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Characterization of CdS/CdTe thin‐film solar cells by admittance spectroscopy and deep‐level transient spectroscopy

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1 Author(s)
Isett, L.C. ; Research Laboratories, Eastman Kodak Company, Rochester, New York 14650

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Admittance spectroscopy, deep‐level transient spectroscopy, and deep‐level optical spectroscopy were used to characterize CdS/CdTe thin‐film solar cells prepared by close‐spaced sublimation. These devices are n+/p‐type hetero‐ (or shallow homo‐) junctions, and deep levels in the p‐CdTe layer are observed. The energy levels within the band gap can be divided into three groups. The first group consists of the shallow (≪0.1 eV from the band edge) acceptors and donors, observed in electrical characterization only as the net carrier concentration. A band of midgap levels with activation energies of 0.6–0.8 eV in deep‐level transient spectroscopy is observed. The emission rates and activation energies for these levels agree with deep donor levels found in n‐type CdTe. A third band of levels is found with activation energies of 0.28–0.45 eV in admittance spectroscopy. These levels are seen in deep‐level optical spectroscopy and also in deep‐level transient spectroscopy, provided that a large forward‐bias pulse is used to fill the level. The emission rates in the third band agree with donor levels observed in n‐CdTe. Estimates of concentrations suggest that the concentration of the group two defects (midgap donors) is ∼0.8 of the net shallow acceptor concentration.

Published in:

Journal of Applied Physics  (Volume:56 ,  Issue: 12 )