Outdoor test-site PI Berlin · PI Berlin: PV Module testing and R&D services Testing equipment Class A Flasher for STC precision measurements + weak light performance 3 climate chambers

Quality requirements for wafers, cells and PV modules

Stefan Krauter, Paul Grunow, Sven LehmannPI Photovoltaik-Institut Berlin AGPhotovoltaic Module TechnologyTesting | Consulting | Research

Intersolar 2008 in Munich, 12th of June 2008

Out

door

test

-site

PI B

erlin

cells & wafersabout PI Berlin modules thin film modules

Independent module testing lab (accreditation acc. to ISO 17025 in Q4 2008) Consulting R&D service provider in PV module technology

Thin filmstart-ups &

manufacturers

PV utilityinstallers

Moduleproducers

Cellproducers

Productdevelopers/Investors

PV retailers

PI Berlin Customers


PI Berlin: PV Module testing and R&D services

Testing equipment Class A Flasher for STC precision measurements + weak light performance 3 climate chambers 2.8m x 3.0m x 2.6m (damp-heat, thermal cycling, humidity-freeze) Steady state simulator class B (STC for thin film modules, hot spot, light soaking) Outdoor test-site: NOCT, yield comparison, max. 40 modules UV chamber, area: 2.0m x 3.6m x 2.0m Wet leakage electrical isolation test (up to 6000 V) Mechanical tests (load, hail, rip-off) Accelerated TCO corrosion tests EVA gel content test

Equipment for Research and Development Module lamination service:

Edge delete, contacting, lamination IR-thermography, Electroluminescence Spectral response measurement Fig.1: Outdoor test site in Berlin

4 founders in October 2006, 20 employees in June 2008


Characterisation in PV manufacturing

• Yield improvement = average efficiency x mechanical yield

• Continuous throughput increase• Raw material supplier feed-back• Safety & reliability and energy yield check (module)

Prominent example:

Expected benefits:

• Cell or module binning in power classes ->mismatch reduction in the module or in the system

e.g. Field&Gabor 29th IEEE PVSC, New Orleans 2002, p. 418


Which characterisation tools make it from the laboratory into the production?

• Fast: ≈ 1s • Reliable and easy to interpret• Relevance of revealed parameters• Invest vs. potential yield improvements

Investment and its return for the prominent example:

Needs:

• Cell sorting in 0.2% steps for cells between 14%-17% with a sorter at 3% of total invest*→ ≈ + 3% in average module power**

*=0.3 Mio € for a 30MW/a cell +module, ** = +2 Mio €/a -> i.e. already 0.1% yield improvement pays off the same invest


Wafer production

Crystallization

Ingot cutting

Wafer cutting

Sorting

poly-Silicon

Wafer

Cleaning

μ-PCD life timeIR spectroscopy

Visual inspection,balance: dimensions,mechanical defects

Resistivity, e.g.eddy current

No electronic quality check,no micro-crack inspectionat the final product!

Resistivity, e.g.eddy current

Silicon specification:Impurity contentsOxygen/carbon contents


Cell production

Wet etch

Diffusion

Wet deoxidation& edge isolation

Screen printing

wafer

SiNix ARC

Sheet resistivity

I-V curve: Iop@Vop*Pmax, Isc, Voc, FF,

Rseries, Rshunt

Visual:mechanical defects,

dimensions

Visual:colour

Firing

Sorting cell

Visual

Wafer specification:ResistivityDopantDimensions, geometryMechanical defectsImpurity/oxygen contentMinimum carrier life time

Feedback to wafer supplier:Electronic qualityMechanical quality


*Vop= 0.5 V as sorting criteria

New fast characterization of single wafers

Photoluminescence Imaging using a self-consistent calibration method as introducedby T. Trupke et al., Applied Physics Letter, Vol 87, 184 (2005)

-> Cell efficiency prediction on the wafer level in terms of the cell‘s potential Isc,To do for as-cut wafers: Measurement in HF or iodine solution, corona charging??


The et al. 22nd EPVSEC 2007, Milan, p. 354

Photoluminescence Imaging of raw wafers

BruchrisikoIn-Line Messungen Elektrolumineszenz Photolumineszenz

-> without passivation (such as cut):out-sorting of (EFG) wafers with low minority carrier lifetime possible

Trupke et al. 22nd EPVSEC 2007, Milan, p. 22

Micro crack inspection of wafers

Trupke et al. 22nd EPVSEC 2007, Milan, p. 22

Photoluminescence ImagingHistory of luminescence Imaging:

2005: T. Fuyuki, et al., Applied Physics Letters 86 (26) (2005) p. 262108

2007: >20 papers at the 22nd PVSEC in Milano related to electro- and photo-luminescence on wafers, cells and modules

Remark: older papers exists about photo emission microscopy (PEM) for failure analysis in microelectronics


Electroluminescence on finished cells (modules)


Finger interruptionscracks

Vacuum suction cups (zoom) Firing furnace belt(zoom)

local shunts(artificial, by wire connect back to front)

Hot spot risk test on cells

after D. Schüren from Sunware, private communication 2005* = cycle time

Infrared Imaging at -10V

W. Herrmann et al. 17th EPVSEC, Munich, 2001

Test criteria: Maximum temperature after 1s* < Tcritical


Cell production+

Wet etching

Diffusion

Wet de-oxidation & edge isolation

Screen printing

wafer

SiNx ARC

Sheet resistivity

I-V curve: Iop@Vop

Pmax, Isc, Voc, FF,Rseries, Rshunt

Visual check:mechanical defects,

dimensions

Visual check:colour

Firing

Sorting

EL camera • Finger interruptions,• Homogeneity,• Micro-cracks,• Local shunts

IR camera Hot spots

PL cameraFeedback to wafer supplier:Electronic qualityMechanical quality

cell

Visual check


Wafer specifications:• Resistivity• Dopant• Dimensions, geometry• Mechanical defects• Impurity/oxygen content• Minimum carrier life time

PL

PL

PL

PL

PL

Micro-crack alarm-system along the entire production process& software tool for visualisation of micro-crack attraction points

Module production

String soldering

Matrix soldering

Lamination

Sun Simulator test

Cell

Module

J-box & Framing

String testerPmax, Rseries

I-V-curve: Pmax, Isc, Voc, FF,

Rseries, Rshunt

EL camera

PL cameraFeedback to cell supplier:Electronic qualityMechanical quality

EL camera Stringer check

EL camera Check before laminationCell specification:• I@Vop• Pmax• Dimensions, geometry• Mechanical defects

low light I-V-curve: Pmax at 100-400 W/m2

Energy yield issue


Final check

Elektroluminescence on finished modules

- Local shunts- Finger

interruptions

- areas with low diffusion length

-Micro cracks


Thin Film module production

Deposition & Patterning

Edge deletion

Contacting

Sun Simulator test

Glass

TF Module / Laminate

J-box (& Framing)I-V-curve:

Pmax, Isc, Voc, FF,Rseries, Rshunt

Lamination

Visual: Laserpattern alignment

Insulation test

EL/PL camera

EL camera

Insulation test Safety issue

low light I-V-curve:Pmax at 100-400 W/m2

Energy yield issue

Voc check


Electroluminescence on thin film modules

CIGS: with several local defects/shuntsa-Si/μ-Si

-> fast detection/imaging of local material defects or processing faults

CdTe

local shunt

local shunt

badedgedelete


Yield of module prediction via operation model

Standard Test Conditions (STC)PV module power output at 25°C1,000 W/m2, AM 1.5g, normal incidenceTypical measurement duration: 4-10 ms

Real world is non-STC!Indoor test ≠ outdoor performance• Non-perpendicular incidence• Low irradiance levels• Spectral effects• Temperature effects • Degradation and regeneration

Electrical energy yield (kWh/a kWp)is predictable for crystalline technologies,but more difficult for thin film technologies(degradation, change of parameters)

Conclusions

• 0.1% yield improvement justifies an invest of 0.3 Mio€ in a 30 MW combined c-Si cell&module line at today’s pricings

• Electro- and photoluminescence are powerful tools for fast in-line imaging of electronic and mechanical properties on wafers, cells and modules, minimum yield improvement: 1%

• Hereby, the highest benefit is expected for micro crack detection, especially for highly automated production lines

• Since CCD cameras are used, they can be combined with/ or replace conventional visual inspection stations

• Safety risks (i.e., hot spot and isolation) and energy yieldpotential of the finished modules are important product properties in the field and should to be covered with similar investment efforts (recommended product strategy)

• Hall B6, 410

[email protected]@pi-berlin.comVielen Dank

Documents

Outdoor test-site PI Berlin · PI Berlin: PV Module testing and R&D services Testing equipment Class A Flasher for STC precision measurements + weak light performance 3 climate chambers