SUPSI Industry Day 2019Overview on LeTID phenomenon and Industry Solutions to manage it

Andrea Viaro | Head of Technical Service Europe, JinkoSolar | 08.11.2019

http://www.jinkosolar.com/http://www.jinkosolar.com/

Mechanism postulate 1: Metal-Induced Degradation

2

MID – Metal Induced Degradation:Metal Ions in silicon gather at the grain borders to form stable defects acting as recombination centers

Jinko Solution: Reduce the ratio of Metal Ion impurity in mono-crystal ingotsby optimizing production process and parameters

Source: Mallory A. Jensen， MIT，IEEE JOURNAL OF PHOTOVOLTAICS, 2018

Source: Klaus Ramspeck，27th European Photovoltaic Solar Energy Conference and Exhibition，861-865

Mechanism postulate 2: Hydrogen-Induced Degradation

3

Fermi Energy Level

HID – Hydrogen Induced Degradation:Hydrogen Atoms diffuse into the silicon and combine with positive ions into more stable state, which reduces the PV cell activity

Jinko Solution: Optimal Hydrogen content and fine-tuning of equipment employed in mass production (also in cooperation with external R&D centers e.g. UNSW)

Source: Alison Ciesla née Wenham, Hydrogen-Induced Degradation, UNSW, 7th world conference on photovoltaic energyconversion, P1-8, 2018.

Mechanism Study: Mono VS Poly

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Poly PERC Mono PERCMID Higher content of metal

impurities→higher MIDLower content of metal impurities→lower MID

HID Same effect on poly and mono, relative to cell process

Source: Daniel Macdonald, AIST, JOURNAL OF APPLIED PHYSICS 97, 033523 2005

Source: E. Garcia Goma, Eternal Sun Group and UNSW, 35th European Photovoltaic Solar Energy Conference and Exhibition,

Brussels, Belgium 2018

LeTID mitigation: Possible Strategies

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Solution Technology: Advanced Recipe

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Crystal Growing

Slicing wafer

Mono PERC Cell

Module

Process fields Controlling Technology

Impurities Controlling Technology

LIR Technology

Decrease the content of Metal Impurities

and Oxygen

Decrease the content of impurities and

defect in stable level

Control the Hydrogen content to reduce LID

(insufficient H) and LeTID (excessive H)

Solution Technology: Monocrystal Pulling Control Tech.

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The technology developed by Jinko R&D can reduce Metal and Oxygen atoms by optimizing the different process phases parameters

Stress field

Thermal field

Magnetic field

Velocity

Flow

Concentration

7

Solution Technology: Impurities Controlling & LIR tech.

8

Texturing

High resistance diffusion

Passivation Layer

ARC coating

Laser

Metallization

LIR Light-Induced Regeneration

Design specific process parameters (e.g. Temp.) to:

1. Remove effectively impurities from the surface

2. Reduce metal impurities diffusion into the silicon

3. Decrease probability of forming stable defects

4. Reduce energy consumption and CO2 emission

1. Optimize Hydrogen content to Control both

• LID caused by insufficient hydrogen

• LeTID caused by excessive hydrogen

2. LIR single-cell, in-line stabilization is more

effectively in mass production, compared to CIR

stacked-batch processing

Light Induced Regeneration (LIR)

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• Illumination of mono cz. P-type solar cells Eff. reduction up to 5% abs

• Main cause: recombination of active Boron–Oxygen complexes (B-O),

especially in highly Boron-doped & Oxygen-rich silicon

• Light-induced Hydrogen Passivation (LiHP) can dramatically reduce LID,

i.e. improve regeneration process

• Key parameters to deactivate Boron–Oxygen complex (Passivation):

Temperature, carrier injection, Hydrogen diffusion

Mass Production Control: long-term test of samples

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300 kWh LeTID test result on Mono PERC Modules

After 60Kwh regeneration starts

0.90%

1.03%

0.0%

0.2%

0.4%

0.6%

0.8%

1.0%

1.2%

1.4%

10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160 170 180 190 200 220 240 250 270 280 300

60Kwh

Testing temperature：75±5℃（surface）Light source：1Kw(steady)

Pow

er D

egra

datio

n

Mono PERC Sample No.1Mono PERC Sample No.2

Mass Production Control: third-party test result

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LeTID test at 75±5℃ with CID procedure Result from mass production (average -0.6% Pmpp) Jinko Mono Perc Modules (2018)

Current： 9.9A（Imp）Test Period: 162h

Chart1

Sample.1

Sample.2

Sample.3

Sample.4

Sample.5

Sample.6

系列 1

Power Degradation Ratio

0.006

0.008

0.004

0.007

0.006

0.007

Sheet1

系列 1

Sample.10.60%

Sample.20.80%

Sample.30.40%

Sample.40.70%

Sample.50.60%

Sample.60.70%

Mass Production Control: sampling data

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60Kwh LeTID test result of Mono Perc Modules (throughout 2018) LID test 1kW (steady) with Temperature raised to 75±5℃ Simulating extreme environment → Similar to LeTID

0.85%

0.97% 1.00%

1.12%1.20% 1.17%

1.03% 0.99% 0.99% 0.98%1.05%

0.00%

0.20%

0.40%

0.60%

0.80%

1.00%

1.20%

1.40%

2018-1 2018-2 2018-3 2018-4 2018-5 2018-6 2018-7 2018-8 2018-9 2018-10 2018-11

Conclusions: management control integration

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Advantage of complete value-chain

vertical integration

Manufacturer efforts in L(eT)ID reductionenable to effectively reduces risk in PV investments

IEC Standard ,under development, will give an accurate approach to evaluate the phenomenon

Ingot purity, wafer processing and cell stabilization are key to control L(eT)ID effect in mass-production

PV cell and module regeneration strictly dependon temperature and light/current intensity

High silicon quality and optimized manufacturing lead to reliable PV modules

Thank You!

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