Crystalline TiO2: A Generic and Effective Electron-Conducting Protection Layer for Photoanodes and -cathodes

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• 作者：Bastian Mei ; Thomas Pedersen ; Paolo Malacrida ; Dowon Bae ; Rasmus Frydendal ; Ole Hansen ; Peter C. K. Vesborg ; Brian Seger ; Ib Chorkendorff
• 刊名：Journal of Physical Chemistry C
• 出版年：2015
• 出版时间：July 9, 2015
• 年：2015
• 卷：119
• 期：27
• 页码：15019-15027
• 全文大小：540K
• ISSN：1932-7455

文摘

Stabilizing efficient photoabsorbers for solar water splitting has recently shown significant progress with the development of various protection layers. Suitable protection layers for tandem devices should be conductive, transparent, and stable in strongly acidic or alkaline solutions. This paper shows that under certain conditions n-type semiconductors, such as TiO₂, can be used as protection layers for Si-based photoanodes. It also provides evidence that even in a photoanode assembly TiO₂ is conducting only electrons (not holes as in p-type protection layers), and therefore TiO₂ can be described as a simple ohmic contact. This renders n-type semiconductors, such as TiO₂, to be versatile and simple protection layers, which can be used for photoanodes and as previously shown for photocathodes. The ohmic behavior of n-type TiO₂ in a Si/TiO₂鈥損hotoanode assembly is demonstrated under dark and illuminated conditions by performing the oxygen evolution reaction (OER) and using the Fe(II)/Fe(III) redox couple. These measurements reveal that the performance of the Si/TiO₂鈥損hotoanode assembly is strongly dependent on the TiO₂/electrolyte interaction. Finally, the conditions and requirements that make TiO₂ generally applicable for photoanode assemblies, and thus for protecting tandem devices, are outlined and quantitatively shown by band diagram calculations. The results presented here provide the understanding required for the design of highly efficient and stable photoelectrochemical water splitting devices.