Heterojunction photoelectrode is a hot research topic for solar energy conversion. Commonly, the bulk energy band structure is under prior consideration for heterojunction design, to favour the charge transfer process. However, since the charge transfer only takes place over several atomic plans at the hetero-interfaces, the photovoltaic behavior of these photoelectrodes sensitively varies under the influence of interfacial energetics. But until now, there is still lack of some clear understanding on the charge separation and transport process through the multiple interfacial energy levels involved in the heterojunctions. Here the primary question is how to efficiently manipulate these energy levels.
Our group achieved an n-Si Schottky photoanode with high water oxidation performance through effective manipulation of interfacial energetics. The undesired donor-like interfacial defects and its adverse effects on charge transfer in n-Si/ITO are well recognized and diminished through the treatment on interfacial electronic states. The obtained n-Si/TiOx/ITO Schottky junction exhibits a highly efficient charge transport and a barrier height as high as 0.95 eV, the maximum reported so far for water-splitting n-Si photoanodes. Then, the holes extraction can be further facilitated through the variation of surface energy level, with the NiOOH coated ITO layer. This is confirmed by a 115% increase in surface photovoltage of the photoanode. Eventually, the n-Si/TiOx/ITO/NiOOH photoanode shows an unprecedented low onset potential of 0.9 V (vs. RHE) for water oxidation among n-Si photoanodes. Meanwhile, a charge separation efficiency up to 100% and an injection efficiency greater than 90% at a wide voltage rang are also realized for water oxidation reaction.
This study clearly illustrates the importance and feasibility of such an interfacial energetics strategy in enhancing the PEC behavior of a Schottky photoanode. The strategy developed in this work is not only adapt to the photoanode with Si as the absorber, but also can be applied to the photoanode systems with other semiconductors. It is also the subsequent study of silicon in PEC water splitting (ChemSusChem, 2015,DOI:10.1002/cssc.201501004 ) carried by our group.
The related results were published in the journal of J. Am. Chem. Soc. (DOI: 10.1021/jacs.6b07188)This work was financially supported by 973 National Basic Research Program of the Ministry of Science and Technology (No. 2014CB239403), National Natural Science Foundation of China (No. 21401189 and 21573230), and the 56th Class General Financial Grant from China Postdoctoral Science Foundation (No. 2014M561258). (Text and Imaged by Tingting Yao).
