Advanced Cell Technologies for Concentrated PhotovoltaicsOutline • Introduction to concentrated photovoltaics (CPV)Introduction to concentrated photovoltaics (CPV) • CCsoatecoogyPV

Advanced Cell Technologies Advanced Cell Technologies for Concentrated for Concentrated

PhotovoltaicsPhotovoltaics

Homan YuenSolar J nction CorporationSolar Junction Corporation

International Solar Energy Technology ConferenceInternational Solar Energy Technology ConferenceOctober 27, 2011 - Santa Clara, CA

PROPRIETARY AND CONFIDENTIAL. PROPERTYOF SOLAR JUNCTION. PRESENTED TO CAPRICORNPROPRIETARY AND CONFIDENTIAL. PROPERTYOF SOLAR JUNCTION. PRESENTED TO CAPRICORN0

Outline

• Introduction to concentrated photovoltaics (CPV)• Introduction to concentrated photovoltaics (CPV)

• CPV solar technology – the multijunction solar cellC so a tec o ogy t e u t ju ct o so a ce

• Different flavors of multijunction technologies

• Solar Junction’s leading 43.5% efficient solar cell

• Impacts on system performance and integration

• Parting thoughts

International Solar Energy Technology Conference – 10/27/11 – Santa Clara, CA 1Solar Junction

Solar Landscape Today

Silicon PV Thin Film PV

Concentrating Solar Thermal Concentrating PV (CPV)


What is CPV?

Concentratingoptics

• Employs low-cost optics to concentrate solar flux 500X – 1500X

High efficiency cell and receiver

1000 suns illumination

G. Kinsey, 37th IEEE PVSC Seattle 2011

solar flux 500X 1500X

• Semiconductor cell is only 10-20% of CPV system BOM cost

• Lowest levelized cost of electricity (LCOE) and highest annual energy harvest of any solar technology in sunny locations

Example packaged high efficiency solar cell from Solar Junction


Why Use Concentration?

• Reduce overall cost of the semiconductor material with respect to the entire system costy

• Enables you to put more advanced cell technologies with higher efficiencies without increasing total costI f t d t b i i th t t d t ffi i i• In fact, reduce cost by increasing the power output due to efficiency gains

• Continue to drive down costs with increasing efficiency

15%

CPV vs Flat Plate Cell Cost

50%50%

15%Cell Cost

Rest of85%

Rest of Module Cost


Different CPV Systems and Technologies


Low Concentration vs High Concentration

• CPV has become a mainstream technology• CPV has historically referred to systems with >100x concentration levelsCPV has historically referred to systems with >100x concentration levels• Different technology with <50x concentration called Low Concentration PV

or LCPV• Based on reflective troughs to increase sunlight levels on silicon cells• Important to note the differences in technologies when doing energy and

cost analysescost analyses


Sunpower 7x system Skyline Solar 14x system

Advantages of CPV – Energy Output

Most power generated per day and most power generated during peak usage.

CPV


Advantages of CPV - Efficiency

CPV i i ffi i t d d till h h ffi i h d


CPV wins in efficiency today and still has much efficiency headroom

Multi-Junction Cells Will Continue to Push Upwards

Most other technologies have hit their efficiency limits, but multi-junction technology still has j gysignificant headroom into the mid/upper 40%s, up to 50%


Advantages of CPV – Minimal Heat Degradation

• Solar cells do not operate at test conditions! They operate at elevated temperature.• CPV has the lowest degradation from the rated power compared to silicon and thin film.g p p


CPV Consortium – SolarExpo CPV Workshop – May 4, 2011

How Can CPV Become Even Better?

Biggest levers to further reduce cost of CPV and continue acceleration of acceptance:acceptance:• Concentration• Increased volumes• Efficiency

Where can the biggest efficiency gains be made?Where can the biggest efficiency gains be made?

The heart of the CPV system – where all the power is madeThe heart of the CPV system – where all the power is made

Multi Junction Solar CellMulti-Junction Solar Cell


How Multi-Junction Cells WorkEnergy Conversion

EfficiencyElectrical power (Output)

Light power (Input)=

Energy Conversion Efficiency of Silicon Cell

Energy Conversion Efficiency of MJ Cell

Silicon1 Junction Silicon Solar Cell

3 Junction Solar Cell Stack

Material1

Higher solar cell efficiency

Material2

Material3


Cell Technologies

Solar Junction

Solar Junction Others“Traditional” Metamorphic Inverted Higher voltage design• Lattice Matched• InGaP/GaAs/InGaAsNSb• NREL verified at 43.5%• Roadmap to 50% in 6J

• Bifacial Cells• Quantum Well• Quantum Dot• Intermediate Bandgap

• Lattice Matched• InGaP/(In)GaAs/Ge• 50% overdrive in J3

p• Higher current/lower

voltage• Metamorphic J1 & J2• InGaP/(In)GaAs/Ge

Metamorphic• Higher voltage design• Metamorphic J3• InGaP/(In)GaAs/InGaAs

• Roadmap to 50% in 6J-design

Eff 37-39% 39.8% >42% >42% 36-42%

Jsc 7.19 A/cm2 7.5 A/cm2 7.1 A/cm2 7.1 A/cm2 varies


Voc 3.21 V 3.12 V 3.5 V 3.5 V varies

Conventional Triple Junction Cells on Ge

All epilayers grown lattice-matched to Ge

Ge junction produces ≈ 2x

All epilayers grown lattice matched to Ge.J3 is diffused bottom junction in Ge substrate.

J1: J ≈ 14 mA/cm2

j prequired current at expense of low output voltage (V ≈ 0 27 V at 1 sun)J1: Jsc≈ 14 mA/cm

J2: Jsc≈ 14 mA/cm2

(Voc ≈ 0.27 V at 1-sun)

sc /

J3: Jsc > 25 mA/cm2

J1 = InGaP J2 = In0.01Ga0.99As J3 = Ge


Advanced Design – Decrease J1/J2 Bandgap

Higher current but lower voltage compared to conventional 3J cell

J1: Jsc≈ 15-16.5 mA/cm2

p

J2: Jsc≈ 15-16.5 mA/cm2J2: Jsc 15 16.5 mA/cm

J3: Jsc≈ 15-16.5 mA/cm2

J1 = InGaP J2 = InGaAs J3 = Ge


Cell Technologies

Solar Junction








Eff 37-39% 39-40% >42% >42% 36-42%



Voc 3.21 V 3.12 V 3.5 V 3.5 V varies

Bandgap Tuning – Materials Selection

A id i d d f i i h

Non-Lattice-Matched Structure Lattice-Matched Deposition Structure

• Accessing optimal bandgaps requires integrating incompatible materials (different lattice-constant materials)

• Lattice-constant transition layer (metamorphic buffer layer)

• Strain creates crystalline defects, reduces yield and reliability

• Avoids strain and defect generation common with metamorphic structures

• Standard, proven approach used by the compound semiconductor industry for the last 35 years

y , y y

• Increases epi and wafer-processing costs• Increases yield, reliability and efficiency

• Lowers cost

Clean transition -h

GaInNAsGaInNAs

L tti t t a

aX-sectionX-section

coherence across interface

a

GaAsGaAs

Lattice constant transition layer

a

a

Solar Junction’s 42% and higher efficiency roadmap requires no new materials creation


p q

Advanced Design – Increase J3 Bandgap

Approximate current matching achieved with boost in output voltage (> 200 mV at 1-sun)

J1: Jsc≈ 14 mA/cm2 compared to Ge J3



J1 = InGaP J2 = GaAs J3 = ???


Cell Technologies

Solar Junction








Eff 37-39% 39-40% >42% >42% 36-42%



Voc 3.21 V 3.12 V 3.5 V 3.5 V varies

Cell Technologies

Solar Junction

Solar Junction Others“Traditional” Metamorphic Inverted Higher voltage design• Lattice Matched• InGaP/GaAs/GaInNAsSb• NREL verified at 43.5%• Roadmap to 50%






• Roadmap to 50%

Eff 37-39% 39-40% >42% >42% 36-42%



Voc 3.21 V 3.12 V 3.5 V 3.5 V varies

Bandgap Tuning – Materials Selection

A id i d d f i i h

Non-Lattice-Matched Structure Lattice-Matched Deposition Structure

• Accessing optimal bandgaps requires integrating incompatible materials (different lattice-constant materials)

• Lattice-constant transition layer (metamorphic buffer layer)

• Strain creates crystalline defects, reduces yield and reliability

• Avoids strain and defect generation common with metamorphic structures

• Standard, proven approach used by the compound semiconductor industry for the last 35 years

y , y y

• Increases epi and wafer-processing costs• Increases yield, reliability and efficiency

• Lowers cost

Clean transition -h

GaInNAsGaInNAs

L tti t t a

aX-sectionX-section

coherence across interface

a

GaAsGaAs

Lattice constant transition layer

a

a

Solar Junction’s 42% and higher efficiency roadmap requires no new materials creation


p q

Bandgap Tuning vs Atomic Spacing

Existing Materials

By adding appropriate amounts of nitrogen and indium to GaAs, you can obtain a material lattice-matched to GaAs ormatched to GaAs or Ge and have a lower band gap.

Bandgap tunability is important in maximizing power generation in


real world conditions

Cell Technologies

Solar Junction

Solar Junction Others“Traditional” Metamorphic Inverted Higher voltage design• Lattice Matched• InGaP/GaAs/GaInNAsSb• NREL verified at 43.5%• Roadmap to 50%






• Roadmap to 50%

Eff 37-39% 39-40% >42% >42% 36-42%



Voc 3.21 V 3.12 V 3.5 V 3.5 V varies

Solar Junction

• Founded in 2007 to develop and manufacture multi-junction solar cells for CPV systems

• Headquartered in San Jose, California• Fully capable factory with 14 MW/year capacity

• Substrates in solar cell product outSubstrates in solar cell product out• Standard semiconductor fabrication• No need to expend extra capital or effort on

building custom equipmentg q p• Great team of people


Solar Junction World Record

• World Record Efficiency 400-600 suns 43.5%• >43% at 1000x• >42% at 2000x• ~3.5V at 1000x

• Standard 5.5mm production cell• Measured by NREL (Colorado) and• Measured by NREL (Colorado) and

Fraunhofer (Germany)• Higher efficiency through higher voltage (not

hi h t)higher current)


Advantages of Solar Junction Cell Technology

• Higher efficienciesHi h lt (l I2R l b tt i t t hi )• Higher voltage (less I2R losses, better inverter matching)

• 5-10% more power over current products

• Roadmap to future technologies• Ability to obtain correct band gap combinations for 4J/5J…• Proven reliable lattice-matched paradigm

• Band gap tuning to increase energy harvesting forBand gap tuning to increase energy harvesting for real world conditions

• Operation at temperaturep p• Integration with system optics• Geographic and environmental affects on spectra


Materials Platform: Full Bandgap Tunability

Standard materials for UV to Near IR (1.4 eV) Plus - Solar Junction’s dilute nitride absorber from 0.8 to 1.4 eV Plus - Germanium out to 0.67 eV Result Fully obtainable band gap combinations resulting in optimal 3J, 4J, 5J….

designs for any situation and for future advanced architecturesdesigns for any situation and for future advanced architectures

UV-Vis Vis-NIR

NIR-IR

InAlGaP AlGaAs

GaInNAs

IRGeGe


Operation at Temperature

• Solar cells do not operate at room

1.6

temperature

• At elevated temperatures, the

1

1.2

1.4

m E

ffici

encysemiconductor band gap decreases

reduction in voltage• CPV has less power output degradation

0.4

0.6

0.8

xter

nal Q

uant

um

Increasing T

at temperature compared to silicon and thin film

• Much higher voltage

0

0.2

350 450 550 650 750 850 950Ex

Wavelength (nm)

• Shifting band gaps also leads to a shifting in current balancing

• Importance of being able to tune band• Importance of being able to tune band gaps around to redistribute current at the operating temperature


Integration with System Optics

• Some slight reductions in transmission in the system optics due to y plenses or reflective elements

• Another instance where adjusting the band gaps is critical inband gaps is critical in maximizing energy harvesting

•V. Rumyantsev, “Solar concentrator modules with silicone-on-glass Fresnel lens panels and multijunction cells,” Optics Express, Vol. 18, No. S1, 26 April 2010, pp. A17-A24.


Adjustments for Environment or Geography

Dimroth et al., IEEE PVSC 2010.

Spectral changes caused by:• Geographical location• Geographical location• Time (hour, day, month) air mass• Water vapor• Atmospheric aerosols, etc.

Tunable bandgaps can enable multi-junction designs which account for varying solar spectra


for varying solar spectra

Parting Thoughts

• After a period of intense development, CPV is at a market inflection pointp

• We have seen >300 MW of CPV announcements in 2011

• Put solar where the sun is!• High sun locations are the fastest growing areas for general solar• High sun locations are the fastest growing areas for general solar• CPV wins in high sun areas (lowest LCOE)• Market reports: CPV is the fastest growth segment of solar

CPV i i i b

CPV target areasCPV target areasCPV target areas

• CPV is winning because • Produces energy in the late afternoon when electricity demand peaks (i.e.

when electricity is most expensive)( )• Superior temperature coefficients (high sun areas happen to also be HOT)

• Is cost competitive TODAY

• Cell plays a dominant role in increasing energy output and decreasing costs

• High efficiency is the dominant lever • Band gap tunability is critical for real world operation


g p y p

Thank You!Thank You!Thank You!Thank You!

PROPRIETARY AND CONFIDENTIAL. PROPERTYOF SOLAR JUNCTION. PRESENTED TO CAPRICORNPROPRIETARY AND CONFIDENTIAL. PROPERTYOF SOLAR JUNCTION. PRESENTED TO CAPRICORN32

Documents

Advanced Cell Technologies for Concentrated PhotovoltaicsOutline • Introduction to concentrated photovoltaics (CPV)Introduction to concentrated photovoltaics (CPV) • CCsoatecoogyPV