solar cells fabrication technologiesinst.eecs.berkeley.edu/~ee143/fa10/lectures/lec_26.pdfminimize...

Professor N Cheung, U.C. Berkeley

Lecture 26EE143 F2010

Solar Cells Fabrication

Technologies

1

•Crystalline Si Cell Technologies

•Amorphous Si Cell Technologies

•Thin Film Cell Technologies

For a comprehensive tutorial on solar cells in general,

see www.udel.edu/igert/pvcdrom



Global Energy Sources projection

Source: World Energy Council



3

The Growth Rate Captures the Attention

Source: AMAT



Solar Facts

•The earth receives more energy from the sun in just

one hour than the world uses in a whole year.

•1% of the land today used for crops and pasture could

supply the world's total energy consumption.

•The Sun provides 1020 Watts/meter² peak power at sea-

level

Cell efficiency of 10% translates to ~100W/meter2



Commonly Known Solar Cell Materials



Fraunhofer



7

Beside efficiency, there are other considerations for ultilization



Projected Module Cost



9

Energy Content

EG silicon ~ 200 kWh/kg

Solar Grade Si ~ 50kWh/kg

MG silicon ~ 20kWh/kg

Richard Corkish ,Solar Progress, (1997)

Energy Payback time

Monocrystalline Si cell ~ 4 years

Polycrystalline Si cell 1.6 to 2.7 years

Amorphous Si cell 0.9 to 1.6 years.



10

Crystalline

Silicon

Amorphous

SiliconCIGS CdTe Organic

Conversion

Efficiency13-18% 5-10% 10-12% 10.5% 5%

Current cost

per Watt* $2.5-3.5 $2-2.5$0.6

(predict)

$1.3

<$1

(predict)

Material

ShortageNo Silane Indium Te(?) No

Toxic

SubstanceNA NA

Cadmium

Selenium

Cadmium

TelluriumNA

Reliability Excellent Fair Good Good Poor

Company in

the field

Suntech,

SunPower

AMAT,

Dupont

Nanosolar,

SolyndraFirst Solar Konarka

Comparison of commercial PV



•Crystalline solar cells are usually wafers, about 0.3 mm thick, sawn from Si

ingot

• 15% efficiency cells deliver

15 to 60 W/m² or 0.45-1.35

kWh/m²/day (annual day and

night average) in North

America

Si Crystalline Solar cells are just large area semiconductor diodes



12

From Ingot to Module



13

From Ingot to Module (cont.)



14

From Sand to Silicon

Process generates four tons of silicon tetrachloride

liquid waste for each ton of polysilicon produced.



15



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17

Minimize Kerf Loss



18

Generic Crystalline Si Cell Processing

Al-Ag paste

* Al-Ag fuses through SiNx to form ohmic contact



19

Backside Al contact

(BSF= back surface field p+ layer)



20

Max T =950C

Belt Furnace



50 MW fab cell line.

(Source: Applied Materials)



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25

Antireflection Coating Materials



26

Diagnosis of Crystalline-Silicon Solar- Cells Utilizing Electroluminescence: save

production costs by sorting out defective solar-cells in an early stage



27

Module

Packaging

Source: Spire Corp



Crystalline Si on Glass (CSG) Solar Cell

* All fabrication done with Laser processing and low-temperature PECVD



29

Sliver Cell

A wafer (assume 150mm diameter) configured as a conventional solar cell has an area

of 177cm2. However, the same wafer, when processed to produce Sliver® cells, can be

used to cover up to 5,000 cm2 of module area, which is 30 times better than for

conventional technology.



Both silicon and thin-film PV solutions require a reduction in cost/watt. (Source: Applied

Materials)

Motivation for amorphous Si Cell



Rigid and Flexible a-Si Solar Cells

Cell efficiency, h = Voc × Jsc × FF

Pin

i- a-Si:H

Textured

TCOZnO

p- a-

SiC:H

n- a-Si:H

30% T Ag

Glass / TCO / p / i / n / Ag SS / ZnO / p / i / n /Ag

Opaque

(SS/Kapton)

Glass

Voc Doped layers

Jsc i-layer defect

density

Light trapping

FF i-layer defect density

Interfaces



32

Amorphous Si Deposition



33

Amorphous Si Deposition



34

Source: ULVAC Solar

a-Si Cell Manufacturing



35

Source: AMAT

Conceptual a-Si Cell Fab



37

CIGS Solar Cells



38



39

Source: pmc.org.tw

CIGS Manufacturing



40



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43

Source: Ascent Solar

Roll-to-Roll Manufacturing



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45

Needs MBE , MOCVD, or Layer Transfer



Technology Evolution

c-Si

thin film

"New Concepts"

0

500

1000

1500

2000

2500

3000

3500

0

20

40

60

80

100

120

140

2002 2005 2010 2015 2020 2025 2030

MW GW30%p.a. 25%p.a.

46

RENEWABLE ENERGY FOR EUROPE - RESEARCH IN ACTION



Q: What are the major differences between

PV fabrication and IC/MEMS fabrication ?

•Patterning (alignment, size control)

•Doping

•Contact Formation

•Metallization

•Planarization

Q: What other process modules are not

commonly used in IC/MEMS fabrication ?

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