Heterojunctionphotoelectrode is a hot research topic for solar energy conversion. Commonly,the bulk energy band structure is under prior consideration for heterojunctiondesign, to favour the charge transfer process. However, since the charge transferonly takes place over several atomic plans at the hetero-interfaces, thephotovoltaic behavior of these photoelectrodes sensitively varies under theinfluence of interfacial energetics. But until now, there is still lack of someclear understanding on the charge separation and transport process throughthe multiple interfacial energy levels involved in the heterojunctions. Herethe primary question is how to efficiently manipulate these energy levels.
In this paper, an n-Si Schottky photoanode with high water oxidationperformance is achieved through effective manipulation of interfacialenergetics. The undesired donor-like interfacial defects and its adverseeffects on charge transfer in n-Si/ITO are well recognized and diminishedthrough the treatment on interfacial electronic states. The obtained n-Si/TiOx/ITOSchottky junction exhibits a highly efficient charge transport and a barrierheight as high as 0.95 eV, the maximum reported so far for water-splitting n-Siphotoanodes. Then, the holes extraction can be further facilitated through thevariation of surface energy level, with the NiOOH coated ITO layer. This isconfirmed by a 115% increase in surface photovoltage of the photoanode.Eventually, the n-Si/TiOx/ITO/NiOOH photoanode shows anunprecedented low onset potential of 0.9 V (vs. RHE) for water oxidation amongn-Si photoanodes. Meanwhile, a charge separation efficiency up to 100% and aninjection efficiency greater than 90% at a wide voltage rang are also realizedfor water oxidation reaction.
This study clearly illustrates the importance and feasibility of such aninterfacial energetics strategy in enhancing the PEC behavior of a Schottkyphotoanode. The strategy developed in this work is not only adapt to thephotoanode with Si as the absorber, but also can be applied to the photoanodesystems with other semiconductors.
This workwas financially supported by 973 National Basic Research Program of theMinistry of Science and Technology (No. 2014CB239403), National Natural ScienceFoundation ofChina (No. 21401189 and 21573230), and the 56th Class GeneralFinancial Grant from China Postdoctoral Science Foundation (No. 2014M561258).(Textand Imaged by Can Li and Tingting Yao)
