Photoreduction at illuminated p-type semiconducting silicon photoelectrodes. Evidence for Fermi level pinning

Journal Article · Wed May 21 00:00:00 EDT 1980 · J. Am. Chem. Soc.; (United States)

DOI:https://doi.org/10.1021/ja00531a003· OSTI ID:5112901

Bocarsly, A B; Bookbinder, D C; Dominey, R N; Lewis, N S; Wrighton, M S

Studies of p- and n-type Si electrodes are reported which show that semiconducting Si electrode surfaces do not allow efficient H/sub 2/ evolution in the dark (n type) or upon illumination with band gap or greater energy light (p type). The key experiment is that N,N'-dimethyl-4,4'-bipyridinium (PQ/sup 2 +/) is reversibly reduced at n-type Si in aqueous media at a pH where H/sub 2/ should be evolved at nearly the same potential, but no H/sub 2/ evolution current is observable. The PQ/sup 2+/+/.system may be useful as an electron-transfer mediator, since PQ/sup +/.can be used to effect generation of H/sub 2/ from H/sub 2/O using a heterogeneous catalyst. The PQ/sup +/.can be produced in an uphill sense by illumination of p-type Si in aqueous solutions. Studies of p-type Si in nonaqueous solvents show that PQ/sup 2 +/, PQ/sup +/., Ru(bpy)/sub 3//sup 2 +/, Ru(bpy)/sub 3//sup +/, and Ru(bpy)/sub 3//sup 0/ are all reducible upon illumination of the p-type Si. Interestingly, each species can be photoreduced at a potential approx. 500 mV more positive than at a reversible electrode in the dark. This result reveals that a p-type Si-based photoelectrochemical cell based on PQ/sup 2+/+/., PQ/sup +/l/sup 0//, Ru(bpy)/sub 3//sup 2+/+/, Ru(bpy)/sub 3//sup +/0/, or Ru(bpy)/sub 3//sup 0/-/ would all yield a common output photovoltage, despite the fact that the formal potentials for these couples vary by more than the band gap (1.1 V) of the photocathode. These data support the notion that p-type Si exhibits Fermi level pinning under the conditions employed.Surface chemistry is shown to be able to effect changes in interface kinetics for electrodes exhibiting Fermi level pinning.

• Research Organization: Massachusetts Inst. of Tech., Cambridge
• OSTI ID: 5112901
• Journal Information: J. Am. Chem. Soc.; (United States), Journal Name: J. Am. Chem. Soc.; (United States) Vol. 102:11; ISSN JACSA
• Country of Publication: United States
• Language: English

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ANODES
AQUEOUS SOLUTIONS
AZINES
BIPYRIDINES
CHEMICAL PREPARATION
CHEMICAL REACTIONS
CHEMISTRY
COMPLEXES
CONVERSION
DATA
DISPERSIONS
ELECTROCHEMICAL CELLS
ELECTROCHEMISTRY
ELECTRODES
ELECTROLYTIC CELLS
ELEMENTS
ENERGY CONVERSION
ENERGY LEVELS
EQUIPMENT
EXPERIMENTAL DATA
FERMI LEVEL
HETEROCYCLIC COMPOUNDS
HYDROGEN PRODUCTION
INFORMATION
MATERIALS
MIXTURES
NUMERICAL DATA
ORGANIC COMPOUNDS
ORGANIC NITROGEN COMPOUNDS
ORGANOMETALLIC COMPOUNDS
P-TYPE CONDUCTORS
PERFORMANCE
PHOTOANODES
PHOTOELECTROCHEMICAL CELLS
PHOTOELECTROLYTIC CELLS
PYRIDINES
REDUCTION
RUTHENIUM COMPLEXES
SEMICONDUCTOR MATERIALS
SEMIMETALS
SILICON
SOLAR ENERGY CONVERSION
SOLAR EQUIPMENT
SOLUTIONS
SYNTHESIS
TRANSITION ELEMENT COMPLEXES
VOLTAMETRY