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Published October 2014 | Supplemental Material + Published
Journal Article Open

Measurement of minority-carrier diffusion lengths using wedge-shaped semiconductor photoelectrodes


Measurement of the photocurrent as a function of the thickness of a light absorber has been shown herein both theoretically and experimentally to provide a method for determination of the minority-carrier diffusion length of a sample. To perform the measurement, an illuminated spot of photons with an energy well above the band gap of the material was scanned along the thickness gradient of a wedge-shaped, rear-illuminated semiconducting light absorber. Photogenerated majority carriers were collected through a back-side transparent ohmic contact, and a front-side liquid or Schottky junction collected the photogenerated minority carriers. Calculations showed that the diffusion length could be evaluated from the exponential variation in photocurrent as a function of the thickness of the sample. Good agreement was observed between experiment and theory for a solid-state silicon Schottky junction measured using this method. As an example for the application of the technique to semiconductor/liquid-junction photoelectrodes, the minority-carrier diffusion length was determined for graded thickness, sputtered tungsten trioxide and polished bismuth vanadate films under back-illumination in contact with an aqueous electrolyte. This wedge technique does not require knowledge of the spectral absorption coefficient, doping, or surface recombination velocity of the sample.

Additional Information

© Royal Society of Chemistry 2014. Received 22 May 2014, Accepted 29 July 2014. First published online 29 July 2014. This material is based upon work performed by the Joint Center for Artificial Photosynthesis, a DOE Energy Innovation Hub, supported through the Office of Science of the U.S. Department of Energy under Award Number DE-SC0004993. We thank C. Garland for advice on polishing techniques. Electronic supplementary information (ESI) available: Additional equations for photocurrent calculations, XRD for WO_3 deposited at various temperature, optical determination of thickness profile, cyclic voltammetry scan of WO_3 electrodes, and further details on the ALD processing and polishing. See DOI: 10.1039/c4ee01580k

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August 20, 2023
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