Thermo Fisher Scientific, East Grinstead, UK Thermo Fisher ....pdf · Dr. Tim Nunney. Thermo Fisher...

Dr. Tim NunneyThermo Fisher Scientific, East Grinstead, UKDr. Nick BullossThermo Fisher Scientific, Madison, WI, USADr. Harry Meyer IIIOak Ridge National Laboratory, TN, USA

2

Introduction• New materials create new characterization challenges• Full characterization requires a variety of experimental techniques

Presenter

Presentation Notes

List materials challenges – adhesion, diffusion, layer composition, corrosion, nanostructuring, catalyst design etc. Even simplest items can have huge design challenges (gore-tex)

3

Introduction

• Techniques need to be chosen that provide complimentary information• Elemental and chemical composition• Molecular “fingerprinting”• Composition with increasing depth• Surface structure• Morphology

XPS Surface Analysis Microanalysis

Presenter

Presentation Notes

XPS – surface sensitivity, chemical state information, UHV technique, solid samples EDS – elemental information, micron info depth, high spatial resolution

4

Introduction to X-ray Microanalysis

In an electron column, electrons are accelerated through an electric field, acquiring kinetic energy.

The energy is transferred to the sample

Yields a variety of signals for analysis

5

EDS Basic Overview

Energy Dispersive X-Ray Spectroscopy (EDX / EDS)

Analysis of elemental content of micro-volumes using non-destructive techniques.

Based on inner electron transitions between inner atomic shells.

Energetic electron from an electron column dislodges an orbital electron.

Electron from a higher energy shell fills the vacancy, losing energy in the process.

The lost energy appears as emitted radiation of energy (characteristic X-Ray).

6

Electron Beam & Sample Interaction

Interaction Volume

The volume in which the primary electrons interact with a sample

As electrons interact with the sample, they are scattered and spread.

7

Properties of X-Rays

The relationship between Energy, Frequency, and Wavelength may be expressed by one formula

E is the Energy of the radiation

F is the Frequency of the radiationc is the speed of light 3 x 1010 cm/second

is the Wavelength of the radiation

h is Planck’s constant 4.135 x 10-15 eV-sec = 6.625 x 10-27 erg-sec

8

Detectors

Energy-dispersive detectors (EDS)

• Collect the full range of x-ray energies simultaneously

Wavelength-dispersive detectors (WDS)

• Collect one element at a time via a diffracting crystal

9

Definition of a surface

Bulk

Surface (1 nm) 3 atomic layers

The modified layer is often far too thin to be characterized

with most techniques.

The extreme surface sensitivity of XPS ensures that only the top few nanometers of the

sample are analyzed.

Ultra-thin film (1 to 10 nm) 3 - 30 atomic layers

Thin Film (10 nm to 2µm) 30 - 600 atomic layers

Note: Approximate layer thickness only. Actual values depend upon materials

XPS surface analysis• What is a surface?

• XPS measures

Surfaces using XPS and angle resolved XPS

Ultra-thin films using XPS and angle resolved XPS (ARXPS)

Thin films using XPS in combination with sputter profiling

Presenter

Presentation Notes

Let’s begin by asking ourselves the question, ‘what is a surface’? As far as XPS is concerned we can think of a surface in three ways. When talking literally about the surface, an XPS user is generally referring to the top 1 nm of the sample, which comprises around 3 atomic layers. This region of the surface can be analysed non-destructively using XPS and angle resolved XPS. Ultra-thin films are increasingly used in a variety of industries and applications. This definition of ‘surface’ refers to a region between 1 nm and 10 nm thick, comprising between 3 and 30 atomic layers. Again, XPS and angle resolved XPS could be used to non-destructively analyse this region. The final definition of surface refers to a region 10 nm to 2 microns thick. This definition of surface would include a thicker film coating deposited on a ceramic substrate, for example. To analyse this kind of film, we need to combine XPS analysis with sputter profiling, where we etch away portions of the surface to reveal the underlying structure.

10

XPS instrumentation

Hemispherical analyser

Detector

Ion gun

Flood gun

X-ray source

Monocrystal

Electron transfer lens

• UHV System• Ultra-high vacuum keeps surfaces clean• Allows longer photoelectron path length

• X-ray source• Typically Al Ka radiation• Monochromated using quartz crystal

• Low energy electron flood gun• Low energy e- (and possibly Ar+)• Analysis of insulating samples

• Ion gun• Typically noble gas ions• Sample cleaning• Depth profiling

11

• Surface is composed of atoms• Electrons surround the nucleus of an atom,

occupying orbitals at different energies• Surface is irradiated with X-rays from a photon

source• X-rays cause electrons to be ejected

(photoelectrons)• Kinetic energy, KE, of photoelectrons is

measured by an analyser• The binding energy, BE, of the electrons is

deduced from the kinetic energy and photon energy

• Binding energy depends upon• Element• Orbital from which electron was ejected• Chemical state of the element

Basic XPS theory

Photoelectron ejected

X-rays

BE = h

- KE

01002003004005006007008009001000110012001300Binding Energy (eV)Kinetic Energy (eV)

NaCl

Presenter

Presentation Notes

We have seen that the various regions of the surface are comprised of different numbers of atomic layers and atoms. XPS is an electron spectroscopy that is based on the fact that these atoms are orbited by electrons which exist at discrete energies. When a surface is irradiated with X-rays, which typically come from an aluminium source, electrons are ejected from the atoms. The energies of these so-called photoelectrons can be measured by an analyser and then correlated with the energy they originally had whilst in the atom. The energy the electrons originally had in the atom is referred to as the ‘binding energy’. The binding energy is characteristic of the element from which the electron came as well as the specific orbital it occupied in the atom. The fact that the binding energy is also characteristic of the chemical state of the element makes XPS unique in the context of surface analysis.

12

Surface analysis and XPS• Elemental identification

• Which elements are present?• Can detect all elements except for H

• Elemental quantification• How much of an element is present?

Detection limit >0.05% for most elements

Allows determination of stoichiometry

Cl S

Zn

P

020040060080010001200

Binding energy / eV

Elemental identification of tribology sample

Fe

F

O

Ca

C

Zn

Elemental identification

Element At% P 0.29 S 0.29 Cl 0.22 C 15.96 Ca 14.12 O 57.73 F 1.50 Fe 6.74 Zn 3.03 Mg 0.12

Presenter

Presentation Notes

Elemental identification Which elements are present? Can detect all elements except for H Elemental quantification How much of an element is present? Detection limit >0.05% for most elements Allows determination of stoichiometry

13

• Elemental identification• Which elements are present?• Can detect all elements except for H



Allows determination of stoichiometry• Chemical state identification and quantification

• Bonding states for each element• Chemical structure

Surface analysis and XPS

O

OO

O n

Poly(ethylene terephthalate), PET

280285290295

Binding energy / eV

Carbon

High energy resolution spectroscopy

CC CC

Chemical state identification

14

526531536541

Binding energy / eV

• Elemental identification• Which elements are present?• Can detect all elements except for H



Allows determination of stoichiometry• Chemical state identification and quantification

• Bonding states for each element• Chemical structure

Surface analysis and XPS

O

OO

O n

Poly(ethylene terephthalate), PET

High energy resolution spectroscopy

Oxygen

CCCC

Chemical state identification

Case Study 1: Membrane electrode assembly

16

MEA fuel cell Introduction

Schematic of polymer electrolyte membrane

MEA fuel cell

• Energy/environmental application• Fuel cells for clean conversion of hydrogen• 1Proton exchange membrane fuel cell (PEMFC)

• High conversion efficiency and low/zero pollution• Low operating temperature and relatively quick start-up

• Membrane Electrode Assembly (MEA) is important component of PEMFC

• Active layer of platinum/carbon black catalyst with polymeric adjacent layers

• Practical problem• Diffusion of Pt into adjacent polymer layers would reduce

Pt/C catalytic effect• Solution

• XPS imaging of sample

ULAM (ultra low angle microtomy) sample preparation to allow imaging of nanoscale layers

Quantitative elemental and chemical state mappingK-Alpha optical image of ULAM- prepared MEA fuel cell

1Korean J Chem Eng, 23(4), 555-559 (2006)

Pt/CPt/C

NafionNafion

Presenter

Presentation Notes

Proton exchange membrane fuel cells are devices for the production of electricity from the electrochemical reaction of hydrogen and oxygen, with potential applications as diverse as running cars to powering small electronic devices. The fuel cells are particularly attractive because they have a high conversion efficiency and they are environmentally very clean at the point of use. In contrast to the solid oxide fuel cells discussed later in this presentation, current devices are already able to operate at low temperature and as such, they don’t have a long start up time. One of the components of a proton exchange fuel cell is the Membrane Electrode Assembly (or MEA). The MEA has layers of platinum in carbon black, which catalyze the reaction of hydrogen and oxygen. When manufacturing or developing an MEA, the aim is to maximize the surface area of platinum that is electrically connected to the conducting support: any loss of surface area decreases the efficiency of the device. Platinum loss can sometimes occur when high currents effectively corrode the carbon-black support liberating the active metal allowing it to migrate from the electrode surface to the adjacent polymer electrolyte (which is typically Nafion). Additionally, the presence of platinum in the Nafion will hinder hydrogen ion mobility in the electrolyte. In this work, XPS is used to analyze an MEA and determine if platinum has migrated from the catalytically active layers into the adjacent Nafion electrolyte.

17

MEA fuel cell Chemical analysis of Nafion

MEA fuel cell

• Chemical analysis of Nafion• Membrane Electrode Assembly (MEA) consists of layers

microns thick• Thin Pt/C layers around a thicker Nafion layer

• Nafion is an effective proton exchange membrane• Permits hydrogen ion transport while preventing

electron conduction• Requirement to analyze profile of Pt in Nafion layer

• Layers are too thick for XPS sputter profiling• Not enough data points per layer with standard

cross-sectioning• Use ultra-low angle microtomy to create cross-

section with layers on micron scale2

• Enables XPS mapping and imaging analysis

2Journal of Materials Science 40 (2005) 285– 293

Backscatter image of cross-section of MEA fuel cell component

Anode

Cathode

Membrane

Data points

Backscatter image of ULAM-prepared MEA fuel cell component

Anode

Cathode

Membrane

Data points

Presenter

Presentation Notes

The MEA consists of layers which are tens of microns thick. An electron images of an MEA cross-section is shown on this slide. It shows the platinum-containing anode and cathode layers around the thicker Nafion electrolyte. The Nafion is electrically insulating but allows transport of hydrogen ions. These layers are too thick for conventional XPS depth profiling and so some kind of sectioning is required for XPS analysis. If we create simple 90 degree cross-section of the MEA, the probe size of a typical XPS tool will be too large compared to the layer dimensions to acquire more than a few data points across a given layer: it will not be possible to detect subtle diffusion of the platinum from one layer to another. A solution to this problem is to use ultra low angle microtomy (or ULAM). The MEA is then cross-sectioned at an angle of 1 or 2 degrees, allowing the analyst to obtain effective depth information by imaging the cross-section. The dimensions of the ULAM-sectioned layers are now large enough compared to the X-ray probe area that it is possible to have many data points per layer.

18

MEA fuel cell

Pt/C

Pt/C

Nafion

ULAM-prepared MEA fuel cell

Epoxy

Nafion

Chemical analysis of Nafion

MEA fuel cell

• Chemical analysis of Nafion• XPS can distinguish carbon bonding states

• Epoxy (used in making the ULAM cross-section)• C-C, C-O and C=O bonding observed

• Nafion (part of the MEA)• CF2 bonding observed• Surface contamination of Nafion gives additional C-C

and C-O peaks

Presenter

Presentation Notes

For XPS analysis, the ULAM section was mounted on expoy. XPS can distinguish between the carbon bonding states in Nafion and epoxy. Spectra from the epoxy and Nafion regions of the MEA ULAM sample are shown on this slide. The spectrum from the Nafion shows has a strong peak associated with CF2 groups in the polymer. It also has a lower energy peak associated with adventitious carbon contamination. The epoxy spectrum has components associated with aromatic and aliphatic carbon and also due to ether and carboxyl type bonding.

19

Element At%

Pt 0.41

S 0.44

C 73.68

O 10.08

F 15.39

Atomic concentration of elements in Pt/C layer

MEA fuel cell Elemental quantification of MEA-ULAM sample

Pt/C Nafion

ULAM-prepared MEA fuel cell

0.00

10.00

20.00

30.00

40.00

50.00

60.00

70.00

80.00

90.00

Pt (x50) S (x50) C O F

At%

Element

Nafion

Pt/C

Epoxy

Elemental quantification of MEA-ULAM sample

MEA fuel cell

• Elemental quantification of MEA-ULAM sample• XPS can elementally quantify small areas on a sample

• Quantification of Pt/C, Nafion and Epoxy zones below

• Fluorine observed in Pt/C zones• Nafion intentionally mixed with Pt/C during manufacture

of catalyst layer• Sulfur detected in all regions, principally in Nafion

and Pt/C zones• XPS is able to detect elements at low concentration

(S<0.5at% in Pt/C zone)• Pt detected in catalytically active layer

Presenter

Presentation Notes

XPS was used to quantify the elemental composition of the MEA-ULAM sample at different areas on the surface. The analysis areas are marked in the optical image and the quantification results are shown in the bar chart. Fluorine and sulfur were observed in the catalyst layer. These are expected since a small amount of Nafion was mixed into the platinum-carbon layer during manufacture, and Nafion itself contains a small amount of sulfur. Although sulfur is not a contaminant in the platinum layer, these results demonstrate the capability of the XPS tool to detect potential contaminants at low concentration. The concentration of platinum in the catalytically active layer is less than 0.5at% and so it is necessary to use a high performance XPS tool to detect it. This slide shows the platinum spectrum from the catalyst and Nafion layers. Even at low concentration, a high quality, good signal-to-noise spectrum was acquired from the catalyst layer. In middle of the Nafion layer, there was no detectable platinum.

20

MEA fuel cell Large area XPS mapping

MEA fuel cell

• Large area XPS mapping• Possible to quantify elements/chemical states over a wide

sample area• Map of Pt/C and Nafion zones shown below, overlaid on

optical image of MEA-ULAM sample• Linescan from map confirms no large scale diffusion of Pt

• 0% Pt in Nafion, in agreement with spectroscopic result on previous slide

Quantified Pt at% linescan taken from large area XPS map

Pt in catalytically active layers

No Pt in Nafion zone

Principal components phase map of MEA sample

Pt/C

Pt/C

Nafion

Large area XPS map of Pt / Nafion layers and interfaces in ULAM-MEA fuel cell sample

Pt/CPt/C Pt/CPt/CNafion

Linescan from mapping data

Presenter

Presentation Notes

We have seen elemental quantification from discrete areas on the MEA-ULAM sample, but it is also possible to use XPS to quantify elemental AND chemical states across a wide area of the sample. For example, a map of epoxy versus Nafion versus platinum is shown on this slide. This map was generated by acquiring full spectral datasets at each mapping pixel and using principal components analysis to automatically correlate the data. It is also possible to take the quantified mapping data and overlay it onto an optical image of the sample, or take a cross-section of the mapping data to generate an atomic concentration linescan. The linescan shows the atomic concentration of platinum along a line across the cathode, Nafion and anode layers, and it demonstrates that there is no large scale diffusion of the platinum into the Nafion.

21

Membrane Electrode Assembly

• Analyses performed at 10kV on a FESEM

Spectral Image net count maps

(background subtracted)

Nafion

Pt/C

22

Membrane Electrode Assembly

• Linescan analyses (50 points)

• No apparent migration from the Pt/C electrode into the Nafion

Si

C

PtF

Pt

Case Study 2: Thin film solar cell

24

Delaminated CIGS solar cell

3SEM of a Cu(In,Ga)Se2 solar cell (cross-section) and its mode of operation

• Energy/environmental application• Solar cells based on Cu(In, Ga)Se2 (CIGS)

• Thin-film stack on glass (or in this case steel)• Mo and Zn oxide layer form electrical contacts• p-type CIGS film (sunlight absorber) and n-type

CdS film form p-n junction• Excellent efficiency• Low cost compared to thicker silicon-based solar cells

• Practical problem• Delamination of device• Controlling film composition and interfacial chemistry

between layers (affects electrical properties)• Solution

• EDS imaging of good & delaminated areas

High resolution elemental information• XPS imaging & sputter depth profiling

Elemental and composition information as a function of depth

Identify delamination layer

3 D. Abou-Ras et al. Elemental distribution profiles across Cu(In,Ga)Se2 solar-cell absorbers acquired by various techniques. In: M. Luysberg, K. Tillmann, T. Weirich (Eds.), “EMC 2008”, Vol 1: Instrumentation and Methods, Proceedings of the 14th European Microscopy Congress 2008, Aachen, Germany, September 1-5, 2008 (Springer, 2008) p. 741.

Presenter

Presentation Notes

Solar cells based on (CIGS) thin films have demonstrated excellent efficiencies and offer a low-cost potential as compared with bulk-silicon-based solar cells, which are about 200 times thicker. CIGS solar cells consist of a thin-film stack on a substrate (typically glass) as shown in the SEM image to the left of the slide. The molybdenum layer and the zinc oxide layer form the electrical contacts. The p-type CIGS film acts as the sunlight absorber layer, with a thin n-type CdS layer forming a p-n junction. The most common manufacturing methods are simultaneous or sequential evaporation or sputtering of copper, indium, and gallium. Vaporised selenium reacts with the metals in order to establish the final film composition. One of the major challenges in producing these thin film solar cells is to control the film composition. Reproducibility of the required layer design in commercial volumes has proven to be problematic. This is critical as the electrical properties of the cell depend on the exact composition of the layers. XPS depth profiling can be used to determine both the composition through the device, and the interfacial chemistry.

25


Delamination zone

Some of the CIGS material had delaminated from the substrate. Measurements were taken from the three distinct areas of the sample:

(1 & 2) the top layers of the sample(3) the metallic surface electrical contact material(4) the underlying metallic substrate.

EDS Point Analysis

26

Delaminated CIGS solar cellEDS Point Analysis

27


Locations 1 and 2 on the film are the same material consisting of a majority of In and Se with a small amount of Cu and a small amount of Ga. Only small amounts of Zn, O, Cd and S are measured due to the thin nature ofthese layers.

Location 3 on the metallic contact layer is silver.

Location 4 where the film is removed shows the base Mo substrate that the layers are grown on.

EDS Point Analysis

28


1

34

XPS point analysis at the same locations as the EDS analysis

XPS Point Analysis

2

29

Delaminated CIGS solar cellXPS Elemental analysis

01002003004005006007008009001000110012001300

Cou

nts

/ s

Binding Energy (eV)Se

3d

Mo3

d

C1s

Ag3d

In3d

Sn3d

5O1s

Zn2p

3

Ga2

p3

Red spectrum is average of points 1 & 2

1 & 2

3

4

30

Area 1

1.80E+04

2.00E+04

2.20E+04

2.40E+04

2.60E+04

2.80E+04

3.00E+04

3.20E+04

3.40E+04

480482484486488490492494496498500

Coun

ts / s

Binding Energy (eV)

Sn3d Scan

Elem

ent

SnO

0.00E+00

2.00E+04

4.00E+04

6.00E+04

8.00E+04

1.00E+05

1.20E+05

1.40E+05

1.60E+05

1.80E+05

440442444446448450452454456458460Co

unts

/ s

Binding Energy (eV)

In3d Scan

Elem

ent

InO

x

1.00E+04

2.00E+04

3.00E+04

4.00E+04

5.00E+04

6.00E+04

526528530532534536538540542544

Coun

ts / s

Binding Energy (eV)

O1s Scan

Met

al o

xide

Met

al C

O3

3000

4000

5000

6000

7000

280282284286288290292294296298

Coun

ts / s

Binding Energy (eV)

C1s Scan

C-C

or C

-H carb

ide

carb

onat

e

Cl2

s (M

etal

ClO

4) Chemical state analysis suggests that points 1 & 2 are indium-tin-oxide (ITO)

XPS Chemical analysis

31

Area 3XPS Chemical analysis

2300

2400

2500

2600

2700

2800

2900

3000

158160162164166168170172174

Coun

ts / s

Binding Energy (eV)

S2p Scan

Elem

ent

orga

nic

SO

2

Met

al SM

etal

SO

3

Met

al S

O4

2.00E+03

4.00E+03

6.00E+03

8.00E+03

1.00E+04

1.20E+04

1.40E+04

280282284286288290292294296298Co

unts

/ s

Binding Energy (eV)

C1s Scan

C-C

or C

-H

carb

ide

carb

onat

e

Cl2

s (M

etal

ClO

4)

0.00E+00

2.00E+04

4.00E+04

6.00E+04

8.00E+04

1.00E+05

1.20E+05

1.40E+05

1.60E+05

362364366368370372374376378380

Coun

ts / s

Binding Energy (eV)

Ag3d Scan

Ele

men

tA

g2O

AgO

2300

2400

2500

2600

2700

2800

2900

192194196198200202204206208210

Coun

ts / s

Binding Energy (eV)

Cl2p Scan

Met

al C

lO4

Met

al C

l

1.00E+04

1.10E+04

1.20E+04

1.30E+04

1.40E+04

1.50E+04

526528530532534536538540542544

Coun

ts / s

Binding Energy (eV)

O1s Scan

Met

al o

xide

Met

al C

O3

32


EDS

XPS

Point analysis comparison

Ga-K Zn-K O-K Cr-K In-L Cd-L Ag-L Mo-L Se-K Fe-K Cu-K

Area 1 2.90 2.51 17.38 0.82 24.32 7.42 2.31 22.93 2.41 12.39Area 2 3.01 2.88 17.60 0.69 24.99 7.77 2.09 21.63 2.49 12.31Area 3 100.00

Area 4 17.66 61.00 2.92 18.42

Ga2p3 Zn2p3 O1s Sn3d5 In3d Ag3d Mo3d Se3d C1s S2p Cl2p

Area 1/2 0.16 52.41 2.49 33.39 0.03 0.22 0.32 10.99

Area 3 12.38 0.23 3.13 28.40 52.18 2.01 1.67

Area 4 0.97 0.37 19.47 0.00 1.99 23.95 24.77 28.47

EDS shows the presence of the expected stack components.XPS shows the presence of small contaminants, and the nature of the outer layer.

33

Delaminated CIGS solar cellXPS Mapping

34

Delaminated CIGS solar cellPhase 1 Phase 2 Phase 3 Phase 4 Phase 5

Se3d 1.55 32.21 2.60 0.99 3.85S2p 0.38 0.75 3.84 0.39 0.47Mo3d 0.62 26.94 1.11 0.15 2.48C1s 16.54 6.27 52.72 21.67 17.32Ag3d 0.16 0.27 12.91 0.08 0.25Cd3d 0.11 0.02 0.05 0.17 0.24In3d 27.99 4.56 4.66 25.21 25.41Sn3d5 2.74 0.50 0.58 2.48 2.49O1s A 36.63 20.47 5.46 33.62 34.67O1s B 11.81 6.85 15.77 13.09 11.29Zn2p3 1.45 0.31 0.26 2.11 1.44

Ga2p3 0.02 0.84 0.02 0.04 0.09

XPS Phase Analysis

35

CIGS solar cell Cross-section of CIGS film stack

Low MagnificationA Spectral Imaging mapping analysis was performed at low magnification on the cross-section sample to understand all of the layers that constitute the material. The thickness of all of the layers was approximately 1/3 mm.

Presenter

Presentation Notes

A sample of a CIGS solar cell was depth profiled using a Thermo Scientific XPS tool. Argon ions were used to profile the sample. The depth scale was been calibrated to a Ta2O5 standard sample. The calibration was checked using an SEM image of a cross-section of the sample. The sample was profiled using a rotating stage to give the best depth resolution through a very thick multilayer sample. The sample rotation was done off-axis (compucentric) which enables several profiles to be carried out on the same sample or separate without the need to remove them from the instrument. The depth profile on the left shows the structure of the solar cell. Firstly we see the upper ZnO layer and the Mo substrate. A change in stoichiometry of the ZnO layer as a function of depth was observed. Quantitative chemical information like this can be important in identifying causes for failures, for example.

36


Presenter

Presentation Notes

Further investigation concentrated on the outmost surface of the Iron layer at higher magnification. Elemental maps indicated layers of Cu, Ga, Se, Mo and In. The first Cu-Ga-Se layer had very low X-ray counts and the second layer was higher in In content. The low X-ray count layer seemed to be recessed in physical appearance indicating preferential polishing of this particular layer of the sample may have occurred. Because of the thin nature and common environment, this preferential polishing indicates a different hardness and could derive from a different composition than the following layer. The thickness of the Mo layer was just under 1 μm while the Cu-Ga-Se layers were just under 3 μm and 1.5 μm respectively. No CdS or ZnO phases were observed, probably due to their thin nature and the larger X-ray generation volume.

37


Presenter

Presentation Notes

A sample of a CIGS solar cell was depth profiled using a Thermo Scientific XPS tool. Argon ions were used to profile the sample. The depth scale was been calibrated to a Ta2O5 standard sample. The calibration was checked using an SEM image of a cross-section of the sample. The sample was profiled using a rotating stage to give the best depth resolution through a very thick multilayer sample. The sample rotation was done off-axis (compucentric) which enables several profiles to be carried out on the same sample or separate without the need to remove them from the instrument. The depth profile on the left shows the structure of the solar cell. Firstly we see the upper ZnO layer and the Mo substrate. A change in stoichiometry of the ZnO layer as a function of depth was observed. Quantitative chemical information like this can be important in identifying causes for failures, for example.

38

Delaminated CIGS solar cellXPS Depth Profile

3keV Ar+ ion beam60s etch timeCompucentric rotationDepth scale calibrated to EDS result

39

ZnO

CdS

CIGS Mo Cr SteelITO

0

10

20

30

40

50

60

70

80

90

100

0 1000 2000 3000 4000 5000 6000

Ato

mic

per

cent

(%)

Etch Depth (nm)

Se3dS2pMo3dC1sCd3d5In3d5Sn3d5O1s AO1s BCr2p3Fe2p3Cu2p3Zn2p3Ga2p3


40

0

10

20

30

40

50

60

70

80

90

100

0 1000 2000 3000 4000 5000 6000

Ato

mic

per

cent

(%)

Etch Depth (nm)

Se3dS2pMo3dC1sCd3d5In3d5Sn3d5O1s AO1s BCr2p3Fe2p3Cu2p3Zn2p3Ga2p3


0.00E+00

2.00E+03

4.00E+03

6.00E+03

8.00E+03

1.00E+04

1.20E+04

1.40E+04

438440442444446448450452454456

Coun

ts / s

Binding Energy (eV)

In3d

41

CIGS Mo Cr Steel


0

10

20

30

40

50

60

70

80

90

100

0 1000 2000 3000

Ato

mic

per

cent

(%)

Etch Depth (nm)

Se3dS2pMo3dC1sIn3d5O1s AO1s BCr2p3Fe2p3

42


ZnO

CdS

CIGS Mo Cr SteelITO

43


CIGS Mo Cr Steel

Presenter

Presentation Notes

Delamination at interface between CIGS & Mo layers (good match in thickness

44


Ga/In gradient

Delamination zone

Ag contact

Presenter

Presentation Notes

Delamination at interface between CIGS & Mo layers (good match in thickness

45

Acknowledgements

• Oak Ridge National Laboratory – (HTML)• RJ Lee Group• Application specialists in East Grinstead, UK & Madison, USA

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