Photoelectrochemical Behavior of n-type Si(100) Electrodes Coated with Thin Films of Manganese Oxide Grown by Atomic Layer Deposition
By Strandwitz, Nicholas C.; Comstock, David J.; Grimm, Ronald L.; Nichols-Nielander, Adam C.; Elam, Jeffrey & Lewis, Nathan S.
Published in The Journal of Physical Chemistry C
2013
Abstract
Thin (10 nm) films of manganese oxide have been deposited by atomic layer deposition (ALD) onto n-type silicon and onto degenerately doped p-type silicon. The photoelectrochemical properties of the resulting semiconductor/metal-oxide structures were evaluated in contact with aqueous 0.35 M K4Fe(CN)6 -0.05 M K3Fe(CN)6, 1.0 M KOH(aq), as well as in contact with a series of nonaqueous one-electron, reversible, outer-sphere redox systems. Under simulated air mass (AM) 1.5 illumination in contact with 0.35 M K4Fe(CN)6 -0.05 M K3Fe(CN)6(aq), MnO-coated n-Si photoanodes displayed open-circuit voltages of up to 550 mV and stable anodic currents for periods of hours at 0.0 V versus the solution potential. In contact with 1.0 M KOH(aq), at current densities of ∼25 mA cm -2, MnO|Si photoanodes under 100 mW cm -2 of simulated AM 1.5 illumination yielded stable oxygen evolution for 10 -30 min. Variation in the thickness of the MnO films from 4 to 20 nm indicated the presence of a series resistance in the MnO film that limited the fill factor and thus the solar energy-conversion efficiency of the photoelectrodes. Open-circuit photovoltages of 30 and 450 mV, respectively, were observed in contact with cobaltocene+/0 or ferrocene+/0 in CH3CN, indicating that the energetics of the MnO-coated Si surfaces were a function of the electrochemical potential of the contacting electrolyte solution.