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
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
SLAC National Accelerator Laboratory
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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
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)
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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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Multi-modal Diagnostic Tools - TXM
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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Multi-modal Diagnostic Tools - TXM
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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Multi-modal Diagnostic Tools - TXM
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
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• encapsulant (EVA) degradation
5. Degradation - operandodiffraction (HOIP)
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
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)
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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
