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Issue 10, 2014
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Measurement of minority-carrier diffusion lengths using wedge-shaped semiconductor photoelectrodes

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Abstract

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.

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

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Supplementary files

Article information


Submitted
22 May 2014
Accepted
29 Jul 2014
First published
29 Jul 2014

Energy Environ. Sci., 2014,7, 3424-3430
Article type
Paper
Author version available

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

R. A. Pala, A. J. Leenheer, M. Lichterman, H. A. Atwater and N. S. Lewis, Energy Environ. Sci., 2014, 7, 3424
DOI: 10.1039/C4EE01580K

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