Discussion of some "trap signatures" observed by admittance spectroscopy in CdTe thin-film solar cells

Jian V. Li, Steve W. Johnston, Xiaonan Li, David S. Albin, Timothy A. Gessert, Dean H. Levi

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27 Citations (Scopus)


Considerable ambiguity and controversy exist concerning the defect signatures (H1, H2, and H3) frequently observed in admittance spectroscopy of thin-film CdTe solar cells. We prove that the commonly labeled H1 defects, observed in all devices in this study, are actually due to the freeze-out of the majority carriers in the neutral CdTe absorber. This freeze-out is evident in the temperature dependencies of capacitance, carrier concentration, and depletion region width. Contrary to intuitive expectation, the activation energy of freeze-out is less than, not identical to, that of the conductivity. In some other cases, H2 or H3 are observed and attributed to the back-contact potential barrier, rather than to the carrier emission from the traps. We extract the back-contact barrier height from the activation energy of the saturation current determined from the temperature-dependent current-voltage curves using the back-to-back diode model. The back-contact barrier height agrees well with the H2 or H3 energy determined by admittance spectroscopy. We present a more comprehensive and realistic equivalent circuit that includes the admittances from both the back-contact and the neutral absorber.

Original languageEnglish
Article number064501
JournalJournal of Applied Physics
Issue number6
Publication statusPublished - 2010 Sep 15

All Science Journal Classification (ASJC) codes

  • Physics and Astronomy(all)


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