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Research Papers

# Effect of Chemical Treatment on the Optical Properties of a Cadmium Telluride Photovoltaic Device Investigated by Spectroscopic Ellipsometry

[+] Author and Article Information
Sandeep Kohli

Department of Chemistry, Colorado State University, Fort Collins, CO 80523sandeep.kohli@colostate.edu

Venkatesan Manivannan

Department of Chemistry, Colorado State University, Fort Collins, CO 80523; Department of Mechanical Engineering, Materials Engineering Laboratory, Colorado State University, Fort Collins, CO 80523

James N. Hilfiker

J. A. Woollam Co., Inc., 645 Main Street, Suite 102, Lincoln, NE 68508

Patrick R. McCurdy

Department of Chemistry, Colorado State University, Fort Collins, CO 80523

Robert A. Enzenroth, Kurt L. Barth, Westcott P. Smith, Richard Luebs, Walajabad S. Sampath

Department of Mechanical Engineering, Materials Engineering Laboratory, Colorado State University, Fort Collins, CO 80523

J. Sol. Energy Eng 131(2), 021009 (Apr 02, 2009) (7 pages) doi:10.1115/1.3097282 History: Received February 12, 2008; Revised November 07, 2008; Published April 02, 2009

## Abstract

Spectroscopic ellipsometry has been successfully used to characterize the CdS/CdTe heterojunction solar cell deposited on TEC15 glass. The effects of copper treatment on the optical properties of a cadmium chloride treated photovoltaic device were investigated using ellipsometry. No changes in either the band gaps or critical points of CdTe layer were noticed as a result of copper treatment. The copper treated CdTe layer exhibited a higher refractive index in the visible and longer wavelengths $(≤3 eV)$, as compared with the untreated layer. This was attributed to the increased disorder in the case of copper treated layer.

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Topics: Glass , Solar cells

## Figures

Figure 1

Flow chart of the SE measurements performed on various samples

Figure 2

(a) Experimental (∘) and modeled (——) spectroscopic ellipsometry parameters Psi for the TEC15 glass. Angles of incidence for measurements are also shown. (b) Graded refractive index “n” extinction coefficient “k” of the SnOx:F layer. Surface layer n (△) and k (▲); top layer n (X) and k (◼); bottom layer n (○) and k (●).

Figure 3

(a) Spectroscopic ellipsometry parameter Psi for the untreated CdS/CdTe heterojunction PV device deposited on TEC15 glass. (b) Experimental (•) and modeled (——) spectroscopic ellipsometry parameters Psi for the CdCl2 treated CdS/CdTe heterojunction PV device deposited on TEC15 glass. Angles of incidence for measurements are also shown. (c) Experimental (∘) and modeled (——) spectroscopic ellipsometry parameters Psi for the CuCl2 and CdCl2 treated CdS/CdTe heterojunction PV devices deposited on the TEC15 glass. Angles of incidence for measurements are also shown.

Figure 4

Cross-sectional SEM images of completed CdTe/CdS PV device: (bottom) with CdCl2 treatment and (top) with CdCl2 and Cu treatments

Figure 5

(a) Real (ε1) and (b) imaginary (ε2) components of the dielectric constant as a function of energy for CdTe. CdTe layer before (◻) and after (○) exposure to the vapor flux of copper compound. Optical constants for bulk CdTe layer from parametric layer fitted to Aspnes (14) data are also shown (△).

Figure 6

Tauc plots for CdTe layer (a) before and (b) after exposure to the copper compound vapor flux

Figure 7

Second order derivative of the real (ε1) and imaginary (ε2) components of the dielectric constant. CdTe layer before (◻) and after (○) exposure to the vapor flux of copper compound. Optical constants for bulk CdTe layer from parametric layer fitted to Aspnes (14) data are also shown (△).

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