x-ray based techniques for microanalysis of solar cells ... module lifetime... · x-ray based...

X-ray based techniques formicroanalysis of solar cells

and modulesMichael Toney, Synchrotron Materials Sciences Division

Piero Pianetta, Deputy DirectorStanford Synchrotron Radiation Lightsource (SSRL)

SLAC National Accelerator Laboratory


• ~1,700 employees + 3,400 users, visitingscientists per year; 300 postdocs andstudents; 75 PhD theses

• Major DOE-BES scientific user facilities:o Linac Coherent Light Source (LCLS)o Stanford Synchrotron Radiation

Lightsource (SSRL)• Science Programs:o Particle Physics & Astrophysicso Accelerator Researcho Photon Sciences

Chemical and Materials SciencesSustainable Energy Materials

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Stanford3 km


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SSRL

LCLS-offices

Few other labs in the world currently hosts such a unique andcomprehensive suite of x-ray sources and instrumentation

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1. SLAC today2. SSRL work in PV

Ag-Si contact (gridline) formation3. Si degradation modes & X-ray microanalysis4. Degradation cause microanalysis - post mortem

microscopy & spectro-microscopy – full field, scanning• initiation sites (cracks, PID, Metallization)scattering• EVA degradation

5. Degradation - operandodiffraction (HOIP)

6. Summary

Outline

SSRL PV Experience

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SSRL MSD PV research: processing – structure - functionThin Film

• CZTSSe and doped CZTSSe – atomic structure• CIGS processing – routes to form CIGS

Emerging• Hybrid perovskite absorbers (CH3NH3PbI3)• Organic PV• Novel TCOs

Silicon• Ag-Si contacts rapid thermal processing

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Ag-Si contact (gridline) formation

• Ag contacts (gridlines) made onSiN anti-reflection coating

• Ag paste Compositiono ~90% Ag particleso ~10% glass frit (PbO, …)o organic binder

• Frit allows SiN burn-through• Complex reaction

Uncertainty regarding key mechanisms

Ahmad et al. RSI, (2015).

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Front contact metallization of Si solar cells

In-situ diffraction during RTP• PbO (in frit) oxidizes/etches SiN (<600C)• AgO oxidizes & etches Si (600-800C)• Ag precipitates onto Si Fields et al., in preparation

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Outline





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Si Cell Degradation and Diagnostic Tools

• Cracksstrain - topography (Klaus)initiation sites – microscopy

• Metallization (snail trails, PID)initiation sites – microscopy

• Burn markssolder failures – microscopy

• encapsulant (EVA) degradation & embrittlementpolymer morphology – small angle scattering

microanalysis ofdegradationinitiation sites &propagation

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Multi-modal Diagnostic Tools

0.1 nm 1 nm 10 nm 100 nm 1 µm 10 µm

atomicbonding

Grain size

Cell level

Probed Length Scale

X-rayMicroscopy (XM)

X-ray diffraction (XRD)X-ray Absorption Spectroscopy (XAS)

small angle X-rayscattering (SAXS)

cracks, metallization: XMEVA: SAXS

many techniques (length scales, modalities)

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Multi-modal Diagnostic Tools - XASX-ray Absorption Spectroscopy (XAS)

• Every element absorbs X-rays well at a specific energy

• Regions around this energygive information aboutchemistry & local structure

• 3d transition metals

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Multi-modal Diagnostic Tools - TXM

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Capabilities:• Morphology – 30 nm resolution• 30 µm field of view – 100s µm (tiles)• 2D & 3D imaging (density, porosity)• Elemental/chemical maps• ca 5-14 keV

Phase ring

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Each pixel is an absorption spectrum

x [ m]

y[

m]

Nor

mal

ized

Gra

ysca

leIn

tens

ity

30 nm chemical resolution

NiO Ni (2+)

Ni

Liu, et al., J Synchr Rad (2012)Weker & Toney, Adv Func Maters. (2015)

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LiCoO cathode for Li ion batteries:• deep discharge

Wise, Weker, Toney, unpublished

local chemistry:• metal inclusions

(silicides)• 3D

Transmission X-ray Microscopy – CZTSSe film

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CuZnSnSSe film (Scarpulla, Utah)• co-sputtered; 15 min anneal - 500C• EDX: Cu(23)Sn(12)Zn(12)Se/S(53)• Film mounted FIB-SEM• Tomography :o Se: 4450 & 4515 eVo Cu: 8960 & 9030 eVo Zn 9640 & 9710 eVo Sn 12640 & 12710 eV

Pt mount

CZTSSefilm

Imagedregion

Pruzan, Scarpulla, Liu, Toney, unpublished

TXM – CZTSe phase localization

17Phase map (30 nm)

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Diagnostic Tools - TXM with phase contrast

Absorption contrast Phase contrast Andrews et al., Microsc Res Tech., (2011)

Au nanoparticles

cell

Phase rings:5.4 & 8 keV

Capabilities:• low contrast• see cracks• correlate with impurity

clusters or ???

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Ag

Si

W Tip

Ag Frit

Si substrate

image of FIBed Si cell

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Multi-modal Diagnostic Tools - STXM

Capabilities:• 20 nm resolution• thin (few microns)• 500 eV - 1000 eV• 2D element & chemical

maps• better sensitivity than

TXM

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APS nanoprobe

Capabilities:• 30 nm resolution• 6 keV – 12 keV• Elemental/chemical maps• Likely more sensitive than TXM

Bertoni et al,EES (2011)

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Multi-modal Diagnostic Tools - XM

In Depth Materials Microanalysis:• X-ray based microscopies – (30 nm - > 100s microns)• 3D element & chemical maps through wafer (tomography)

• assess crack initiation causes• manufacturing defects: metals, other impurities• causes of crack propagation

• down select from topography, EL, PL, Raman, …• down select to TEM

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Outline



microscopy & spectro-microscopy – full field, scanning• initiation sites (cracks, PID, Metallization)scattering• encapsulant (EVA) degradation


Small Angle X-ray Scattering (SAXS)

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• Q 0.001 – 1 Å-1

• inhomogeneities - 1-100 nm• polymer morphology

|Q| = (4 )sin

kincidentscattered

k’Q

V

3riQ212 rde||

V1I(Q) nn

small inhomogeneitybig inhomogeneity

EVA degradation & embrittlement - SAXS

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Ma et al., European Polymer J (2012)

existing & developed voids in EVA

Qy

Qx

• couple with UV/Visspectroscopies, FTIR• surface? – giSAXS(top 5 nm)

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Outline





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Degradation – operando XRD

CH3NH3PbI3 bias stability

Ungar et al., EES (2015)

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Degradation – operando XRD of CH3NH3PbI3

CH3NH3PbI3 bias stability

Summary

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• Cracks• Metallization (snail trails, PID)• Burn marks• encapsulant (EVA) degradation & embrittlement

Unique Toolset for microanalysis:• degradation initiation sites• causes of propagation

Degradation - operandoobserve failure events

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Thanks

SSRL Staff• Chris Tassone• Kevin Stone• Hongping Yan

x-ray based techniques for microanalysis of solar cells ... module lifetime... · x-ray based...

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