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Title: Real Time Spectroscopic Ellipsometry Analysis of First Stage CuIn1−xGaxSe2 Growth: Indium-Gallium Selenide Co-Evaporation

Abstract

Real time spectroscopic ellipsometry (RTSE) has been applied for in-situ monitoring of the first stage of copper indium-gallium diselenide (CIGS) thin film deposition by the three-stage co-evaporation process used for fabrication of high efficiency thin film photovoltaic (PV) devices. The first stage entails the growth of indium-gallium selenide (In 1−xGax) 2Se 3 (IGS) on a substrate of Mo-coated soda lime glass maintained at a temperature of 400 °C. This is a critical stage of CIGS deposition because a large fraction of the final film thickness is deposited, and as a result precise compositional control is desired in order to achieve the optimum performance of the resulting CIGS solar cell. RTSE is sensitive to monolayer level film growth processes and can provide accurate measurements of bulk and surface roughness layer thicknesses. These in turn enable accurate measurements of the bulk layer optical response in the form of the complex dielectric function ε = ε 1 − iε 2, spectra. Here, RTSE has been used to obtain the (ε 1, ε 2) spectra at the measurement temperature of 400 °C for IGS thin films of different Ga contents (x) deduced from different ranges of accumulated bulk layer thickness during the deposition process.more » Applying an analytical expression in common for each of the (ε 1, ε 2) spectra of these IGS films, oscillator parameters have been obtained in the best fits and these parameters in turn have been fitted with polynomials in x. From the resulting database of polynomial coefficients, the (ε 1, ε 2) spectra can be generated for any composition of IGS from the single parameter, x. The results have served as an RTSE fingerprint for IGS composition and have provided further structural information beyond simply thicknesses, for example information related to film density and grain size. The deduced IGS structural evolution and the (ε 1, ε 2) spectra have been interpreted as well in relation to observations from scanning electron microscopy, X-ray diffractometry and energy-dispersive X-ray spectroscopy profiling analyses. Overall the structural, optical and compositional analysis possible by RTSE has assisted in understanding the growth and properties of three stage CIGS absorbers for solar cells and shows future promise for enhancing cell performance through monitoring and control.« less

Authors:
 [1];  [1];  [1];  [1];  [1];  [1];  [1];  [1];  [1];  [1];  [2];  [1];  [1]
  1. Univ. of Toledo, OH (United States). Wright Center for Photovoltaics Innovation and Commercialization (PVIC) and Dept. of Physics and Astronomy
  2. Old Dominion Univ., Norfolk, VA (United States). Virginia Inst. of Photovoltaics
Publication Date:
Research Org.:
Old Dominion Univ., Norfolk, VA (United States)
Sponsoring Org.:
USDOE Office of Energy Efficiency and Renewable Energy (EERE)
OSTI Identifier:
1510466
Grant/Contract Number:  
EE0005400
Resource Type:
Accepted Manuscript
Journal Name:
Materials
Additional Journal Information:
Journal Volume: 11; Journal Issue: 1; Journal ID: ISSN 1996-1944
Publisher:
MDPI
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; spectroscopic ellipsometry; III2-VI3 semiconductor materials; real time analysis; complex dielectric function; photovoltaic cells; thicknessmeasurement; compositional analysis; CuIn1􀀀xGaxSe2

Citation Formats

Pradhan, Puja, Aryal, Puruswottam, Attygalle, Dinesh, Ibdah, Abdel-Rahman, Koirala, Prakash, Li, Jian, Bhandari, Khagendra, Liyanage, Geethika, Ellingson, Randy, Heben, Michael, Marsillac, Sylvain, Collins, Robert, and Podraza, Nikolas. Real Time Spectroscopic Ellipsometry Analysis of First Stage CuIn1−xGaxSe2 Growth: Indium-Gallium Selenide Co-Evaporation. United States: N. p., 2018. Web. doi:10.3390/ma11010145.
Pradhan, Puja, Aryal, Puruswottam, Attygalle, Dinesh, Ibdah, Abdel-Rahman, Koirala, Prakash, Li, Jian, Bhandari, Khagendra, Liyanage, Geethika, Ellingson, Randy, Heben, Michael, Marsillac, Sylvain, Collins, Robert, & Podraza, Nikolas. Real Time Spectroscopic Ellipsometry Analysis of First Stage CuIn1−xGaxSe2 Growth: Indium-Gallium Selenide Co-Evaporation. United States. doi:10.3390/ma11010145.
Pradhan, Puja, Aryal, Puruswottam, Attygalle, Dinesh, Ibdah, Abdel-Rahman, Koirala, Prakash, Li, Jian, Bhandari, Khagendra, Liyanage, Geethika, Ellingson, Randy, Heben, Michael, Marsillac, Sylvain, Collins, Robert, and Podraza, Nikolas. Tue . "Real Time Spectroscopic Ellipsometry Analysis of First Stage CuIn1−xGaxSe2 Growth: Indium-Gallium Selenide Co-Evaporation". United States. doi:10.3390/ma11010145. https://www.osti.gov/servlets/purl/1510466.
@article{osti_1510466,
title = {Real Time Spectroscopic Ellipsometry Analysis of First Stage CuIn1−xGaxSe2 Growth: Indium-Gallium Selenide Co-Evaporation},
author = {Pradhan, Puja and Aryal, Puruswottam and Attygalle, Dinesh and Ibdah, Abdel-Rahman and Koirala, Prakash and Li, Jian and Bhandari, Khagendra and Liyanage, Geethika and Ellingson, Randy and Heben, Michael and Marsillac, Sylvain and Collins, Robert and Podraza, Nikolas},
abstractNote = {Real time spectroscopic ellipsometry (RTSE) has been applied for in-situ monitoring of the first stage of copper indium-gallium diselenide (CIGS) thin film deposition by the three-stage co-evaporation process used for fabrication of high efficiency thin film photovoltaic (PV) devices. The first stage entails the growth of indium-gallium selenide (In1−xGax)2Se3 (IGS) on a substrate of Mo-coated soda lime glass maintained at a temperature of 400 °C. This is a critical stage of CIGS deposition because a large fraction of the final film thickness is deposited, and as a result precise compositional control is desired in order to achieve the optimum performance of the resulting CIGS solar cell. RTSE is sensitive to monolayer level film growth processes and can provide accurate measurements of bulk and surface roughness layer thicknesses. These in turn enable accurate measurements of the bulk layer optical response in the form of the complex dielectric function ε = ε1 − iε2, spectra. Here, RTSE has been used to obtain the (ε1, ε2) spectra at the measurement temperature of 400 °C for IGS thin films of different Ga contents (x) deduced from different ranges of accumulated bulk layer thickness during the deposition process. Applying an analytical expression in common for each of the (ε1, ε2) spectra of these IGS films, oscillator parameters have been obtained in the best fits and these parameters in turn have been fitted with polynomials in x. From the resulting database of polynomial coefficients, the (ε1, ε2) spectra can be generated for any composition of IGS from the single parameter, x. The results have served as an RTSE fingerprint for IGS composition and have provided further structural information beyond simply thicknesses, for example information related to film density and grain size. The deduced IGS structural evolution and the (ε1, ε2) spectra have been interpreted as well in relation to observations from scanning electron microscopy, X-ray diffractometry and energy-dispersive X-ray spectroscopy profiling analyses. Overall the structural, optical and compositional analysis possible by RTSE has assisted in understanding the growth and properties of three stage CIGS absorbers for solar cells and shows future promise for enhancing cell performance through monitoring and control.},
doi = {10.3390/ma11010145},
journal = {Materials},
number = 1,
volume = 11,
place = {United States},
year = {2018},
month = {1}
}

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