High Aspect Ratio Silicon Wire Array Photoelectrochemical Cells

Maiolo, James R.; Kayes, Brendan M.; Filler, Michael A.; Putnam, Morgan C.; Kelzenberg, Michael D.; Atwater, Harry A.; Lewis, Nathan S.

doi:10.1021/ja074897c

Cited by 236 publications

(182 citation statements)

References 19 publications

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“…The p-Si wire arrays (SI Text) were formed into electrodes as described previously (13)(14)(15). Some wire-array samples were instead thermally oxidized at 1,100°C under O 2 (4,000 sccm) for 90 min, followed by electron-beam evaporation of >500 nm Al 2 O 3 (99.99%, Kurt Lesker) over the entire sample, and then by deposition of 200 nm of Ag.…”

Section: Experimental Methodsmentioning

confidence: 99%

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Evaluation and optimization of mass transport of redox species in silicon microwire-array photoelectrodes

Xiang

Meng

Lewis

2012

Proc. Natl. Acad. Sci. U.S.A.

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Physical integration of a Ag electrical contact internally into a metal/substrate/microstructured Si wire array/oxide/Ag/electrolyte photoelectrochemical solar cell has produced structures that display relatively low ohmic resistance losses, as well as highly efficient mass transport of redox species in the absence of forced convection. Even with front-side illumination, such wire-array based photoelectrochemical solar cells do not require a transparent conducting oxide top contact. In contact with a test electrolyte that contained 50 mM/5.0 mM of the cobaltocenium þ∕0 redox species in CH 3 CN-1.0 M LiClO 4 , when the counterelectrode was placed in the solution and separated from the photoelectrode, mass transport restrictions of redox species in the internal volume of the Si wire array photoelectrode produced low fill factors and limited the obtainable current densities to 17.6 mA cm −2 even under high illumination. In contrast, when the physically integrated internal Ag film served as the counter electrode, the redox couple species were regenerated inside the internal volume of the photoelectrode, especially in regions where depletion of the redox species due to mass transport limitations would have otherwise occurred. This behavior allowed the integrated assembly to operate as a twoterminal, stand-alone, photoelectrochemical solar cell. The current density vs. voltage behavior of the integrated photoelectrochemical solar cell produced short-circuit current densities in excess of 80 mA cm −2 at high light intensities, and resulted in relatively low losses due to concentration overpotentials at 1 Sun illumination. The integrated wire array-based device architecture also provides design guidance for tandem photoelectrochemical cells for solardriven water splitting.semiconductor/liquid junctions | Si microwire arrays | COMSOL Multiphysics T o yield optimal solar energy-conversion efficiencies, photoelectrochemical cells require highly effective mass transport of redox species between the photoelectrode and the counter electrode, as well as in the internal void volume of porous, microstructured photoelectrodes. Although the fundamental energyconversion properties of many semiconductor photoelectrodes are well-documented, the mass transport of reactants and products in highly structured electrochemical systems has received relatively little attention. Diffusion-limited mass transport during the electrochemical deposition of metals onto planar electrodes has been investigated by Scharifker and Hills (1) in the early 1980s, and has been further expanded upon in other studies (2-5). Penner et al. (6) have studied the mass-transport properties of conical and hemispherical ultramicroelectrodes in electrochemical cells. Mass transport in nanocrystalline TiO 2 -based dyesensitized solar cells has also been treated theoretically (7-12). Of specific interest herein is the mass transport of redox species in the internal pore volume of highly microstructured electrodes, such as Si wire array photoelectrodes.High aspect-ratio ...

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Section: Experimental Methodsmentioning

confidence: 99%

“…High aspect-ratio semiconductor microwire and nanowire array structures have shown promise in liquid junction devices for solar energy-conversion applications (13)(14)(15)(16)(17)(18). A key attribute of these wire array structures is the orthogonalization of the directions of light absorption and photogenerated charge-carrier collection (19).…”

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confidence: 99%

Evaluation and optimization of mass transport of redox species in silicon microwire-array photoelectrodes

Xiang

Meng

Lewis

2012

Proc. Natl. Acad. Sci. U.S.A.

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“…Absorbers that are structured in three dimensions, such as Si microwire arrays [14][15][16][17] provide an alternative, general approach to ameliorating the negative correlation between the ff and J ph . In such systems, a relatively high loading of catalyst can be positioned at the base of a high-aspect-ratio microwire array, leaving exposed a large proportion of the array (Fig.…”

Section: Introductionmentioning

confidence: 99%

Functional integration of Ni–Mo electrocatalysts with Si microwire array photocathodes to simultaneously achieve high fill factors and light-limited photocurrent densities for solar-driven hydrogen evolution

Shaner

McKone

Gray

et al. 2015

Energy Environ. Sci.

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An n + p-Si microwire array coupled with a two-layer catalyst film consisting of Ni-Mo nanopowder and TiO 2 light-scattering nanoparticles has been used to simultaneously achieve high fill factors and lightlimited photocurrent densities from photocathodes that produce H 2 (g) directly from sunlight and water.The TiO 2 layer scattered light back into the Si microwire array, while optically obscuring the underlying Ni-Mo catalyst film. In turn, the Ni-Mo film had a mass loading sufficient to produce high catalytic activity, on a geometric area basis, for the hydrogen-evolution reaction. The best-performing microwire array devices prepared in this work exhibited short-circuit photocurrent densities of À14.3 mA cm À2 , photovoltages of 420 mV, and a fill factor of 0.48 under 1 Sun of simulated solar illumination, whereas the equivalent planar Ni-Mo-coated Si device, without TiO 2 scatterers, exhibited negligible photocurrent due to complete light blocking by the Ni-Mo catalyst layer. Broader contextSolar-driven photoelectrochemical water splitting is a promising approach to enable the large-scale conversion and storage of solar energy. Few integrated systems have been realized that use earth-abundant semiconductor and catalyst materials for the half-reactions involved in solar-driven water-splitting, i.e. hydrogen evolution and oxygen evolution, while also achieving high energy-conversion efficiencies. We describe herein a hydrogen-evolving Si-based photoelectrode that exhibits high light-limited photocurrent densities, as well as high catalytic activities, while using a high mass loading of an earth-abundant electrocatalyst. The design is reminiscent of a membrane-electrode assembly as used for stand-alone fuel cell and electrolysis systems. The approach exploits the high aspect ratio of the absorber layer to avoid parasitic optical absorption normally associated with a thick catalyst layer on the surface of an illuminated photocathode.

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“…Several calculations and experimental results indicate that the ratio EQE/IQE can be nearly 1 for nanowire or nanocone arrays. 9,18,19 This is far to be the case for single nanowires. Several factors affect the absorption in a nanowire positioned on a substrate ( Fig.…”

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Fundamental limits in the external quantum efficiency of single nanowire solar cells

Heiß

Morral

2011

Applied Physics Letters

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The fundamental limits for the measurement of the efficiency of single nanowire solar cell devices are presented. We evaluate the effect of the substrate, light polarization, and existence of Mie resonances in the absorption of the solar spectrum for nanowires with diameters from 10 to 300 nm. We find that the efficiency measured under such configuration can be underestimated between a factor 1.6 and 7.0 for GaAs nanowires and between 6.7 and 15.9 for silicon nanowires. These results constitute a reference for understanding the limits in the measurement of single nanowire devices.

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High Aspect Ratio Silicon Wire Array Photoelectrochemical Cells

Cited by 236 publications

References 19 publications

Evaluation and optimization of mass transport of redox species in silicon microwire-array photoelectrodes

Evaluation and optimization of mass transport of redox species in silicon microwire-array photoelectrodes

Functional integration of Ni–Mo electrocatalysts with Si microwire array photocathodes to simultaneously achieve high fill factors and light-limited photocurrent densities for solar-driven hydrogen evolution

Fundamental limits in the external quantum efficiency of single nanowire solar cells

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