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Title: Insights into cadmium diffusion mechanisms in two-stage diffusion profiles in solar-grade Cu(In,Ga)Se{sub 2} thin films

Abstract

Cadmium diffusion experiments were performed on polished copper indium gallium diselenide (Cu(In,Ga)Se{sub 2} or CIGS) samples with resulting cadmium diffusion profiles measured by time-of-flight secondary ion mass spectroscopy. Experiments done in the annealing temperature range between 275 °C and 425 °C reveal two-stage cadmium diffusion profiles which may be indicative of multiple diffusion mechanisms. Each stage can be described by the standard solutions of Fick's second law. The slower cadmium diffusion in the first stage can be described by the Arrhenius equation D{sub 1} = 3 × 10{sup −4} exp (− 1.53 eV/k{sub B}T) cm{sup 2} s{sup −1}, possibly representing vacancy-meditated diffusion. The faster second-stage diffusion coefficients determined in these experiments match the previously reported cadmium diffusion Arrhenius equation of D{sub 2} = 4.8 × 10{sup −4} exp (−1.04 eV/k{sub B}T) cm{sup 2} s{sup −1}, suggesting an interstitial-based mechanism.

Authors:
; ;  [1];  [2]; ;  [1]
  1. Colleges of Nanoscale Science and Engineering, SUNY Polytechnic Institute, Albany, New York 12203 (United States)
  2. (United States)
Publication Date:
OSTI Identifier:
22486190
Resource Type:
Journal Article
Resource Relation:
Journal Name: Applied Physics Letters; Journal Volume: 107; Journal Issue: 23; Other Information: (c) 2015 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; 71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; ANNEALING; ARRHENIUS EQUATION; CADMIUM; COPPER; DIFFUSION; GALLIUM; INDIUM; ION MICROPROBE ANALYSIS; MASS SPECTROSCOPY; THIN FILMS; TIME-OF-FLIGHT METHOD; VACANCIES

Citation Formats

Biderman, N. J., Sundaramoorthy, R., Haldar, Pradeep, U.S. Photovoltaic Manufacturing Consortium, Albany, New York 12203, Novak, Steven W., and Lloyd, J. R. Insights into cadmium diffusion mechanisms in two-stage diffusion profiles in solar-grade Cu(In,Ga)Se{sub 2} thin films. United States: N. p., 2015. Web. doi:10.1063/1.4937000.
Biderman, N. J., Sundaramoorthy, R., Haldar, Pradeep, U.S. Photovoltaic Manufacturing Consortium, Albany, New York 12203, Novak, Steven W., & Lloyd, J. R. Insights into cadmium diffusion mechanisms in two-stage diffusion profiles in solar-grade Cu(In,Ga)Se{sub 2} thin films. United States. doi:10.1063/1.4937000.
Biderman, N. J., Sundaramoorthy, R., Haldar, Pradeep, U.S. Photovoltaic Manufacturing Consortium, Albany, New York 12203, Novak, Steven W., and Lloyd, J. R. Mon . "Insights into cadmium diffusion mechanisms in two-stage diffusion profiles in solar-grade Cu(In,Ga)Se{sub 2} thin films". United States. doi:10.1063/1.4937000.
@article{osti_22486190,
title = {Insights into cadmium diffusion mechanisms in two-stage diffusion profiles in solar-grade Cu(In,Ga)Se{sub 2} thin films},
author = {Biderman, N. J. and Sundaramoorthy, R. and Haldar, Pradeep and U.S. Photovoltaic Manufacturing Consortium, Albany, New York 12203 and Novak, Steven W. and Lloyd, J. R.},
abstractNote = {Cadmium diffusion experiments were performed on polished copper indium gallium diselenide (Cu(In,Ga)Se{sub 2} or CIGS) samples with resulting cadmium diffusion profiles measured by time-of-flight secondary ion mass spectroscopy. Experiments done in the annealing temperature range between 275 °C and 425 °C reveal two-stage cadmium diffusion profiles which may be indicative of multiple diffusion mechanisms. Each stage can be described by the standard solutions of Fick's second law. The slower cadmium diffusion in the first stage can be described by the Arrhenius equation D{sub 1} = 3 × 10{sup −4} exp (− 1.53 eV/k{sub B}T) cm{sup 2} s{sup −1}, possibly representing vacancy-meditated diffusion. The faster second-stage diffusion coefficients determined in these experiments match the previously reported cadmium diffusion Arrhenius equation of D{sub 2} = 4.8 × 10{sup −4} exp (−1.04 eV/k{sub B}T) cm{sup 2} s{sup −1}, suggesting an interstitial-based mechanism.},
doi = {10.1063/1.4937000},
journal = {Applied Physics Letters},
number = 23,
volume = 107,
place = {United States},
year = {Mon Dec 07 00:00:00 EST 2015},
month = {Mon Dec 07 00:00:00 EST 2015}
}
  • A Cu-Ga(66 at.{percent}) alloy target was employed for enhancing the gallium content in CuIn{sub 1{minus}x}Ga{sub x}Se{sub 2} films prepared by two Se-vapor selenizations of metallic precursors. Combination with a Cu-Ga(22 at.{percent}) sputtering target allowed preparation of CuIn{sub 1{minus}x}Ga{sub x}Se{sub 2} films with a graded profile. Gallium content Ga{sub x} near the surface was raised to the range 0.28{endash}0.32, while an even higher amount of gallium of up to 0.40 was obtained in the bulk of the films. Efficiency of solar cells prepared from CuIn{sub 1{minus}x}Ga{sub x}Se{sub 2} films with moderately enhanced gallium content was 8.5{percent}. Higher gallium proportions seem tomore » be correlated with the formation of Cu-rich phases, surface inhomogeneities, and possibly a highly resistive phase. This combined with inferior crystallinity deteriorated solar cell efficiency. {copyright} {ital 1997 American Institute of Physics.}« less
  • Defect chalcopyrite thin films of Cu(In,Ga){sub 2}Se{sub 3.5} were prepared by rf sputtering from stoichiometric CuIn{sub x}Ga{sub 1{minus}x}Se{sub 2} (x=0.6) and Na mixture target. The composition of the thin films fabricated in the ratio of [Na]/[Cu(In,Ga)Se{sub 2}] above 5{percent} was changed from the stoichiometric composition of Cu(In,Ga)Se{sub 2} to Cu-poor one, and identified as Cu:(In+Ga):Se=1:2:3.5. From the results of x-ray diffraction, the lattice parameters of these thin films were slightly smaller than that of Cu(In,Ga)Se{sub 2} and, besides the peaks appearing for chalcopyrite structure Cu(In,Ga)Se{sub 2}, the additional peak was observed. The optical band gap is increased from 1.24 tomore » 1.36 eV with increasing the [Na]/[Cu(In,Ga)Se{sub 2}] ratio from 0{percent} to 10{percent} in the target. These films showed n- or p-type conduction. {copyright} {ital 1997 American Institute of Physics.}« less
  • The morphology of sequentially sputtered metallic precursors and CuIn{sub 1{minus}{ital x}}Ga{sub {ital x}}Se{sub 2} thin films prepared using a novel two-stage selenization process was found to change from initially very smooth layers with a root-mean-square (rms) surface roughness of {lt}10 A to coalescing grains with a fine ({similar_to}200 A) subgrain structure, three-dimensional {similar_to}9000 A size islands, and finally to compact, well-faceted, large {similar_to}1 {mu}m grain-size CuIn{sub 1{minus}{ital x}}Ga{sub {ital x}}Se{sub 2} thin films with a rms roughness of 950--1500 A. {ital In} {ital situ} homogenization of Cu-rich precursors prior to the first selenization and a maximum selenization temperature of 550--560more » {degree}C that provided beneficial fluxing action of copper selenide improved the morphology of completed CuIn{sub 1{minus}{ital x}}Ga{sub {ital x}}Se{sub 2} thin films and the photovoltaic conversion efficiency of the solar cells. {copyright} {ital 1995} {ital American} {ital Vacuum} {ital Society}« less
  • Cadmium-free Cu(In,Ga)Se{sub 2} (CIGS) thin-film solar cells with a MgF{sub 2}/ZnO:Al/CBD-ZnS/CIGS/Mo/SLG structure have been fabricated using chemical bath deposition (CBD)-ZnS buffer layers and high-quality CIGS absorber layers grown using molecular beam epitaxy (MBE) system. The use of CBD-ZnS, which is a wider band gap material than CBD-CdS, improved the quantum efficiency of fabricated cells at short wavelengths, leading to an increase in the short-circuit current. The best cell at present yielded an active area efficiency of 16.9% which is the highest value reported previously for Cd-free CIGS thin-film solar cells. The as-fabricated solar cells exhibited a reversible light-soaking effect undermore » AM 1.5, 100 mW/cm{sup 2} illumination. This paper also presents a discussion of the issues relating to the use of the CBD-ZnS buffer material for improving device performance.« less
  • Cu(In,Ga)Se 2(CIGS) photovoltaic absorbers frequently develop Ga gradients during growth. These gradients vary as a function of growth recipe, and are important to device performance. Prediction of Ga profiles using classic diffusion equations is not possible because In and Ga atoms occupy the same lattice sites and thus diffuse interdependently, and there is not yet a detailed experimental knowledge of the chemical potential as a function of composition that describes this interaction. Here, we show how diffusion equations can be modified to account for site sharing between In and Ga atoms. The analysis has been implemented in an Excel spreadsheet,more » and outputs predicted Cu, In, and Ga profiles for entered deposition recipes. A single set of diffusion coefficients and activation energies are chosen, such that simulated elemental profiles track with published data and those from this study. Extent and limits of agreement between elemental profiles predicted from the growth recipes and the spreadsheet tool are demonstrated.« less