Maqsood Ali MughalEnvironmental Sciences Proposal Defense Room No. : 15312:30 PM

Arkansas State University“A Statistical Approach to Optimize Parameters for Electrodeposition of Indium (III) Sulfide Films, Potential Low-Hazard Buffer Layers for Photovoltaic Applications”

November 14, 2014

Why Solar Cells??

3

Rapidly falling prices and gains in efficiencies

4

Federal/state tax incentives, and rebates

5World carbon emissions rate is projected to increase to 11.0 GtC/yr by 2050 [3]

6

Fossil fuels are not renewable energy

Social responsibilit

y

Economic goals

Sustainability

Source: beyond1energy, LLC

Source: beyond1energy, LLC

2

Energy reserves on earth equals energy from just 20 days of sunshine [2]

1Increased energy demand, 18 TW by 2050 [1]

Solar Ce

ll Structu

re

Source: http://www.circuitstoday.com/thin-film-solar-cell Source: Jackson, Philip, et al. March 2014

Role of Buffer Layer in Solar CellsTo form a junction with the absorber layer while admitting a maximum amount of light to the junction region and absorber layer.To protect or passivate the junction material.Provide layer of appropriate thickness and index of refraction that will reduce the overall reflectance.To absorb light energy from only the high-energy end of the spectrum.Must be thin enough and have a large enough bandgap (2.3 eV or more) to let nearly all available light through the interface (junction) to the absorbing layer. 

Photo taken by: John Hall

n-type semiconductorLarge optical bandgap of (2.0-2.3) eV [4].

Stable, high absorption coefficient, and photoconductive [5][6].

Replacement for hazardous CdS, as a window layer in solar cells [7].

Physical properties and structure of In2S3 thin filmsStructure TetragonalColor YellowAppearnce Crystalline solidMelting Point 1050 oCDensity 4450 kg/m3Lattice Parameters a=b=7.619 Å c=32.329 Å

Indium (III) Sulfide (In2S3)

Highest Efficiencies Achieved with In2S3-based Solar Cells Produced by Various Deposition MethodsBuffer Layer Deposition Method Absorber Layer Efficiciency [%] Jsc [mA/cm2] Voc [mV] FF [%] Area (cm2) Reference Institution

In2S3

Sputtering CIGS 16.4 32.5 660 77.5 0.1 Naghavi N. et al. (2010) ZSW/HMI/WSALD CIGS 16.4 31.5 665 78 0.5 Naghavi N. et. al. (2004)   ENSCP/ZSWCBD CIGS 15.7 37.4 574 68.4 0.5 Allsop N.A. et al. (2005) IPE/ASCPVD CIGS 15.4 33.7 628 72.7 0.528 Fraunhofe ISE (2009) Wurth Solar

ILGAR CIGS 14.7 37.4 574 68.4 0.5 Fischer C.-H. et al. (2010) HMIALE CIGS 13.5 30.6 604 73 N/A  D. Lincot et al. (1995) LECAUSP CIGS 13.4 33.4 585 69 N/A  Buecheler S. (2009) LTFP/SFLMTR ED CIGS 9.5 29.3 535 61  N/A Chassaing E. et al. (2011) IRDEP/IREMCSP CuInS2 9.5* 48.2 588 33.5  N/A John T.T. (2005) CUSAT

Deposition Method (Buffer Layer) Absorber Layer Buffer Layer Efficiency [%] Jsc [mA/cm2]Voc [mV] FF [%] Area (cm2) References

ALD CIGS In2S3 16.4 31.5 665 78 0.5 A. Hultqvist, et al. 2007CdTe CdS 16.7 32.8 671 75.8 0.5 Y. Yan, et al. 2012CBD CIGS In2S3 15.7 37.4 574 68.4 0.5 C. D. Lokhande, et al. 1998CIGS CdS 20.8 39.6 581 60.3 0.5 P. Jackson, et al. 2014PVD CIGS In2S3 15.2 29.8 677 75.6 0.528 S. Gall, et al. 2007

CIGS CdS 14 31.4 613 73 0.5 U. P. Singh, et al. 2010Sputtering CuInS2 In2S3 12.2 31.5 665 78 0.1 N. Naghavi, et.al, 2003CuInS2 CdS 9.4 20.3 671 68.9 0.5 A. Grimm, et al. 2008

USP CIGS In2S3 11.9 30.2 543 73 0.3 N. Demirci, et al. 2012CIGS CdS 12.5 30.3 576 73 0.3 Fella, et al. June 2010Electrodeposition CIGSe In2S3 10.4 29.3 535 61 0.5 N. Naghavi, et al. 2011CdTe CdS 10.8 23.6 753 61 0.5 S. K. Das, et al. 1993

In2S3 vs. CdS

Electrode

positio

n1) Straightforward scale-up tolarger areas.2) Low cost, simple apparatuses and reagents; no vacuum required [8].3) Relatively low hazard due to non-gaseous nature.4) Potential for stoichiometry control through variation of deposition voltage and current, and in-situ monitoring of photocurrents.5) Excellent material utilization efficiency [9].

Three-electrode Electrochemical Cell

Side View

Aerial View

Coated-glass substrate (cathode)Reference

electrode

Graphite (anode)

Magnetic stir bar

Teflon cover

Temperature probe

Glass Beaker

Experiment Details Solvent: ethylene glycol, 150 ml Solutes: 0.1 M NaCl, 0.1 M Na2S2O3. 5H2O, 0.05 M InCl3(Sulfur concentration is 0.1 M and 0.15 M) Anode (counter electrode): graphite, 1.25 inch by 1.25 inch. Reference electrode: Ag/AgCl (filled with KCL & C2H6O2) Cathode (working electrode): molybdenum-coated glass, ITO, FTO

Thickness: 0.12 inch Material: SiO2: Mo Target resistivity value of 2.5 – 30 ohms per square Size: 1 inch by 1 inch

Wavenow digital potentiostat: Pine Research Instrumentation Digital hotplate from Fisher Scientific (Isotemp 11-400-49SHP) was used to heat and stir the solution.  Substrates ultrasonically (Cole Parmer 8890) cleaned with acetone for 15 min Distilled water used for rinsing the films* Samples are stored in air-tight plastic boxes/bags to protect the films.

9

10

MM-In2S3-06/16/11-1 MM-In2S3-06/14/11-2MM-In2S3-06/8/2011-9

MM-In2S3-06/2/2011-6

MM-In2S3-04/19/2011-6MM-In2S3-04/06/2011-9

MM-In2S3-03/30/2011-3

MM-In2S3-03/10/2011-8

MM-In2S3-03/09/2011-7MM-In2S3-03/08/2011-5

MM-In2S3-03/07/2011-3 MM-In2S3-02/16/2011-4

MM-IIn2S3-03/03/2011-2MM-In2S3-02/15/2011-2

Voltage Temperatu

re

Time

Composition of Solution

Stir Rate

Current Density

Deposition Parameters

Solvent

Absorbance

Optical Bandga

p

Stoichiometry

Crystalline Structure

Morphology

Thickness

Performance Parameters

Why Taguchi Experimental Design?

Taguchi Methods are statistical methods developed by Genichi Taguchi to improve the quality of manufactured goods, and more recently have also been applied to engineering, biotechnology, etc [10].Two basic goals of Taguchi Methods:

Quality Control Design of Experiments (DOE)

To determine the “best” combination of factors and levels to produce a high quality product. To measure the impact/sensitivity of factors and parameter levels on the characterized performance of a product using statistical analysis tools (Orthogonal Regression, ANOVA, etc.).

Analyzing Experimental Data Once the design of experiments (DOE) has been determined and the trials have been conducted, the measured performance characteristic from each trial can be used to analyze the relative effect of the different parameters. To demonstrate the data analysis procedure, the following orthogonal design arrays (L18, L27, etc.) will be used, but the principles can be transferred to any type of array. The Taguchi Method allows for the use of a noise matrix including external factors affecting the process outcome rather than repeated trials [11].Software:Minitab, Matlab, MS Excel

і = experiment numberu = trial numberNi = number of trials for experiment i

S/N

Collected : 14-Sep-2011 06:15 PMLivetime (s) : 37.16Real time (s) : 38.30Detector : SiliconWindow : SATWTilt (deg) : 0.0Elevation (deg) : 45.0 Azimuth (deg) : 0.0Magnification : 552 XAccelerating voltage ( kV ) : 19.48Process time : 4

EDS Elemental Peaks for In2S3

SEM/EDS Analysis

Spectrum 1

Spectrum 2

Spectrum 3

(a) (b)

Experiment No. 5 and Trial No. 2) (a) SEM image of In2S3 film at 1.21 kX (b) SEM image of scratched-off film on an aluminum stub at 99 X with selected surface area (squares) for EDS analysis

Sulfur to Indium (S/In) Ratios from Energy Dispersive X-ray Spectroscopy (EDS)

UniformityExperiment

No. Taguchi Orthagonal

L27 Array

Sulfur to Indium Ratio (S/In)

Trial 1 Trial 2 Trial 3 Mean

A B C D S/In S/In S/In S/In

■ 1 1 1 1 1 1.432 1.462 1.447 1.447■ 2 1 1 2 2 1.459 1.468 1.464 1.464■ 3 1 1 3 3 1.49 1.535 1.513 1.513■ 4 1 2 1 2 1.473 1.35 1.411 1.411■ 5 1 2 2 3 1.522 1.47 1.481 1.49■ 6 1 2 3 1 1.432 1.482 1.457 1.457■ 7 1 3 1 3 1.465 1.452 1.459 1.459■ 8 1 3 2 1 1.374 1.43 1.402 1.402■ 9 1 3 3 2 1.428 1.484 1.456 1.456■ 10 2 1 1 2 1.381 1.44 1.411 1.411■ 11 2 1 2 3 1.442 1.418 1.43 1.43■ 12 2 1 3 1 1.393 1.454 1.424 1.424■ 13 2 2 1 3 1.743 1.853 1.798 1.798□ 14 2 2 2 1 1.547 1.238 1.393 1.393□ 15 2 2 3 2 1.448 1.269 1.358 1.358□ 16 2 3 1 1 2.886 2.051 2.468 2.468□ 17 2 3 2 2 2.434 1.966 2.2 2.2□ 18 2 3 3 3 2.478 2.014 2.246 2.246□ 19 3 1 1 3 2.329 1.449 1.889 1.889□ 20 3 1 2 1 2.507 2.398 2.452 2.452□ 21 3 1 3 2 1.384 1.469 1.426 1.426□ 22 3 2 1 1 1.344 1.371 1.340 1.354□ 23 3 2 2 2 1.357 1.327 1.342 1.342□ 24 3 2 3 3 2.722 2.237 2.48 2.48□ 25 3 3 1 2 2.007 2.817 2.412 2.412□ 26 3 3 2 3 1.448 1.509 1.478 1.478□ 27 3 3 3 1 1.429 1.539 1.484 1.484

Output Re

sponse

Table Levels A, Deposition Voltage (V)

B, Deposition Time (min.) C, Composition of Solution (COS)

D, Deposition Temperature (oC)1 34.79 31.61 24.68 25.042 23.21 25.73 30.92 30.133 23.63 24.52 26.15 27.18▲ 11.58 7.08 6.23 5.10Rank 1 2 3 4

Output Response Table for Signal-to-Noise Ratios

Optimized Electrodeposition Parameters

-0.8V-0.7V-0.6V

35

30

25

9min6min3min

321

35

30

25

170C160C150C

Deposition Voltage (E)

Mean o

f SN ratios

Deposition Time (D-Time)

Composition of Solution (COS) Deposition Temperature (D-Temp)

Main Effects Plot for SN ratiosData Means

Signal-to-noise: Nominal is best (10*Log10(Ybar**2/s**2))

(V)

Orthogonal Regression Analysis (S/In vs. Deposition Voltage) Plot of S/In Ratio vs. Deposition Voltage with Fitted Line

S/In

Rati

o

Deposition Voltage (V)

Spectrum In stats. O Si S Mo In Total S/InSpectrum 1 Yes 6.54 0.00 54.1 3.12 36.24 100.00 1.493Spectrum 2 Yes 0.00 0.00 56.65 8.36 37.51 100.00 1.51Spectrum 3 Yes 0.00 0.00 55.18 7.27 37.54 100.00 1.471Spectrum 4 Yes 14.48 0.00 50.65 2.82 33.75 100.00 1.5Spectrum 5 Yes 0.00 0.00 58.32 0.00 40.5 100.00 1.443Spectrum 6 Yes 0.00 0.00 59.8 0.00 39.91 100.00 1.498Spectrum 7 Yes 4.21 0.00 57.49 0.00 38.30 100.00 1.501Spectrum 8 Yes 0.00 0.00 60.28 0.1 39.71 100.00 1.53

Mean 1.493Max. 14.48 0.00 60.28 8.36 40.5Min. 0.00 0.00 50.65 0.00 33.75

MM-In2S3-09/01/11-6

EDS Data for In2S3 Films Grown at Optimal Values Obtained from Taguchi Analysis

Morphology- Scanning Electron Microscopy (SEM)

Electrodeposited at -0.685 V for 6 min. and at -0.7 V for 40

min. (repeated trials)

Pulse-plating (-0.8 V with 10 sec. delay) at120 oC for 50 min.

Mo

Pulse-plating (-0.685 V with 10 sec. delay) at 70 oC for

95 min. FTO

Pulse-plating (-0.7 V with 15 sec. delay) at 150 oC for 48

min. FTO

Pulse-plating (-0.7 V with 10 sec. delay) at 80 oC for 75 min.

ITO

Indium sulfide ring formation from

sodium thiosulfate as sulfur source-ITO

Electrodeposited at -0.685 V for 4 min with ethylene

glycol solvent

Current density: 0.75 mA/cm2

Electrodeposited at -0.7 V for 15 min.

(sodium thiosulfate as sulfur source)

Electrodeposited at -0.7 V for 50 min.

at 160 oC

JH: Electrodeposited at -0.8 V for 30 min

in formamide solvent

Current density: 1.25 mA/cm2

Current density: 1.5 mA/cm2

Current density: 1 mA/cm2

Low resistance substrate-ITO at150

oC

Electrodeposited at -0.7 V for 50 min. at 160 oC

Indium sulfide ring formation from sodium

thiosulfate as sulfur source-ITO

Electrodeposited at -0.7 V for 15 min. (sodium thiosulfate as sulfur

source)

Post-annealed electrodeposition

Post-annealed electrodeposition (repeated trials)

Post-annealed electrodeposition

Post-annealed electrodeposition (repeated trials)

Horizontally positioned

substrate-Mo

Horizontally positioned substrate-Mo Low resistance substrate-ITO

at150 oC

Pulse-plating (-0.685 V with 10 sec. delay) at 70 oC for 95

min. FTO

Pulse-plating (-0.7 V with 15 sec. delay) at 150 oC for 48

min. FTO

Pulse-plating (-0.7 V with 10 sec. delay) at 80 oC for 75

min. ITO

Electrodeposited at -0.685 V for 6 min. and at -0.7 V for 40 min. (repeated trials)

Electrodeposited at -0.685 V for 4 min using ethylene glycol

solvent

JH: Electrodeposited at -0.8 V for 30 min in formamide solventCurrent density:

0.75 mA/cm2

Current density: 1.25 mA/cm2

Current density: 1.5 mA/cm2

Pulse-plating (-0.8 V with 10 sec. delay) at120 oC for 50 min. Mo

Current density: 1mA/cm2

Reported Papers on Electrodeposition of Semiconductor Thin Films with Crack MorphologySemiconductor Material Electrolyte Potential Cause for Cracks Reference

CdS Organic Thickness and current density Fulp & Taylor, 1985CdS DEG-water mixtures Incorporation of solutes with solvent/addition agent Fulp & Taylor, 1985Si Ionic Liquid Thickness, substrates, deposition voltage Oskam et. al., 2001

Bi2S3 Aqueous Solvents  A. Begum, et al. 2011CIGS Aqueous % composition of precursor chemicals  V. S. Saji, et al. 2011CdS Organic Solvent and piezoelectric effect  M. N. Mammadov, et al. 2012Cu-Ga-Se Aqueous Incorporation of solutes with solvent/addition agent and % composition of precursor solutions Y. Oda, et al. 2008 

Cu Aqueous Surface contamination H. Lou & Y. Huang, 2006 CdSe Aqueous Substrates R. I Chowdhury, et al. 2011 

Crack Morphologies from Solution-Based Deposition TechniquesCu-Ga-S (Y. Oda, et al. 2008)

CZTS(M. Jiang and X. Yan 2008)

TiO2 (A. R. Santos, et al. 2013)

ZnO (C. Liehiran, et al. 2007)

-FeƳ 2O3 (AT. Ngo, et al. 2013)

ZnO:Cl on CIGS/In2S3 (J. Rousset, et al. 2011)

TiO2 (G. Xue, et al. 2012)

In2S3 (K. Otto, et al. 2011)In2S3 (E. Aydin, et al. 2012)

Control Deposition Parameters and LevelsLevels “A” Bath Composition

“B” Current Density (mA/cm2)“C” Substrate “D” Deposition Time (min)

“E” Deposition Temperature (oC)1 0.1M S + 0.05M InCl3 + 0.1M NaCl 0.75 Mo 5 140

2 0.1M S + 0.1M Na2S2O3.5H2O +0.05 M InCl3 + 0.1M NaCl 1.25 ITO 10 150

3 -----  1.75  FTO 15 160

Digital Imaging Analysis: Fracture and Buckling Analysis Software for Crack Density Calculation(Area of interest = 2100.69 µm2)

Deposition ParametersLevels A, Bath Composition

B, Current Density (mA/cm2) C, Substrate D, Deposition Time (min)E,Deposition Temperature (oC)

1 0.1989 0.0684 0.16 0.1880 0.12842 0.1772 0.2847 0.2721 0.2002 0.22323 --- 0.1916 0.1758 0.1754 0.2005▲ 0.0218 0.2162 0.1121 0.0247 0.0948

Rank 5 1 2 4 3

Output Response Table for Means(Mean Crack Density)

Optimized Electrodeposition Parameters

EDS Data for Indium Sulfide Films Electrodeposited at 0.75 mA/cm2

As-deposited Annealed 200oC Annealed 300oC Annealed 400 oCElement Atomic%Carbon (C) 24.3 8.93 0 19.36Oxygen (O) 19.99 32.34 17.85 58.17Aluminum (Al) 0 0 0 0.19

Sulfur (S) 32.33 34.05 49.21 11.21Indium (In) 23.38 24.68 32.94 11.08

S/In Ratio 1.38 1.37 1.49 1.01

Optical Bandgap Plots (ITO)

X-Ray Diffraction Pattern

Future Worki. Study and improve the crystalline structure of In2S3 films as a function of heat treatment and then compare the results from conventional oven-based heating versus laser annealing, and intense pulse light annealing.ii. Use the X-ray mapping feature on the EDS to study elemental distributions over the surface area of the electrodeposited In2S3 films.iii. Study the effect of performance parameters as a function of thickness of In2S3 films.iv. Prepare/complete three potential papers for publication:- Effect of different heat treatments on the crystalline structure of electrodeposited In2S3 films.- Indium Sulfide: A Review

(The paper will feature all of the In2S3-based solar cells with record efficiencies produced with various deposition techniques).- Life Cycle Assessment (LCA) of In2S3-based solar cells.

1) M. A. Mughal, M. J. Newell, R. Engelken, B. Ross Carroll, J. Bruce Johnson, et al., "Statistical analysis of electroplated indium (III) sulfide (In2S3) films, a potential buffer material for PV (heterojunction solar cell) systems, using organic electrolytes," Nanotechnology 2013: Bio Sensors, Instruments, Medical, Environment, and Energy,3. Technical Proceedings of the 2013 NSTI Nanotechnology Conference, Washington, DC, pp. 523-527, May 12-16, 2013.2) M. A. Mughal, M. J. Newell, R. Engelken, B. Ross Carroll, J. Bruce Johnson, et al., “Morphological and compositional analysis of electrodeposited In2S3 Films” Proceedings of the 40th IEEE Photovoltaic Specialists Conference (PVSC), Denver, CO, pp. 1322-1326, June 07-14, 2014.3) M. A. Mughal, M. J. Newell, R. Engelken, B. Ross Carroll, J. Bruce Johnson, et al., “Optimization of the electrodeposition parameters to improve the stoichiometry of In2S3 films for solar applications using the Taguchi Method, Journal of Nanomaterials, vol. 2014, pp. 1-10, 2014.4) Paper submitted (October, 2014) to IEEE Journal of Photovoltaics (under review) on “Morphological and compositional analysis of electrodeposited In2S3 films”.

Scholarly Publications

Publication: Journal of Nanomaterials

1) Poster presentation at  Fourth Annual Renewable Energy Conference (Sep., 2014) on “Update on Semiconductor Film Electrodeposition Research at Arkansas State University”, Arkansas State University-Jonesboro, AR.2) Posterl presentation at ASSET Initiative Annual Meeting (Sep., 2014) on “Update on Semiconductor Film Electrodeposition Research at Arkansas State University ”, Little Rock, AR .3) Poster presentation at 40th IEEE PVSC Conference (June, 2014) on “Morphological and Compoitional Analysis of Electrodeposited In2S3 Films”, Denver, CO.4) Poster presentation at TechConnect Conference (May, 2013) on “Statistical Analysis of Electroplated Indium (III) Sulfide (In2S3) Films, a Potential Buffer Material for PV (Heterojucntion Solar Cells) Systems, using Organic Electrolytes”, Washington, DC.5) Poster presentation at Create@State (Apr., 2013) on “Innovations in Semiconductor Electrodeposition”, Arkansas State University, Jonesboro, AR.6) Poster presentation at Arkansas State Capitol (Feb., 2013) on “CdTe/In2S3 Solar Cells by Electrodepostion and Evaporation”, Little Rock, AR.7) Oral presentation at ASSET Initiative Annual Meeting (Aug., 2012) on “Progress and Challenges in Electrodeposition of Indium (III) Sulfide (In2S3) Films from Organic Electrolytes for Potential Solar Cell Use”, Springdale, AR.8) Oral presentation at Arkansas Academy of Science ( Apr., 2012) on “Taguchi Analysis and Characterization of Electrodeposited Indium Sulfide Films for Use as Potential Buffer Layers in Solar Cells”, Magnolia, AR (Third prize in the graduate physics category).9) Oral presentation at Create@State (Apr., 2012) on “Rest Potential-Based Electrodeposition of Metal Sulfide Films”, Arkansas State University, Jonesboro, AR.10) Poster presentation at Arkansas State Capitol (Feb., 2012) on “Progress in Electrodeposition of Indium Sulfide and Copper Indium Disulfide”, Little Rock, AR.11) Poster presentation at ASSET Initiative Annual Meeting (July, 2011) on “Research at Arkansas State University Optoelectronic Materials Research Laboratory”, Heber Springs, AR.12) Oral presentation at Electronic Materials Conference EMC (June, 2011) on “Electrodeposition of Indium Sulfide Films from Organic Electrolyte”, University of Santa Barbara, Santa Barbara, CA.13) Oral presentation at Create@State (Apr., 2011) on “Electrodeposition of Indium Sulfide from Organic Electrolytes”, Arkansas State University, Jonesboro, AR.14) Oral presentation at Arkansas Academy of Science ( Apr., 2011) on “Elemental Sulfur-based Electrodeposition of Indium Sulfide Films”, Monticello, AR (First Prize in graduate category).

Scholarly Activities

I acknowledge the gracious support provided by Arkansas State University, National Science Foundation grant EPS-1003970 administered by the Arkansas Science and Technology Authority, and NASA grant NNX09AW22A administered by the Arkansas Space Grant Consortium.  Dr. Alan Mantooth, Kathy Kirk, Dr. Greg Salamo, Dr. Omar Manasreh, Dr. Alex Biris, Dr. Tansel Karabacak, Dr. Hyewon Seo, and other collaborators at the University of Arkansas (Fayetteville, Little Rock, and Pine Bluff campuses) are also thanked, as are Dr. Keith Hudson and Laura Holland at ASGC, and Dr. Gail McClure, Cathy Ma, and Marta Collier at ASTA. The authors are also grateful for the ongoing support provided by Arkansas State University, particularly Dr. David Beasley, Dr. Rick Clifft, Dr. Paul Mixon, Dr. William Burns, Dr. Tom Risch, Dr. Tanja McKay, Dr. John Pratte, and Dr. Andrew Sustich. Thanks also go to Dr. Richard Segall and Dr. Ilwoo Seok for an introduction to the Taguchi Method, and Dr. Trauth for the use of the SEM/EDS unit.Particular thanks go to my advisor, Dr. Robert Engelken, my student research colleagues, and all of you, my Ph.D. committee members. Thank You !

Acknowledgements

References1) Roy L. Nersesian. 2007. Energy for the 21st Century: A Comprehensive Guide to Conventional and Alternative Sources / Roy L. Nersesian. n.p.: Armonk, N.Y.: M.E. Sharpe. 2) George Greenstein. 2013. Understanding the Universe: An Inquiry Approach to Astronomy and the Nature of Scientific Research. Cambridge University Press.3) Dr. Pieter Tans, NOAA/ESRL (www.esrl.noaa.gov/gmd/ccgg/trends/), and Dr. Ralph Keeling, Scripps Institution of Oceanography (scrippsco2.ucsd.edu/). Available at: http://www.esrl.noaa.gov/gmd/ccgg/trends/4) M. Lajnef and H. Ezzaaouia. 2009. “Structural and Optical Studies of Indium Sulfide Thin Films Prepared by Sulfurization of Indium Thin Films.” The Open Applied Physics Journal, 2, pp. 23-26.5) A. M. Abdel Haleem, M. Sugiyama, and M. Ichimura. 2012. “Sulphurization of the Electrochemically Deposited Indium Sulphide Oxide Thin Film and its Photovoltaic Applications.” Materials Sciences and Applications, vol. 3, no. 11, p. 802.6) T. T. John, S. Bini, Y. Kashiwaba, T. Abe, Y. Yasuhiro, C. Kartha, and K. Vijaykumar. 2003. “Characterization of Spray Pyrolysed Indium Sulfide Thin Films.” Semiconductor Science and Technology, vol. 6, pp. 491-500.7) Walther Schwarzacher. 2006. “Electrodeposition: A Technology for the Future.” The Electrochemical Society Interface, pp. 32-33.8) Milan Krenzelok, Petr Rychlovsky, Michael Volnya, and Jaroslav P. Matouse. 2003. "Evaluation of In-Situ Electrodeposition Technique in Electrothermal Atomic Absorption Spectrometry." Analyst , 128.3, pp. 293-300.9) I. N. Vuchkov and L. N. Boyadjieva. 2001. Quality Improvement with Design of Experiments: A Response Surface Approach. Kluwer Academic Publishers. Dordrecht, 2001.10) D. M. Steinberg and D. Burnsztyn. 1998. “Noise Factors, Dispersion Effects, and Robust Design.” Statistica Sinica, vol. 8, pp. 67-85.