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Title: Investigation of Cd1-XMgxTe Alloys for Tandem Solar Cell Applications: Preprint

Abstract

Theoretical modeling of two-junction tandem solar cells shows that for optimal device performance, the bandgap of the top cell should be in the range of 1.6 to 1.8 eV. Cd1-xMgxTe (CMT) alloys have a lattice constant close to that of CdTe, and the addition of a small amount of Mg changes the bandgap considerably. In this paper, we present our work on developing CMT for solar cell applications. CMT films were prepared by vacuum deposition with co-evaporation of CdTe and Mg on substrates heated to 300-400 C. Films with a composition in the range of x = 0 to 0.66 were fabricated, and optical analysis of the films showed that the bandgap of the samples ranged from 1.5 to 2.3 eV and varied linearly with composition. For the fabrication of devices using these alloy films, we also investigated the effect of post-deposition CdCl2 heat treatment. We have investigated junctions between CdS and CMT alloys in the bandgap range of 1.5 to 1.8 eV for tandem cell applications. We have also worked on the ohmic contacts to the CMT alloy films using Cu/Au bilayers, and the preliminary data shows a significant effect of the contact processing on the device performance.

Authors:
; ; ; ; ; ;
Publication Date:
Research Org.:
National Renewable Energy Lab. (NREL), Golden, CO (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
891547
Report Number(s):
NREL/CP-520-39899
TRN: US200622%%89
DOE Contract Number:
AC36-99-GO10337
Resource Type:
Conference
Resource Relation:
Conference: Presented at the 2006 IEEE 4th World Conference on Photovoltaic Energy Conversion (WCPEC-4), 7-12 May 2006, Waikoloa, Hawaii
Country of Publication:
United States
Language:
English
Subject:
14 SOLAR ENERGY; 36 MATERIALS SCIENCE; ALLOYS; DEPOSITION; ENERGY CONVERSION; FABRICATION; HEAT TREATMENTS; PERFORMANCE; PROCESSING; SIMULATION; SOLAR CELLS; SUBSTRATES; TWO-JUNCTION TANDEM; SOLAR CELLS APPLICATION; DEVICE; BANDGAP; POLYCRYSTALLINE; Solar Energy - Photovoltaics

Citation Formats

Dhere, R., Ramanathan, K., Scharf, J., Moutinho, H., To, B., Duda, A., and Noufi, R. Investigation of Cd1-XMgxTe Alloys for Tandem Solar Cell Applications: Preprint. United States: N. p., 2006. Web. doi:10.1109/WCPEC.2006.279513.
Dhere, R., Ramanathan, K., Scharf, J., Moutinho, H., To, B., Duda, A., & Noufi, R. Investigation of Cd1-XMgxTe Alloys for Tandem Solar Cell Applications: Preprint. United States. doi:10.1109/WCPEC.2006.279513.
Dhere, R., Ramanathan, K., Scharf, J., Moutinho, H., To, B., Duda, A., and Noufi, R. Mon . "Investigation of Cd1-XMgxTe Alloys for Tandem Solar Cell Applications: Preprint". United States. doi:10.1109/WCPEC.2006.279513. https://www.osti.gov/servlets/purl/891547.
@article{osti_891547,
title = {Investigation of Cd1-XMgxTe Alloys for Tandem Solar Cell Applications: Preprint},
author = {Dhere, R. and Ramanathan, K. and Scharf, J. and Moutinho, H. and To, B. and Duda, A. and Noufi, R.},
abstractNote = {Theoretical modeling of two-junction tandem solar cells shows that for optimal device performance, the bandgap of the top cell should be in the range of 1.6 to 1.8 eV. Cd1-xMgxTe (CMT) alloys have a lattice constant close to that of CdTe, and the addition of a small amount of Mg changes the bandgap considerably. In this paper, we present our work on developing CMT for solar cell applications. CMT films were prepared by vacuum deposition with co-evaporation of CdTe and Mg on substrates heated to 300-400 C. Films with a composition in the range of x = 0 to 0.66 were fabricated, and optical analysis of the films showed that the bandgap of the samples ranged from 1.5 to 2.3 eV and varied linearly with composition. For the fabrication of devices using these alloy films, we also investigated the effect of post-deposition CdCl2 heat treatment. We have investigated junctions between CdS and CMT alloys in the bandgap range of 1.5 to 1.8 eV for tandem cell applications. We have also worked on the ohmic contacts to the CMT alloy films using Cu/Au bilayers, and the preliminary data shows a significant effect of the contact processing on the device performance.},
doi = {10.1109/WCPEC.2006.279513},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Mon May 01 00:00:00 EDT 2006},
month = {Mon May 01 00:00:00 EDT 2006}
}

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  • Fabrication and characterization of Cd{sub 1-x}Mg{sub x}Te(CMT) alloys and to determine their potential for device applications. Main emphasis is on the development of the devices in 1.5 to 1.8 eV range for the top cell of two-junction tandem solar cells. The conclusions are: (1) CMT alloy films with a wide composition range were fabricated; (2) the optical band gap shows a systematic variation with composition and CMT alloy films withstood the commonly used device processing steps for CdTe; and (3) they have fabricated cells with 5% efficiency in the energy gap range of 1.5 to 1.7 eV and established themore » viability of CMT for device applications.« less
  • Theoretical modeling of two-junction tandem solar cells shows that for optimal device performance, the bandgap of the top cell should be in the range of 1.6 to 1.8 eV. Cd{sub 1-x}Mg{sub x}Te (CMT) alloys have a lattice constant close to that of CdTe, and the addition of a small amount of Mg changes the bandgap considerably. In this paper, we present our work on developing CMT for solar cell applications. CMT films were prepared by vacuum deposition with co-evaporation of CdTe and Mg on substrates heated to 300-400 C. Films with a composition in the range of x=0 to 0.66more » were fabricated, and optical analysis of the films showed that the bandgap of the samples ranged from 1.5 to 2.3 eV and varied linearly with composition. For the fabrication of devices using these alloy films, we also investigated the effect of post-deposition CdCI2 heat treatment. We have investigated junctions between CdS and CMT alloys in the bandgap range of 1.5 to 1.8 eV for tandem cell applications. We have also worked on the ohmic contacts to the CMT alloy films using Cu/Au bilayers, and the preliminary data shows a significant effect of the contact processing on the device performance. We present the results on the materials properties of these alloys and the effect of post deposition treatments on the film properties and device performance for different alloy compositions and compare them to similar CdTe devices to determine their applicability in tandem solar cell applications.« less
  • Modeling of two-junction tandem devices shows that for optimal device performance, the bandgap of the top cell should be around 1.6-1.8 eV. CdZnTe alloys can be tailored to yield bandgaps in the desired range. In this study, we considered were used to fabricate these films, using close-spaced sublimation (CSS) and radio-frequency sputtering (RFS) techniques. In the first approach, we used mixed powders of CdTe and ZnTe as the source for film deposition by CSS. Even for the ZnTe/CdTe (95:5 ratio) source material, the deposited films were entirely CdTe due to higher vapor pressure of CdTe. In the second approach, wemore » used pre-alloyed CdZnTe powders (CERAC, Inc.) as the source. Due to the lower sticking coefficient of Zn, even for the source composition of 75% Zn, these films contained very low quantities of Zn (~5%). We tried unsuccessfully to increase the Zn content in the films by confining Zn vapor by enclosing the region between the source and substrate, reducing the substrate temperature to 400C, and adjusting the source/substance distance. Finally, we used thin-film couples consisting of 300-nm-thick CdTe deposited by CSS and 300-nm-thick ZnTe deposited by RFS; the samples were then heat-treated in cadmium chloride vapor. Compositional analysis of the samples showed extensive interdiffusion of Cd and Zn for the annealed samples. We will present the data on the various stack configurations of CdTe and ZnTe, the effect of different post-deposition anneals, the effect of oxygen on the interdiffusion and alloy formation and its possible correlation to the device performance degradation.« less
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