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Title: The effects of CdCl sub 2 on the electronic properties of molecular-beam epitaxially grown CdTe/CdS heterojunction solar cells

Abstract

Significant improvements in CdTe/CdS solar cell efficiency are commonly observed as a result of a postdeposition CdCl{sub 2} dip followed by a 400 {degree}C heat treatment during cell processing which increases CdTe grain size. In this paper, we investigate the electronic mechanisms responsible for CdCl{sub 2}-induced improvement in cell performance along with possible performance-limiting defects resulting from this process in molecular-beam epitaxy-grown polycrystalline CdTe/CdS solar cells. Current density-voltage-temperature ({ital J}-{ital V}-{ital T}) analysis revealed that the CdCl{sub 2} treatment changes the dominant current transport mechanism from interface recombination/tunneling to depletion region recombination, suggesting a decrease in the density and dominance of interface states due to the CdCl{sub 2} treatment. It is shown that the change in transport mechanism is associated with (a) an increase in heterojunction barrier height from 0.56 to 0.85 eV, (b) a decrease in dark leakage current from 4.7{times}10{sup {minus}7} A/cm{sup 2} to 2.6{times}10{sup {minus}9} A/cm{sup 2} and, (c) an increase in cell {ital V}{sub oc} from 385 to 720 mV. The CdCl{sub 2} also improved the optical response of the cell. Substantial increases in the surface photovoltage and quantum efficiency accompanied by a decrease in the bias dependence of the spectral response in the CdCl{sub 2}-treatedmore » structures indicate that the CdCl{sub 2} treatment improves carrier collection from the bulk as well as across the heterointerface. However, deep level transient spectroscopy measurements detected a hole trap within the CdTe depletion region of the CdCl{sub 2}-treated devices at {ital E}{sub {ital v}} + 0.64 eV which is attributed to the formation of {ital V}{sub Cd}-related defects during the annealing process after the CdCl{sub 2} dip.« less

Authors:
; ; ;  [1]
  1. School of Electrical Engineering and Microelectronics Research Center, Georgia Institute of Technology, Atlanta, Georgia 30332 (US)
Publication Date:
OSTI Identifier:
5668820
Resource Type:
Journal Article
Journal Name:
Journal of Applied Physics; (USA)
Additional Journal Information:
Journal Volume: 70:2; Journal ID: ISSN 0021-8979
Country of Publication:
United States
Language:
English
Subject:
14 SOLAR ENERGY; CADMIUM SULFIDE SOLAR CELLS; EFFICIENCY; FABRICATION; CADMIUM TELLURIDE SOLAR CELLS; CADMIUM CHLORIDES; CADMIUM SULFIDES; CADMIUM TELLURIDES; HETEROJUNCTIONS; MOLECULAR BEAM EPITAXY; PERFORMANCE; CADMIUM COMPOUNDS; CADMIUM HALIDES; CHALCOGENIDES; CHLORIDES; CHLORINE COMPOUNDS; DIRECT ENERGY CONVERTERS; EPITAXY; EQUIPMENT; HALIDES; HALOGEN COMPOUNDS; INORGANIC PHOSPHORS; JUNCTIONS; PHOSPHORS; PHOTOELECTRIC CELLS; PHOTOVOLTAIC CELLS; SEMICONDUCTOR JUNCTIONS; SOLAR CELLS; SOLAR EQUIPMENT; SULFIDES; SULFUR COMPOUNDS; TELLURIDES; TELLURIUM COMPOUNDS; 140501* - Solar Energy Conversion- Photovoltaic Conversion

Citation Formats

Ringel, S A, Smith, A W, MacDougal, M H, and Rohatgi, A. The effects of CdCl sub 2 on the electronic properties of molecular-beam epitaxially grown CdTe/CdS heterojunction solar cells. United States: N. p., 1991. Web. doi:10.1063/1.349652.
Ringel, S A, Smith, A W, MacDougal, M H, & Rohatgi, A. The effects of CdCl sub 2 on the electronic properties of molecular-beam epitaxially grown CdTe/CdS heterojunction solar cells. United States. doi:10.1063/1.349652.
Ringel, S A, Smith, A W, MacDougal, M H, and Rohatgi, A. Mon . "The effects of CdCl sub 2 on the electronic properties of molecular-beam epitaxially grown CdTe/CdS heterojunction solar cells". United States. doi:10.1063/1.349652.
@article{osti_5668820,
title = {The effects of CdCl sub 2 on the electronic properties of molecular-beam epitaxially grown CdTe/CdS heterojunction solar cells},
author = {Ringel, S A and Smith, A W and MacDougal, M H and Rohatgi, A},
abstractNote = {Significant improvements in CdTe/CdS solar cell efficiency are commonly observed as a result of a postdeposition CdCl{sub 2} dip followed by a 400 {degree}C heat treatment during cell processing which increases CdTe grain size. In this paper, we investigate the electronic mechanisms responsible for CdCl{sub 2}-induced improvement in cell performance along with possible performance-limiting defects resulting from this process in molecular-beam epitaxy-grown polycrystalline CdTe/CdS solar cells. Current density-voltage-temperature ({ital J}-{ital V}-{ital T}) analysis revealed that the CdCl{sub 2} treatment changes the dominant current transport mechanism from interface recombination/tunneling to depletion region recombination, suggesting a decrease in the density and dominance of interface states due to the CdCl{sub 2} treatment. It is shown that the change in transport mechanism is associated with (a) an increase in heterojunction barrier height from 0.56 to 0.85 eV, (b) a decrease in dark leakage current from 4.7{times}10{sup {minus}7} A/cm{sup 2} to 2.6{times}10{sup {minus}9} A/cm{sup 2} and, (c) an increase in cell {ital V}{sub oc} from 385 to 720 mV. The CdCl{sub 2} also improved the optical response of the cell. Substantial increases in the surface photovoltage and quantum efficiency accompanied by a decrease in the bias dependence of the spectral response in the CdCl{sub 2}-treated structures indicate that the CdCl{sub 2} treatment improves carrier collection from the bulk as well as across the heterointerface. However, deep level transient spectroscopy measurements detected a hole trap within the CdTe depletion region of the CdCl{sub 2}-treated devices at {ital E}{sub {ital v}} + 0.64 eV which is attributed to the formation of {ital V}{sub Cd}-related defects during the annealing process after the CdCl{sub 2} dip.},
doi = {10.1063/1.349652},
journal = {Journal of Applied Physics; (USA)},
issn = {0021-8979},
number = ,
volume = 70:2,
place = {United States},
year = {1991},
month = {7}
}