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Title: Soft X-ray absorption spectroscopy investigation of the surface chemistry and treatments of copper indium gallium diselenide (CIGS)

Abstract

The surface and near surface structure of copper-indium-gallium-selenide (CIGS) absorber layers is integral to the producing a high-quality photovoltaic junction. By using X-ray absorption spectroscopy (XAS) and monitoring multiple elemental absorption edges with both theory and experiment, we are able to identify several features of the surface of CIGS as a function of composition and surface treatments. The XAS data shows trends in the near surface region of oxygen, copper, indium and gallium species as the copper content is varied in the films. The oxygen surface species are also monitored through a series of experiments that systematically investigates the effects of water and various solutions of: ammonium hydroxide, cadmium sulfate, and thiourea. These being components of cadmium sulfide chemical bath deposition (CBD). Characteristics of the CBD are correlated with a restorative effect that produces as normalized, uniform surface chemistry as measured by XAS. This surface chemistry is found in CIGS solar cells with excellent power conversion efficiency (<19%). The results provide new insight for CIGS processing strategies that seek to replace CBD and/or cadmium sulfide.

Authors:
; ; ; ; ; ; ; ; ; ;
Publication Date:
Research Org.:
National Renewable Energy Lab. (NREL), Golden, CO (United States); SLAC National Accelerator Lab., Menlo Park, CA (United States)
Sponsoring Org.:
USDOE Office of Energy Efficiency and Renewable Energy (EERE), Solar Energy Technologies Office (EE-4S); USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
OSTI Identifier:
1347563
Alternate Identifier(s):
OSTI ID: 1334596
Report Number(s):
NREL/JA-5K00-67423
Journal ID: ISSN 0927-0248
Grant/Contract Number:
AC36-08GO28308; AC02-76SF00515
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
Solar Energy Materials and Solar Cells
Additional Journal Information:
Journal Volume: 160; Journal Issue: C; Journal ID: ISSN 0927-0248
Publisher:
Elsevier
Country of Publication:
United States
Language:
English
Subject:
14 SOLAR ENERGY; 36 MATERIALS SCIENCE; copper-indium-gallium-selenide; CIGS; XAS; chemical bath deposition; surface analysis

Citation Formats

Schwartz, Craig, Nordlund, Dennis, Sokaras, Dimosthenis, Contreras, Miguel, Weng, Tsu-Chien, Mansfield, Lorelle, Hurst, Katherine E., Dameron, Arrelaine, Ramanathan, Kannan, Prendergast, David, and Christensen, Steven T. Soft X-ray absorption spectroscopy investigation of the surface chemistry and treatments of copper indium gallium diselenide (CIGS). United States: N. p., 2017. Web. doi:10.1016/j.solmat.2016.11.003.
Schwartz, Craig, Nordlund, Dennis, Sokaras, Dimosthenis, Contreras, Miguel, Weng, Tsu-Chien, Mansfield, Lorelle, Hurst, Katherine E., Dameron, Arrelaine, Ramanathan, Kannan, Prendergast, David, & Christensen, Steven T. Soft X-ray absorption spectroscopy investigation of the surface chemistry and treatments of copper indium gallium diselenide (CIGS). United States. doi:10.1016/j.solmat.2016.11.003.
Schwartz, Craig, Nordlund, Dennis, Sokaras, Dimosthenis, Contreras, Miguel, Weng, Tsu-Chien, Mansfield, Lorelle, Hurst, Katherine E., Dameron, Arrelaine, Ramanathan, Kannan, Prendergast, David, and Christensen, Steven T. Wed . "Soft X-ray absorption spectroscopy investigation of the surface chemistry and treatments of copper indium gallium diselenide (CIGS)". United States. doi:10.1016/j.solmat.2016.11.003. https://www.osti.gov/servlets/purl/1347563.
@article{osti_1347563,
title = {Soft X-ray absorption spectroscopy investigation of the surface chemistry and treatments of copper indium gallium diselenide (CIGS)},
author = {Schwartz, Craig and Nordlund, Dennis and Sokaras, Dimosthenis and Contreras, Miguel and Weng, Tsu-Chien and Mansfield, Lorelle and Hurst, Katherine E. and Dameron, Arrelaine and Ramanathan, Kannan and Prendergast, David and Christensen, Steven T.},
abstractNote = {The surface and near surface structure of copper-indium-gallium-selenide (CIGS) absorber layers is integral to the producing a high-quality photovoltaic junction. By using X-ray absorption spectroscopy (XAS) and monitoring multiple elemental absorption edges with both theory and experiment, we are able to identify several features of the surface of CIGS as a function of composition and surface treatments. The XAS data shows trends in the near surface region of oxygen, copper, indium and gallium species as the copper content is varied in the films. The oxygen surface species are also monitored through a series of experiments that systematically investigates the effects of water and various solutions of: ammonium hydroxide, cadmium sulfate, and thiourea. These being components of cadmium sulfide chemical bath deposition (CBD). Characteristics of the CBD are correlated with a restorative effect that produces as normalized, uniform surface chemistry as measured by XAS. This surface chemistry is found in CIGS solar cells with excellent power conversion efficiency (<19%). The results provide new insight for CIGS processing strategies that seek to replace CBD and/or cadmium sulfide.},
doi = {10.1016/j.solmat.2016.11.003},
journal = {Solar Energy Materials and Solar Cells},
number = C,
volume = 160,
place = {United States},
year = {Wed Feb 01 00:00:00 EST 2017},
month = {Wed Feb 01 00:00:00 EST 2017}
}

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  • The surface and near surface structure of copper-indium-gallium-selenide (CIGS) absorber layers is integral to the producing a high-quality photovoltaic junction. By using X-ray absorption spectroscopy (XAS) and monitoring multiple elemental absorption edges with both theory and experiment, we are able to identify several features of the surface of CIGS as a function of composition and surface treatments. The XAS data shows trends in the near surface region of oxygen, copper, indium and gallium species as the copper content is varied in the films. The oxygen surface species are also monitored through a series of experiments that systematically investigates the effectsmore » of water and various solutions of: ammonium hydroxide, cadmium sulfate, and thiourea. These being components of cadmium sulfide chemical bath deposition (CBD). Characteristics of the CBD are correlated with a restorative effect that produces as normalized, uniform surface chemistry as measured by XAS. This surface chemistry is found in CIGS solar cells with excellent power conversion efficiency (<19%). The results provide new insight for CIGS processing strategies that seek to replace CBD and/or cadmium sulfide.« less
  • In this study, we present a physics-based analytical model for copper indium gallium diselenide (CIGS) solar cells that describes the illumination- and temperature-dependent current-voltage (I-V) characteristics and accounts for the statistical shunt variation of each cell. The model is derived by solving the drift-diffusion transport equation so that its parameters are physical and, therefore, can be obtained from independent characterization experiments. The model is validated against CIGS I-V characteristics as a function of temperature and illumination intensity. This physics-based model can be integrated into a large-scale simulation framework to optimize the performance of solar modules, as well as predict themore » long-term output yields of photovoltaic farms under different environmental conditions.« less
  • The influence of Cu(In,Ga)Se{sub 2} (CIGSe) surface roughness on the photovoltaic parameters of state of the art devices is reported, highlighting the importance of the roughness of the as-grown CIGSe absorbers on solar cell efficiencies. As-grown CIGSe surface is progressively smoothed using a chemical etch, and characterized by SEM, AFM, XPS, {mu}-Raman spectroscopy, x-ray diffraction (XRD), and reflectivity. The decrease of roughness has no marked influence on crystal structure and surface composition of the absorber. The main effect is that the total reflectivity of the CIGSe surface increases with decreasing roughness. The samples are processed into solar cells and characterizedmore » by current-voltage measurements. While the open circuit voltage (V{sub oc}) and fill factor remain constant, the short circuit current (J{sub sc}) decreases markedly with decreasing roughness, resulting in a reduction of the solar cell efficiency from 14% down to 11%, which exceeds the expected decrease from increased reflectivity. Quantum efficiency and reflectivity measurements on complete cells are performed to analyze those effects. The influence of surface roughness on the theorical effective space charge region and diffusion length is based on a simple theoretical model. This paper discusses the comparison of CIGSe solar cells with n-i-p structures.« less
  • A novel electrochemical setup has been developed for soft x-ray absorption studies of the electronic structure of electrode materials during electrochemical cycling. In this communication we illustrate the operation of the cell with a study of the corrosion behavior of copper in aqueous NaHCO3 solution via the electrochemically induced changes of its electronic structure. This development opens the way for in situ investigations of electrochemical processes, photovoltaics, batteries, fuel cells, water splitting, corrosion, electrodeposition, and a variety of important biological processes.
  • Thermal processing of Cu(In{sub 1{minus}x}Ga{sub x})Se{sub 2} thin-films grown as part of photovoltaic devices on soda-lime glass leads to the incorporation of Na impurity atoms in the Cu(In{sub 1{minus}x}Ga{sub x})Se{sub 2}. Na contamination increases the photovoltaic efficiency of Cu(In{sub 1{minus}x}Ga{sub x})Se{sub 2}-based devices. The purpose of this investigation is to develop a model for the chemistry of Na in Cu(In{sub 1{minus}x}Ga{sub x})Se{sub 2} in an effort to understand how it improves performance. An analysis of x-ray photoelectron spectroscopy data shows that the Na concentration is {approximately}0.1 at.{percent} in the bulk of Cu(In{sub 1{minus}x}Ga{sub x})Se{sub 2} thin films and that themore » Na is bound to Se. The authors propose a model invoking the replacement of column III elements by Na during the growth of Cu(In{sub 1{minus}x}Ga{sub x})Se{sub 2} thin films. Na on In and Ga sites would act as acceptor states to enhance photovoltaic device performance. {copyright} {ital 1997 American Vacuum Society.}« less