Welcome to the new version of CaltechAUTHORS. Login is currently restricted to library staff. If you notice any issues, please email coda@library.caltech.edu
Published January 20, 2011 | Supplemental Material
Journal Article Open

pH-Independent, 520 mV Open-Circuit Voltages of Si/Methyl Viologen^(2+/+) Contacts Through Use of Radial n^+p-Si Junction Microwire Array Photoelectrodes


The effects of introducing an n^+-doped emitter layer have been evaluated for both planar Si photoelectrodes and for radial junction Si microwire-array photoelectrodes. In contact with the pH-independent, one-electron, outer-sphere, methyl viologen redox system (denoted MV^(2+/+)), both planar and wire array p-Si photoelectrodes yielded open-circuit voltages, V_(oc), that varied with the pH of the solution. The highest V_(oc) values were obtained at pH = 2.9, with V_(oc) = 0.53 V for planar p-Si electrodes and V_(oc) = 0.42 V for vapor−liquid−solid catalyzed p-Si microwire array samples, under 60 mW cm^(−2) of 808 nm illumination. Increases in the pH of the electrolyte produced a decrease in V_(oc) by approximately −44 mV/pH unit for planar electrodes, with similar trends observed for the Si microwire array electrodes. In contrast, introduction of a highly doped, n^+ emitter layer produced V_(oc) = 0.56 V for planar Si electrodes and V_(oc) = 0.52 V for Si microwire array electrodes, with the photoelectrode properties in each system being essentially independent of pH over six pH units (3 < pH < 9). Hence, formation of an n^+ emitter layer not only produced nearly identical photovoltages for planar and Si microwire array photoelectrodes, but decoupled the band energetics of the semiconductor (and hence the obtainable photovoltage) from the value of the redox potential of the solution. The formation of radial junctions on Si microwire arrays thus provides an approach to obtaining Si-based photoelectrodes with high-photovoltages that can be used for a variety of photoelectrochemical processes, including potentially the hydrogen evolution reaction, under various pH conditions, regardless of the intrinsic barrier height and flat-band properties of the Si/liquid contact.

Additional Information

© 2010 American Chemical Society. Received September 24, 2010; Revised Manuscript Received: November 26, 2010, Published on Web 12/23/2010. We acknowledge the Stanford Global Climate and Energy Project and the U.S. Department of Energy (grant DE-FG02-05ER15754) for financial support. We acknowledge critical support and infrastructure provided for this work by the Kavli Nanoscience Institute at Caltech. S.W.B. thanks the Kavli Nanoscience Institute for a postdoctoral fellowship. M.G.W acknowledges support from an NSF American Competitiveness in Chemistry postdoctoral fellowship (CHE-0937048). D. Turner-Evans, J. Ku, and Dr. R. Grimm are thanked for their contributions.

Attached Files

Supplemental Material - jp109147p_si_001.pdf


Files (140.3 kB)
Name Size Download all
140.3 kB Preview Download

Additional details

August 19, 2023
October 23, 2023