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 a...

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Bibliographic Details
Published in:Energy & environmental science 2014-10, Vol.7 (10), p.3424-3430
Main Authors: Pala, Ragip A, Leenheer, Andrew J, Lichterman, Michael, Atwater, Harry A, Lewis, Nathan S
Format: Article
Language:English
Subjects:
Aqueous electrolytes
Contact resistance
Diffusion length
Doping
ENGINEERING
Minority carriers
Photocurrent
Photoelectric effect
Semiconductors
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Summary: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.
ISSN:1754-5692
1754-5706
DOI:10.1039/c4ee01580k