Abstract
Titanium dioxide (TiO2) nanotubes with vertically aligned array structures show substantial advantages in solar cells as an electron transport material that offers a large surface area where charges travel linearly along the nanotubes. Integrating this one-dimensional semiconductor material with plasmonic metals to create a three-dimensional plasmonic nanodiode can influence solar energy conversion by utilizing the generated hot electrons. Here, we devised plasmonic Au/TiO2 and Ag/TiO2 nanodiode architectures composed of TiO2 nanotube arrays for enhanced photon absorption, and for the subsequent generation and capture of hot carriers. The photocurrents and incident photon to current conversion efficiencies (IPCE) were obtained as a function of photon energy for hot electron detection. We observed enhanced photocurrents and IPCE using the Ag/TiO2 nanodiode. The strong plasmonic peaks of the Au and Ag from the IPCE clearly indicate an enhancement of the hot electron flux resulting from the presence of surface plasmons. The calculated electric fields and the corresponding absorbances of the nanodiode using finite-difference time-domain simulation methods are also in good agreement with the experimental results. These results show a unique strategy of combining a hot electron photovoltaic device with a three-dimensional architecture, which has the clear advantages of maximizing light absorption and a metal–semiconductor interface area.
Highlights
Plasmonic energy conversion has been studied extensively as an effective pathway for converting solar energy to current in comparison with typical electron–hole generation in semiconductor devices
We report the electrochemical preparation of titanium dioxide nanotubes (TNA) with various porosities by controlling the voltage during anodization as well as the fabrication of a Schottky diode to investigate the dependence of plasmonic behavior on the size and shape of the plasmonic material in the visible region for hot electron generation
The interface of the Au and TiO2 is the active area of the diode; hot electrons can be generated in the plasmonic Au and these hot electrons can overcome the Schottky barrier (ESB) and reach to the semiconductor material
Summary
Plasmonic energy conversion has been studied extensively as an effective pathway for converting solar energy to current in comparison with typical electron–hole generation in semiconductor devices. Designed nanostructures exhibit a localized surface plasmon resonance (LSPR) in which free electrons oscillate in resonance with the incident light, establishing electromagnetic fields that are highly localized This efficient light trapping in plasmonic nanostructures can be coupled with semiconductor devices for photovoltaic applications[1,2]. The one-dimensional nanostructure exhibits fascinating properties and attractive performance because of its large surface area upon which various chemical reactions occur and the direct orthogonal electron path through the tubular walls that results in efficient charge transport in photoanodes[43] Despite these motivating properties, in general, the primary drawback of TiO2 is its transparency in visible light. Plasmonic nanostructures act as an antenna to capture the incoming light with minimal reflection These plasmonic structures generate hot electrons through the decay process that occurs transverse across the semiconductor material, contributing to the photocurrent. Further improvements of the diode efficiency can be attained to explore the fields of solar cells and photocatalysis
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