Theoretical Analysis of Effects of Deep Level, Back Contact, and Absorber Thickness on Capacitance-Voltage Profiling of CdTe Thin-Film Solar Cells

Jian V. Li, Adam F. Halverson, Oleg V. Sulima, Shubhra Bansal, James M. Burst, Teresa M. Barnes, Timothy A. Gessert, Dean H. Levi

Research output: Contribution to journalArticlepeer-review

60 Scopus Citations

Abstract

The apparent carrier density profile measured by the capacitancevoltage technique in CdTe thin-film solar cells frequently displays a distinctive U-shape. We show that, even assuming a uniform carrier density, such a U-shape may arise from deep levels, a non-ohmic back-contact, and a thin absorber, which are commonly present in practical CdTe thin-film solar cells. A thin CdTe absorber contributes to the right branch of the U-shape due to a punch-through effect at reverse or zero biases, when the CdTe absorber is nearly fully depleted. A rectifying back-contact contributes to both branches of the U-shape due to voltage sharing with the front junction under a forward bias and early punch-through under a reverse bias. Deep levels contribute to the right branch, but also raise the bottom of the U-shape, leading to an overestimate of carrier density.

Original languageAmerican English
Pages (from-to)126-131
Number of pages6
JournalSolar Energy Materials and Solar Cells
Volume100
DOIs
StatePublished - May 2012

NREL Publication Number

  • NREL/JA-5200-53927

Keywords

  • Absorber thickness
  • Back contact
  • Capacitancevoltage
  • CdTe
  • Deep level

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