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From Geometry to Activity: A Quantitative Analysis of WO 3 /Si Micropillar Arrays for Photoelectrochemical Water Splitting
Author(s) -
Zhao Yihui,
Westerik Pieter,
Santbergen Rudi,
Zoethout Erwin,
Gardeniers Han,
BieberleHütter Anja
Publication year - 2020
Publication title -
advanced functional materials
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 6.069
H-Index - 322
eISSN - 1616-3028
pISSN - 1616-301X
DOI - 10.1002/adfm.201909157
Subject(s) - photocurrent , materials science , pillar , electrode , optoelectronics , p–n junction , current density , optics , layer (electronics) , nanotechnology , chemistry , structural engineering , quantum mechanics , engineering , physics
The photoelectrochemical (PEC) activity of microstructured electrodes remains low despite the highly enlarged surface area and enhanced light harvesting. To obtain a deeper understanding of the effect of 3D geometry on the PEC performance, well‐defined WO 3 /n‐Si and WO 3 /pn‐Si micropillar arrays are fabricated and subjected to a quantitative analysis of the relationship between the geometry of the micropillars (length, pitch) and their PEC activity. For WO 3 /n‐Si micropillars, it is found that the photocurrent increases for WO 3 /n‐Si pillars, but not in proportion to the increase in surface area that results from increased pillar length or reduced pillar pitch. Optical simulations show that a reduced pillar pitch results in areas of low light intensity due to a shadowing effect. For WO 3 /pn‐Si micropillar photoelectrodes, the p–n junction enhances the photocurrent density up to a factor of 4 at low applied bias potential (0.8 V vs RHE) compared to the WO 3 /n‐Si. However, the enhancement in photocurrent density increases first and then decreases with reduced pillar pitch, which scales with the photovoltage generated by the p–n junction. This is related to an increased dead layer of the p–n junction Si surface, which results in a decreased photovoltage even though the total surface area increases.