advanced thin-film silicon solar cells · thin-film si solar cells on glass power plant roof...

Miro ZemanDelft University of Technology, The Netherlands

Acknowledgments:• Nuon Helianthos, OM&T, IPV Julich, Ljubljana University• SenterNovem for financial support

Advanced Thin-Film Silicon Solar Cells

Outline

Helianthos project

Status of thin-film Si solar cell technology

Issues for further improvement

Conclusions

Photon management

World of PhotovoltaicsPV industry: the fastest growing industry in the world

0

1000

2000

3000

4000

5000

1999 2000 2001 2002 2003 2004 2005 2006 2007

202 287 401560 750

1256

1815

~3800

MW Solar cell production 1999-2007

42% 40% 39% 34%68%

45%

50%

Photon International, March 2007

2006: 90% wafer-type c-Si technology

Estimation market:

2007Cumulative installed capacity of PV systems

~ 9200 MW

Turnover (modules+BOS)

~ 15x109 €~ 70 000 jobs

2536

40%

World of PhotovoltaicsPV industry: announced increase in capacity

0,0

5.000,0

10.000,0

15.000,0

20.000,0

25.000,0

30.000,0

35.000,0

40.000,0

45.000,0Pr

oduc

tion

Cap

acity

[MW

]

2006 2007 2008 2009 2010 2012

Crystalline SiliconThin Films

Arnulf Jäger-Waldau, EU-PVSEC-23, Valencia, 2008

World of PhotovoltaicsPV industry: announced increase in capacity

0

2.000

4.000

6.000

8.000

10.000

12.000

[MW

]

2006 2007 2008 2009 2010 2012

silicon basedCdTeCISDye + others

Oerlikon

Applied Materials

Arnulf Jäger-Waldau, EU-PVSEC-23, Valencia, 2008

Strategic Research Agenda: EU roadmap

www.eupvplatform.org

Wim Sinke (ECN, Leader of WG 3 : Science, technology & applications of EU PV Technology Platform)

Current developments:• Increase in TF Si solar-cell production (in 2010 ~ 8 GW capacity)• Complete production lines available

Future developments:• Short term: optimize tandem cell• Long term: optimize triple cell, breakthrough concepts for high

efficiency (η>17%)

Thin-film Si solar cell technologyPresent status:+ Promising low-cost solar cell technology+ Industrial production experience (Flat panel display industry)- Relatively low stabilized efficiencies (η ≈6-7%)+ Double-junction micromorph solar cell (η>10%)

• ideal combination of materials (a-Si:H/μc-Si:H) for converting AM1.5 solar spectrum into electricity

Thin-film Si solar cell technology

Thin-film Si solar cells on glass

Power plant

Roof integration and new designs

Thin-film Si solar cell technology

Flexible thin-film Si solar cells

Roof integration

Consumer electronics

Stand-alonesystem

Flexible module

-20

-15

-10

-5

0

5

-0.2 0.0 0.2 0.4 0.6 0.8 1.0Voltage [V]

Cur

rent

den

sity

[mA

cm-2]

initial

degraded

p-i-n a -Si:H Initial Degradedsolar cell

Jsc [mA/cm2] 16.2 15.7Voc [V] 0.75 0.74fill factor 0.69 0.64efficiency [%] 8.4 6.3

• Creation of extra metastable defects in a-Si:H under illumination

• Extra trapping and recombination centres

• Initial versus stabilized efficiency

Thin-film Si solar cell issues

Degradation of a-Si solar cells

Thin-film Si solar cells challenges

Increasing efficiency

Light trapping techniques• Textured substrates - scattering• Back reflector• Novel approaches

Multi-bandgap concept• Low band-gap materials

Suppressing degradation

Stable material• pc-Si:H, μc-Si:H or poly c-Si• New deposition techniques• Hydrogen diluted silane

Multi-junction concept• Tandem solar cells

300 500 700 900 1100 1300 1500Wavelength [nm]

Pho

ton

flux

[1027

ph

/ m3 s

]

4.13 2.48 1.77 1.38 1.13 0.95 0.83

Photon energy [eV]

5.0

4.0

3.0

2.0

1.0

0.0

a-Si a-SiGe

AM1.5 global solar spectrum

Increase efficiency

Multi-bandgap solar cell concept

Efficient use of solar spectrum

EFEner

gy

p ni

a-Si

EF

p ni

a-Si

EF

p nin pi

a-Si a-Si

Multi-junction solar cell concept

EF

p nin p

a-Si

i

a-SiGe or μc-Si

Suppress degradation

Thin-film Si solar cell structures

uc-Si:H bottom absorber

Ag ZnO

surface textured - TCOZnO:Al

glass

a-Si:H top absorber

a-Si :HGe middle absorber

surface textured TCO-

uc-Si:H absorber

Ag ZnO

surface textured - TCOZnO:Al

glass

a-Si:H absorber

interlayer

surface textured TCO-

glass

uc-Si:H layers

back metal contact (Ag)

pin

ZnO

single-junctionamorphous (a-Si:H)microcrystalline (uc-Si:H)

double-junctionmicromorpha-Si:H/uc-Si:H

triple-junctione.g. a-Si:H/a-SiGe:H/uc-Si:H

Record ηst (confirmed) 9.5% (a-Si) Un. Neuchatel

10.1% (μc-Si) Kaneka

11.7% (a-Si/ μc-Si) Kaneka

12.4% (a-Si/a-SiGe) USSC* 13.0% (Si/SiGe/SiGe) USSC*

Photon management

Proper handling of incident photons which have to

be trapped in the absorber layers of a solar cell

Photon management

Light trapping techniques:• Manipulation of light propagation: multiple passes

Engineering of optically-active layers(back and intermediate reflectors, layers for optical matching)

• Light scattering: change direction of propagation

Design of surface texture (random or periodically textured surfaces)

Trap photons in the absorber layer and enlarge their average path

Importance of light trapping

1x

10x

50x

a-Si:H 300 nm

Wavelength (nm)

400 500 600 700 800 900 1000 1100 1200

AM 1

.5 s

pect

rom

(mW

/(cm

2 um))

0

20

40

60

80

100

120

140

160

180

1x13.11 mA/cm2

10 x19.87 mA/cm2

+ 52 %

50 x23.30 mA/cm2

+ 78 %

a-Si:H film

• change of direction• multiple passes

Janez Krc, 2008

Importance of light trapping

1x

10x

50x

uc-Si:H 1 um

Wavelength (nm)

400 500 600 700 800 900 1000 1100 1200

AM

1.5

spe

ctro

m (m

W/(c

m2 um

))

0

20

40

60

80

100

120

140

160

180

1x14.87 mA/cm2

10 x28.27 mA/cm2+ 90 %

50 x35.31 mA/cm2

+ 137 %

uc-Si:H film

Janez Krc, 2008

Light trapping

AP CVD SnO2:F Wet etched ZnO:Al

Standard techniques:• Random surface-textured substrates

Asahi U-type AP CVD SnO2:F, Julich wet-etched ZnO:Al

• Back reflectorThin ZnO layer between Si and metal

Light trapping

State-of-the-art uc-Si:H solar cell:

Wavelength (nm)

400 500 600 700 800 900 1000 1100 1200

AM

1.5

spe

ctro

m (m

W/(c

m2 um

))

0

20

40

60

80

100

120

140

160

180

di-uc-Si:H = 1 um

cell23.22 mA/cm2

10x

surface textured TCO-

glass

uc-Si:H layers

back metal contact (Ag)

pin

ZnO

Janez Krc, 2008

Wavelength (nm)400 600 800 1000

Abs

orpt

ion

loss

es

0.0

0.2

0.4

0.6

0.8

1.0

Rtot

BR

TCOsub.

i-uc-Si:H

p+n

Light trapping

surface textured TCO-

glass

uc-Si:H layers

back metal contact (Ag)

pin

ZnO

State-of-the-art uc-Si:H solar cell: analysis of optical losses using modeling

Janez Krc, 2008

Wavelength (nm)400 600 800 1000

J SC d

ensi

ty d

istri

butio

n (m

A/(c

m2 um

))

0

20

40

60

80

Rtot

BR

TCOsub.

i-uc-Si:H

p+n

available JSC

(from AM1.5)

i-uc-Si:H1) R2) TCO sub3) BR4) p+n

23.208.374.813.902.33

JSC (mA/cm2)54 %20 %11 %10 %5 %

Light trapping

State-of-the-art uc-Si:H solar cell: analysis of optical losses using modeling

Janez Krc, 2008

Light-In projectTUD, Helianthos

ECN, OM&T

Advanced concepts for light trapping

• Wavelength-selective manipulation of reflection and transmission of light at interfaces using 1-D photonic crystals

• Concept of modulated 1-D photonic crystals

• Applied as back and intermediate reflectors

Wavelength (nm)600 800 1000 1200 1400

Ref

lect

ance

0.0

0.2

0.4

0.6

0.8

1.0 100 %

PC_1

50/100 nm

Wavelength (nm)

600 800 1000 1200 1400

Ref

lect

ance

0.0

0.2

0.4

0.6

0.8

1.0 100 %

PC_2

70/140 nm

Wavelength (nm)600 800 1000 1200 1400

Ref

lect

ance

0.0

0.2

0.4

0.6

0.8

1.0 100 %

PC_1 PC_2+

MODULATED PC

Wavelength (nm)

300 400 500 600 700 800 900 1000

Abs

orpt

ance

0.0

0.2

0.4

0.6

0.8

1.0

thin lines - single IR (150 nm ZnO)thick lines - PC stack IR

IRTES projectTUD, TU/e, Helianthos

• Intermediate reflector (IR)

glass substrate

ZnO:Al

a-Si:H cell

uc-Si:H cell

ZnO:B

WP

n-a-Si:HZnO

Simulation results:

ZnO(d = 70 nm)uc-Si:H(d = 20 nm)

Advanced concepts for light trapping

Jsc,top = 9.4 mA/cm2

Jsc,top = 10.1 mA/cm2

Jsc,top = 12,0 mA/cm2

Jsc,top = 10.1 mA/cm2

Light-In projectTUD, Helianthos

ECN, OM&T

• Angle-selective manipulation of light scattered at the rough interfaces using 1-D and 2-D diffraction gratings

Scattering angle (ϕscatt)

-90 -60 -30 0 30 60 90

AD

F T (a.

u.)

0.0

0.2

0.4

0.6

0.8

1.0

P = 700 nmh = 80 nm

Asahi U-type

ϕinc = 0o

ZnO:Al(40" etched)σr � 110 nm

Advanced concepts for light trapping

0 50 100 150 200 250 3007.4

7.6

7.8

8.0

8.2

8.4

8.6

8.8

9.0

Period = 600 nm

Asahi reference

Ave

rage

Effi

cien

cy (%

)

Feature height (nm)

Light-In projectTUD, Helianthos

ECN, OM&T

Average efficiency of 10 best cells plotted versus groove height

Advanced concepts for light trapping

• Angle-selective manipulation of light scattered at the rough interfaces using 1-D diffraction gratings

Light-In projectTUD, Helianthos

ECN, OM&T

0 50 100 150 200 250 3007.47.67.88.08.28.48.68.89.09.29.4

Period = 600 nm 2D period = 500-800 nm

Asahi reference

Ave

rage

Effi

cien

cy (%

)

Feature height (nm)

Advanced concepts for light trapping

• Angle-selective manipulation of light scattered at the rough interfaces using 2-D diffraction gratings

Helianthos project

• Development of low-cost roll-to-roll technology for fabrication of thin-film silicon solar modules (started in 1996)

• Dutch route: Temporary superstrate solar cell concept

By courtesy of Helianthos bv.

Helianthos manufacturing sequence

- Al foil

Al foil + TCO + a-Si:H + back contact + carrier foil

+ series connect + contact wires+ cutting

+ encapsulant

Status Helianthos project

Flexible lab-size tandem moduleFlexible a-Si:H module: ready for production

1st generation modulesSingle junction a-Si:H module ηin > 7%ηst = ~6%

Achieved:2nd generation modulesTandem a-Si:H/μc-Si:H module ηin > 11%ηst = ~10%

Challenge:

By courtesy of Helianthos bv.

Summary

Thin-film Si solar cell technology• Promising future option for large-area low-cost PV

• Expected large increase in production capacity

• Large scale of applications (rigid + flexible)

• Modules with 10% efficiency

Challenges:• Increase efficiency (photon management)

• Development and implementation of novel ideas