WS 2012 T13 Frankfurt 04 Kajari-Schroeder

IEA INTERNATIONAL ENERGY AGENCY

PHOTOVOLTAIC POWER SYSTEMS PROGRAMME

Crack statistic of

crystalline silicon

photovoltaic modules

S. Kajari-Schrder, I. Kunze,

F. Haase, M. Kntges

Institute for Solar Energy

Research Hamelin



Inactive cell area

Why analyze cracking of cells? Cell cracks in PV modules can lead

to electrically separated cell area

fractions after artificial aging

For 230W module with 60 cells: separated cell area fraction of 8%

or more leads to significant

reduction of module power

M. Kntges, I. Kunze, S. Kajari-Schrder, X. Breitenmoser, B. Bjrneklett, Sol.

Energy Mater. Sol. Cells (2011), doi:10.1016/j.solmat.2010.10.034

200 Humidity-

freeze cycles



Crack classification

no crack dendritic several

directions +45 -45

parallel

to busbar

perpend.

to busbar



Crack statistics Different load histories

Transport



Experimental as delivered 103 PV modules 60 cells

(15.6 cm), multicrystalline

From various manufacturers

Max. 5 PV modules/package

Inflict cracks to cells in PV module only by production or

transport

Determine local crack distribution in EL image

Production

Transport

EL

Exemplary image, not analyzed

transport

M. Kntges, S. Kajari-Schrder, I. Kunze, U. Jahn,

Proc. 26th EUPVSEC (WIP, Hamburg, Germany, 2011) 4EO.3.6



Lateral crack distribution As delivered

High breakage rate in center Moderate breakage rate

near frame

Low breakage rate in corners

Symmetry to increase statistical significance



As delivered

Lateral crack distribution

High breakage rate in center Moderate breakage rate

near frame

Low breakage rate in corners

Symmetry to increase statistical significance



PV modules show non-homogeneous crack distribution Distribution correlates with strain distribution of 1st eigenmode 45crack in corners does not correlate Tensile strain promotes crack growth

Noise reduction utilizing symmetries


Dendritic




Field



Measurement in the field 574 PV modules (multi cryst.) with FL method

M. Kntges, S. Kajari-Schrder, I. Kunze, SOPHIA Workshop PV Module

Reliability, May 4-3 2012, Lago di Lugano (Switzerland)

Exemplary image, not

the analyzed field

4CO.11.4

Exemplary image, not analyzed field




PV modules show non-homogeneous crack distribution Distribution correlates with strain distribution of 1st eigenmode Tensile strain promotes crack growth Parallel to busbar more often than tensile strain suggests

Dendritic





Uniform mechanical load



Uniform mechanical load

27 PV modules 60 cells (15.6 cm)

Multi & mono crystalline cells

From various manufacturers

Inflict cracks to cells in PV module by mechanical load test 5400 Pa

Determine crack distribution in EL image analysis

Flash/EL

Mechanical

load test 5400 Pa

Flash/EL

S. Kajari-Schrder, I. Kunze, U. Eitner, M. Kntges, Sol. Energy Mater. Sol. Cells

(2011),doi: 10.1016/j.solmat.2011.06.032




PV modules show non homogenous crack distribution Distribution correlates with strain distribution of load simulation 45 crack in corners is higher than expected Tensile strain promotes crack growth

Cracked cells [%] Dentritic cracks [%] Serveral directions [%]

R/C 1 2 3 4 5 R/C 1 2 3 4 5 R/C 1 2 3 4 5Cells per module: 60

1 59 37 44 38 36 1 5 1 2 2 3 1 6 2 3 3 1Number of modules: 27

2 27 52 53 46 46 2 9 9 6 6 10 2 5 9 10 4 1Cracked cells per module[%]: 41,2

3 31 31 40 35 43 3 11 4 8 6 10 3 8 6 14 6 11Cracked cells per module[#]: 24,7

Parallel to Busbar [%] Perpendicular to Busbar [%] 45 cracks [%] Simulation pressure 5400 Pa

R/C 1 2 3 4 5 R/C 1 2 3 4 5 R/C 1 2 3 4 5

1 0 19 35 32 32 1 0 0 0 0 0 1 48 15 4 0 0

2 1 18 30 33 33 2 1 0 0 0 0 2 10 16 6 3 1

3 4 12 15 22 21 3 6 0 0 0 0 3 1 5 11 1 0

R/C 1 2 3 4 5

1

2

3

Dendritic





Comparison



Different load histories compared

Transport Field Uniform mec. load

Busbars in: long direction short direction long direction Relative amount of cracked cells:

Transport: 5.74 %

Field: 4.15 %

Uniform: 41.2 %

Cracks are ubiquitous

Dendritic cracks more dominant in artificial

crack initiation

Cracks perpendicular to busbars are rare

Dendritic



Risk of cell part separation in

artificial aging



Separated cell area

Definition of the potentially

separated cell area:

Area that is limited by a crack or the

border of the cell and that has no

functional metal finger to the busbar

Different crack orientations have

different worst case separated cell

areas

different potential impact on module power output

Crack



Experimental

PV modules with 60 15.6x15.6 cm

mono & multi crystalline cells Power Measurement

Electroluminescence

Mechanical load test

(5400 Pa)

200 humidity freeze

cycles

Initiation of cracks into the cells in the PV modules with mechanical load test (IEC

61215)

Stressing of the cells by 200 humidity freeze cycles (similar to IEC 61215)

Power Measurement

Electroluminescence

Power Measurement

Electroluminescence



Potentially separated cell area all crack orientations

30 % of the cracked cells show less than 8 %

potentially separated cell

area

Low risk for power losses

11 % of the cracked cells show more than 25 %

potentially separated cell

area

High risk for power losses



Crack orientation dependence



Cracks parallel to the busbars shows peak between 16 24 % potentially separated cell area

Diagonally cracked cells mostly have lower potentially separated

cell areas

Crack orientation dependence



Experimental

PV modules with 60 15.6x15.6 cm

mono & multi crystalline cells Power Measurement

Electroluminescence

Mechanical load test

(5400 Pa)

200 humidity freeze

cycles

Initiation of cracks into the cells in the PV modules with mechanical load test (IEC

61215)

Stressing of the cells by 200 humidity freeze cycles (similar to IEC 61215)

Power Measurement

Electroluminescence

Power Measurement

Electroluminescence



Crack type definition EL Image @ Isc

EL Image @ 1/10 Isc

A A

A No resistance across crack

B B

B Degraded, still connected, but increased resistance

C C

C Isolated, inactive cell area



Isolated cell area after artificial aging

C

Correlation of potentially separated cell area due

to crack orientation and

electrically isolated cell

area after aging

7 % of the cracked cells develop isolated cell

parts

Isolated cell area of up to 17 %

iso

late

d



B



electrically degraded

cell area after aging

29 % of the cracked cells degrade in artificial

aging

Degraded cell areas of up to 34 %

Degraded cell area after artificial aging



B Cracks partially not

detected before aging



electrically degraded

cell area after aging

29 % of the cracked cells degrade in artificial

aging

Degraded cell areas of up to 34 %

Degraded cell area after artificial aging



Isolation and degradation of

different crack orientations

Relative probability for electrically isolated cell

area independent of crack

orientation

Cells with several crack orientations and cracks

parallel to the busbars

degrade most often



Summary Cracks are ubiquitous

Cracks distribution depends on load history

Cracks parallel to the busbars are most frequent and can separate large cell

areas

29 % of cracked cells degrade in aging

Funding was provided by the State of Lower Saxony and BMU under

contract number 0325194C TASK13



Advanced technologies and materials for

crystalline Si solar cells and modules

March 25 - 27, 2013 Hamelin, Germany

Scientific topics:

Junction formation Surface morphology and passivation Cleaning and etching Structuring and contact formation Silicon material Wafering and kerfless technologies Advanced characterization and simulation Process integration Module integration Reliability

www.siliconpv.com

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WS 2012 T13 Frankfurt 04 Kajari-Schroeder

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