High-performance Si microwire photovoltaics

Kelzenberg, Michael D.; Turner-Evans, Daniel B.; Putnam, Morgan C.; Boettcher, Shannon W.; Briggs, Ryan M.; Baek, Jae Yeon; Lewis, Nathan S.; Atwater, Harry A.

doi:10.1039/c0ee00549e

Cited by 196 publications

(184 citation statements)

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“…This discrepancy between the simulations and the observations can likely be attributed to a non-uniform current density distribution along the length of the microwire array, as well as to the long minority-carrier diffusion length of the p-Si microwire arrays. A long minority-carrier diffusion length (>30 μm), as has been observed in similar p-Si microwire arrays (26,27), will allow lateral mobility of the photogenerated charge carriers along the wire length, and thus will relax the mass transport limitations relative to those indicated by simulations, which assumed a constant flux of photogenerated charge carriers along the length of the wires in the array.…”

Section: Discussionmentioning

confidence: 97%

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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: Discussionmentioning

confidence: 97%

“…The observed J sc can be further improved by light trapping techniques (25)(26)(27)(28). Using an antireflective coating, a Ag back-reflector and embedded light-scatterers, these wire-array substrates have exhibited up to 96% peak absorption and have been shown to absorb up to 85% of day-integrated, above-bandgap direct-beam sunlight (25).…”

Section: Discussionmentioning

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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“…These samples were then spun at 1000 RPM for 30 s and cured at 150 °C for 30 min to produce a 10-20 μm thick PDMS layer selectively at the base of the wire array. 6 After a ~ 2 s etch in a 1:1 mixture of 1.0 M tetrabutylammonium fluoride in tetrahydrofuran (SigmaAldrich) and dimethylformamide (referred to as 'PDMS etch') and a H 2 O rinse, these partially in-filled arrays were immersed for 5 min in BHF to remove the exposed diffusion-barrier oxide.…”

Section: S2mentioning

confidence: 99%

Photoelectrochemical Hydrogen Evolution Using Si Microwire Arrays

et al. 2011

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Figure S1. Panel (a) shows the J-E data collected for the electrode fabricated with 'enhanced' absorption due to light-trapping elements, in 0.5 M aq. H 2 SO 4 under ELH-type W-halogen solar simulation. Panel (b) shows a cross-sectional SEM image of the same sample. Panel (c) compares the spectral response collected for the sample with light-trapping elements ('enhanced') versus the spectral response for the normal sample. The red response in the 'enhanced' cell is significantly improved. Panel (d) shows the increased J sc with reduced angle dependence, for the enhanced sample compared to the normal sample. Panel (e) shows a digital photograph of a normal Pt/n + p-Si wire-array electrode evolving hydrogen under ~ 1 sun illumination. Small bubbles can be seen nucleating on the wire-array surface. The larger bubbles are stuck on the epoxy, and are the result of the coalescence of many small bubbles. S1

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“…[1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16] For example, the optical properties of arrays of nano-and microscale wires have been exploited for enhanced light absorption in photovoltaic devices, [16][17][18][19] however, the ability to substantially manipulate absorption in individual nanoscale structures has not been well established. In order to quantify optical resonances supported in individual NWs, scattering [20][21][22] and absorption cross-sections 5,6,11,[23][24][25][26] have been measured or calculated.…”

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confidence: 99%

“…6 By comparison, EQE values of ~0.15 have been reported for microscale devices based on Al-Si Schottky junctions 23 and values of ~1.1 for devices with coaxial p-n junctions that included a back-side reflector. 11 Several reports of relative EQE values have been reported for Si and Ge nanowire devices acting as photodetectors. 5,24,25 Our integrated approach to understanding the role of morphology on light absorption in individual p/i/n Si NWs is illustrated in Figure 1.…”

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confidence: 99%