purity
of the introduced elements in materials. Doped ions can be highly
dispersed and present at the lattice positions deeply inside the film.
Basing on the works of our and other research groups, this review
briefly introduces the advantages, the recent progress, and the current
issues of application of ion beam technology in modifying photoelectrode
materials. Ion beam technology has been used to effectively improve visible
light absorption of many photoelectrode materials. TiO 2 doping through metal ion implantation has been studied since 1998.
Various metal ion implantations have been found to be effective in
improving material’s visible light response. Compared with
metal ion implantation, only few examples of nonmetal implantation
are known. Since 2005, N ion implantation was reported to be effective
to improve photoelectrochemical (PEC) properties of TiO 2 , ZnO, WO 3 . Ion implantation is proven to be effective
and reliable method of doping. In addition, a gradient distribution
of dopants along the vertical direction of materials would be formed.
The gradient distributed dopants not only enhance the visible light
absorption, but also introduce a homojunction which efficiently drives
photo-induced electrons and holes separation and transfers. Ion implantation
introduces lots of defects into materials. The defects always are
known as recombination sites of electrons and holes. Post-implantation
thermal annealing process is critical for PEC performance by eliminating
partial defects. However, defects introduced by ion implantation are
controllable. On the one hand, by low energy ion irradiation, surface
defect has formed under control in shallow zone of photoelectrode.
Through defect engineering, the electronic structure of many semiconductors
can be modified. An impressive promotion of electrical conductivity
and more exposed of active sites can lead to remarkable enhancements
in photoelectrocatalytic performance. On the other hand, by high fluence
beam irradiation combination with thermal annealing, the irradiation
damage can be used to form nanostructure like nanorods. Up to now, the application of ion beam technology in modifying
photoelectrode materials is still at the comparatively primary stage.
In order to achieve high performance photoelectrochemical water splitting
using ion beam technology, more attention should be paid to the more
precise control over the dopants and defects. A large number of more
systematic and in-depth researches should be carried out.
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