8 y.veschetti ok

BIFACIAL CELLS

EXISTING TECHNOLOGIES &

REQUIREMENTS

Y. Veschetti

Mail : [email protected] CEA/INES-RDI, 50 Av. Du Lac Léman, 73377 Le Bourget du Lac, FranceBIFI WORKSHOP

2ND EDITION

CELL SESSION

bifi PV workshop 2014.05.26 Chambéry

VESCHETTI Yannick

OUTLINE

TRENDS IN PV CELLS TECHNOLOGY

BIFACIAL CELL TECHNOLOGIES

- State of the art: lab & industrial scale

- Process characteristics

- Material sensitivity

REQUIREMENTS FOR BIFACIAL APPLICATION

CONCLUSION

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VESCHETTI Yannick

Characteristics of the standard p-type industrial process

• Simple: Few fabrication steps, limited CAPEX• Most cell production lines are based on p-type standard technology• High experience from mass production• Continuous improvement in efficiency over the last years • Adapted to mono Cz and to mc-Si

3

A very competitive p-type process

p+ BSF & contact

ARC coating (SiN)

P-type substrate

N++ -emitter

Al contact

Wafer Eta (%)

mc-Si 17.5

Cz 19.0


VESCHETTI Yannick

P-TYPE PROCESS EVOLUTION

To keep improving the efficiency, the standard p-type technology will be more complex: --> end of Al-BSF

Development of PERC cell technology with additional process steps as:Al2O3, laser opening, advanced surface cleaning, …

Room for alternative technologies if cost/Wp remain competitive

International

Technology

Roadmap for

Photovoltaic

(ITRPV),

5th edition, March

2014, www.itrpv.net

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VESCHETTI Yannick

Courtesy of CEA-INES

Bifacial technologiesPERT technology

Passivated Emitter Rear Totaly Diffused

Courtesy of Sanyo-PANASONIC

Heterojonction technology

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IBC technologyInterdigitated Back Contact

Courtesy of ISC Konstanz


VESCHETTI Yannick

HIGH TEMPERATURE APPROACH : PERT *

• Mostly developed on n-type Cz Si

• Compatible with current production lines

• Efficiency improvement: From 18.5% in 2009 to

20.7% in 2014.

SiO2\SiN

Si(n)Phosphorous BSF

Boron Emitter

SiO2/SiN

Back grid

Front grid

PERT: Passivated Emitter Rear Totally diffused

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PERT Voc (mV) Jsc

(mA/cm²)

FF (%) Eta (%)

N-type Cz 650.0 39.0 79.0 20.0

Current PERT cell parameters


VESCHETTI Yannick

PERT CELL: STATE OF THE ART

7- R. Kopecek & J. Libal, PV International, Sep 2013- Proceedings of SiliconPV & nPV workshop 2014, ‘Hertogenbosch |

Company/ institute Country Technology Metallization Status Efficiency Module

ECN Netherlands Diffused

Screen-printing Laboratory 20.0 +/- 0.5

ISC Germany Diffused CEA-INES France Diffused, Implanted

Suniva USA ImplantedIrysolar France DiffusedISFH Germany Diffused

Motech Taiwan DiffusedApplied Mat USA Implanted

Tetrasun USA Diffused? Copper-plating Pilot-line 20.5-21.0 Bifacial

Bosch-Solar Germany Hybrid/implanted Screen-printing Pilot-line 20.5 ?

bsolar Israel/Germany Implanted?Screen-printing

Production

19.0 Bifacial

YINGLI China Diffused 19.5 Monofacial

PVGS Japan Diffused 19.5-20 Bifacial

LG Electronics Korea Implanted 20.5 - 21 Monofacial

• More and more academic and industrial actors• Different process technology• All actors on n-type Si except bsolar• Efficiency potential towards 21% using screen-printing


VESCHETTI Yannick

PROCESS SPECIFICITY

BORON DIFFUSION:

• High temperature required for B-diffusion: 900°C-1050°C• Potential impact on bulk lifetime• Limited experience in production• Existing solutions : Gas diffusion: BBr3 (Tempress, CT), BCl3 (SEMCO) Solid-source: SOD or APCVD/PECVD doped layers Implantation (ion implantation/plasma immersion)

B-emitter passivation:

• Thermal oxidation (dry or wet)• Al2O3 (ALD/PECVD)• Chemical oxide (NAOS)

Contacts:

• Ag/Al on B doped layer• Ag on P doped layer• Sensitive co-firing

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EFFICIENCY LIMITATION

B. Lim et al. | March 27, SiliconPV & nPV workshop 2014, ‘Hertogenbosch | 9

• Important gap between i-Voc (before metallization) and final cell Voc• Metal penetration into the diffused region and degrades the metal-Si

interface• B-emitter contact correspond to more than 40% of the entire cell J0.

A. Elder et al.Prog. Photovolt: Res. Appl. (2014)

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VESCHETTI Yannick

IMPACT OF MATERIAL QUALITY

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• Many studies showed thatefficiency remain stable overdifferent suppliers, ρ, positions• Eta: 19.9% - 20.4% fortaubulk: 500µs to 4ms

M. Forster, nPV workshop, Hertogenbosch 2014

• Process also compatiblefor alternatives materials- n-type Monolike Si: 19% [1]- mc-Si(n) EG: eta 16.2% [2]

Cz cells

Fraction available: 16% - 90%Average efficiency: 18.8%[1] Y. Veschetti et al. Proceedings PVSEC Paris, 2013

[2] T. Schutz-Kuchly et al. Prog. Photovolt: Res. Appl. 2013; 21:1214–1221


VESCHETTI Yannick

a-Si:H/c-Si heterojunction

One producer: SANYO-PANASONIC

• Efficiency > 21% in production• Record lab 24.7% sur 100 cm²

Source Sanyo Characteristics:

Difference in bandgap between a-Si and c-Si leads to an excellent surface passivation high Voc

Low Temperature process, ca. 200 °C

Excellent T coefficient Pmax (-0.3%/°C)

Compatible for thin substrates

Accurate process but limited number of steps

Efficiency potential in production > 22%

Not much compatible with existing lines11

HET CELL - STATE OF THE ART (R&D)

050

100150200250300350400450

USA+Canada

Europe

Japan

Rest of Asia

*Analyse from Scopus database

WR

21,5%

WR

23,7%

WR

20,1%WR

18,1%

WR

24,7%

Publications /year on « Silicon heterojunction solar cells »

• Japan leader in HET• Europe strong

expertise and many institutes involved

• Asia growing interest

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Institute/company JSC (mA/cm²) VOC (mV) FF (%) Efficiency (%) area (cm²)

Panasonic 39.5 750 83.2 24.7 100Kaneka 40.0 738 81.9 24.2 171Choshu 37.3 733 81.8 22.3 240

R&R 38.1 734 79.9 22.3 240EPFL 39.1 728 78.6 22.4 4

CEA – INES 38.7 730 78.8 22.3 105AUO 37.5 724 81.9 22.3 240

P-J. Ribeyron et al. nPV workshop, Hertogenbosch 2014

STATE OF THE ART AT THE PILOT LINE/INDUSTRIAL LEVEL

• Several pilot lines running• BUT only one player at the

industrial level• Best cell efficiencies

reported > 22%• Mean efficiency ???

USA

KOREA

JAPAN900 MW

CHINAX pilot lines

EUROPE

• Difficulties to compete against mainstream technology • Hard times from 2011 due to PV crisis oversupply and price drop

• Since 2009: Growing interest at the industrial level

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http://www.oynot.com/files/images/world-insolation-map-04-1250x691.gif

Higher sensitivity of the Wafer quality on the HET efficiency Voc is the leading parameter for HET

More than 1 % efficiency difference for the same cell process FlowStrong effect of Interstitial oxygen content and related defect distributionEffect of thermal donors to be adressed

IMPACT OF MATERIAL QUALITY

P-J. Ribeyron et al. nPV workshop, Hertogenbosch 2014

Results on INES

HET pilot line

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VESCHETTI Yannick

Bifaciality measurement

Bifaciality factor = Rear efficiency over Front efficiency

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Technology PERT

(Cz)

HET

BF (%) 87 – 95% 90 – 95%

0

20

40

60

80

100

300 500 700 900 1100

Wavelength (nm)

Inte

rnal Q

uan

tum

eff

icie

ncy (

%)

Front sideRear side

BF will depend on:• Bulk lifetime• Rear side passivation• Grid density at the back

PERT cellBF = 92%

Ref Mesure Voc (mV) Jsc

(mA/cm²)

FF(%) Eta (%)

CEA* Conductive chuck 639.5 39.1 79.5 19.9Bifacial mode 639.1 38.6 79.0 19.5

ISFH* Conductive chuck 658.0 38.6 80.0 20.3Bifacial mode 657.0 38.2 79.5 20.0

* Independently measured at ISE CalLab

Measurement methods


VESCHETTI Yannick

REQUIREMENTS IN

BIFACIAL CONFIGURATION

No conductive/reflective chuck

Illumination at the front and at the back

Increase of current in the cell 5 (up to 15A for 6 ‘’ cell) Additional resistive losses The cell will not be optimized Need to consider Vbd

A I-V measurement system with

simultaneous front & back illumination

Is necessary

Alternative:

If back Jsc ≈ front Jsc Evaluate resistive losses with higher front illumination (1.5 Sun)

0 to 1000 W/m²

0 to x W/m²

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CONCLUSION

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Remaining challenges:

• Cell efficiency is not enough should be confirmed at module level• Cell processing cost should not be too far from std technology Process simplicity, low consumables, high efficiency, …• Process qualification is necessary (Stability, low illumination, Vbd, …)• Cost of n-type wafer (+15% versus p-type) and access to high quality Alternatives material: mc-Si /monolike Si• Need more data on cell performances in bifacial configuration

Two technologies well suited for bifacial application

More & more actors, starting of pilot-lines, production lines

Technology Front eta Process

simplicity

Material

compatibily

Line

compatibility

T° coef

PERT + - ++ + -HET ++ + - - +

Commissariat à l’énergie atomique et aux énergies alternativesINES RDI | Savoie Technolac – BP332 – 50 avenue du Lac Léman73377 Le Bourget-du-LacT. +33 (0)4 79 79 29 38 Email : [email protected]

Etablissement public à caractère industriel et commercial | RCS Paris B 775 685 019

Direction de la Recherche TechnologiqueLaboratoire d’innovation pour les technologies des énergies nouvelles et les nanomatériauxDépartement des Technologies SolairesLaboratoire des Matériaux et Procédé pour le Solaire

Thank You!

Presentations & Public Speaking

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