August 11-13, 16, 17, 2010 India-U.S. Professorship Award ...physics.unipune.ac.in/announcements/Saini_APS-ShortCourse5.pdf · •a-Si: Moser Baer (Noida, India) “SunFab line”,

(For Educational Purposes Only)

Silicon PhotonicsUniversity of Pune Physics Short Course

August 11-13, 16, 17, 2010

India-U.S. Professorship Award Lectures

Sajan SainiQueens College

City University of New York

© S.Saini (Queens College), J. Michel (MIT) 2010

Sub-Micron Planar Platform - E-P Convergence - Materials Integration

Device Physics - Materials Science

Sponsored by:

The Indo-U.S. Science & Technology Forumand The American Physical Society

62(For Educational Purposes Only)

Lecture 1:

Introduction to Si Photonics

Lecture 2:

Waveguides &

Mode-Engineered Devices

Lecture 3:

Resonators & Photodetectors

Lecture 4:

Modulators & Lasers

Lecture 5:

Photonics in 3rd Gen. Photovoltaics

Electronic-Photonic Integration

Confinement Physics

Scatering mechanisms, Si-compatiblewaveguides

Turns, splitters, rotators, couplers

WDM & standing/traveling wave cavities

Si vs. Ge detectors

Plasma dispersion & electroabsorptionmodulators

III integrated lasers, ultra-high Q, Ge laser

The case for a solar economy

3rd Gen. PV materials & devices

(For Educational Purposes Only)

Applications:Photonics for 3rd Gen Photovoltaics

Availability of solar power

Solar versus combustible energy sources

1st, 2nd, 3rd Generation PV examples

Photonics in PV


Modernity: an Energy Intensive Way of Life

Modern economy is energy intensive: need

cheaper, cleaner sources of power

Visible spectral

emission

from terrestrial surface

India


Solar Powered Energy Economy

Majority of terrestrial surface

plentiful with solar reserves

Power availability (A=1 m2, ~0.3)

Africa, South America, Australia:

~187 W (daytime)

India, Arizona: ~175 W (daytime)

Solar power density on terrestrial

surface

Visible spectral

emission

from terrestrial surface


Why Renewable Energy?

Citizen: electric transportation (long-term) = transport cost

Governments: shift in national security policy

The Planet: reduce green house gas production (CO2, H2O, CH4)

T Climate Change consequences:

Polar ice melting: ocean salinity , alter ocean currents

Warmer atmosphere & oceans: severe hurricanes & blizzards

Warmer ocean: water expands, sea level (20 cm / 100 yrs)

IF polar ice caps melted, sea level 70 m

Solar reserves are abundant resource: 1 hour of sunlight on earth = all the energy used globally bypeople in one year

Solar Energy is long lasting - ~5 billion years

Solar spectrum (on Earth)

!!! Question: how many Si solar panels (PV area) required?


Renewable Energy Sources

Solar1.2 x 105 TW at Earth surface

600 - 1000 TW practical land sites

Biomass5-7 TW grossall cultivatableland not used

for food

Hydroelectric

Geothermal

Wind2-4 TW extractable

4.6 TW gross1.6 TW technically feasible0.9 TW economically feasible0.6 TW installed capacity

12 TW gross over landsmall fraction recoverable

Tide/Ocean Currents 2 TW gross

energy gap~ 14 TW by 2050~ 33 TW by 2100

(© Y. Yi, College of Staten Island, CUNY, 2010)


Coal: the Dirty Opponent

Coal-fired thermal plants consume a disproportionate amount of input power for production

Conversion losses are dominated by thermal plants (coal, natural gas)

Source: U.S. Energy Information Administration (Oct 2008).

http://www.eia.doe.gov/emeu/aer/diagram5.html

U.S. Annual Electrical Energy flow (2008) in Quads

(1 Quad = 1015 BTU ~1018 J)


PV Solar Cell Structure & Materials

Efficiency vs energy for common PV

materials

1st Gen: Si homojunction

Peak absorption in visible spectrum

(92% of PV market)

2nd Gen: increase vis absorption

Amorphous thin film Si

CuInGaSe2 (CIGS), CdTe

Organic PV, Dye-sensitized PV

3rd Gen: device & materials eng. for >30%

Tandem solar cell (broadband absorption)

Intermediate band gap solar cell (sub band

gap absorption)


1st Generation Solar CellsBulk Silicon

• Single crystal, polycrystalline

• ~92% of PV market

• Si homojunction

• ~30% single-junction efficiency (Schockley-Quiesser limit)

• High vis-absorption

• Inefficient UV absorption

• IR photon unabsorbed (below band gap)

• Challenges

– Indirect bandgap

– Decrease impurities, grain boundaries

and dislocations – recombination

– Produce larger ingots, ribbons and

boules

– Increase growth speeds

• Major players

– Sun Power, Shell Solar, BP Solar (U.S.)

– Suntech Power, Yingli, JA Solar, Trina Solar

(China)

– Sharp Corp. (Japan)

– Q-Cells (Germany)

“a rigorous analysis of the worldwide supply position shows there is insufficient silicon feedstock

to meet the planned cell manufacturing capacity expansion, overall PV market growth will be

restricted as a result.” solarbuzz.com



2nd Generation Solar CellsThin Films

• a-Si, CdTe, CI(G)S

• 7% of PV market

• p-n or p-i-n heterojunction(s)

• Deposited by evaporation, sublimation,

spraying, sputtering, electrodeposition, or

chemical vapor deposition

• Challenges

– Improve module Efficiencies!!!

• a-Si: United Solar Ovonic, BP Solar, EPV

(Stabilized eff. 6-8%)

• a-Si: Moser Baer (Noida, India)

“SunFab line”, 2009

• Poly-Si: Kyocera (Japan)

• CdTe: First Solar, Antec Solar

(7-11% module eff.)

• CI(G)S: Shell Solar, Global Solar

(7-13% module eff.)



3rd Generation PVMultijunction Tandem Solar Cells

0 1 2 3 40

10

20

30

40

50

60

70 Eg3Eg2

Eg1

Sola

r P

hoto

n F

lux (

mA

/cm

2

.eV

)

Energy (eV)

Eg1

Eg2

Eg3

Sunlight

Tandem PV Cells use multiple p-n junctions to absorb different ranges of the

solar spectrum and hence reduce photogenerated electron energy loss via

thermalization (phonon emission).



e-

3rd Generation PVOrganic Solar Cells

• Bulk Heterojunction

– Intimate mixture of D/A, usually polymer

(donor) and C60 derivative (acceptor)

– Exciton diffusion length ~ 10 nm

– Want all excitons created within a

diffusion length of interface

– < 5% efficiency

• Challenges

– Lifetimes = thousands of hours

– Device degradation

– Phase separation lowers efficiency

– polymer has low mobility so films are too

thin for full absorption

• Major players: academia, Konarka (U.S.)

MRS Bulletin, Vol 30, Jan 2005

Transparent electrode

Glass

Metal electrode

100 nm

_+



3rd Generation PVDye-Sensitized Solar Cells

• Challenges

– liquid electrolyte is optically dense and cells

leak over time

– highest efficiencies obtained with liquid

electrolyte and Ti foil electrode

– Solid-state cells not as efficient (4%)

• Major players: Konarka

• Claim 6-10% efficiency

• Roll-to-roll hybrid Grätzel/organic cell

• Trying to partner with other companies

Dye-sensitized

J. Am. Ceram. Soc., 80 [12] 3157–71 (1997)

• Grätzel Cell

– Dye injects e- into nanocrystalline TiO2,

dye is regenerated by solid or liquid

electrolyte

– Light absorption and charge transport are

separated

– Up to 12% efficiency

– High surface area = more dye = higher

current



3rd Generation PVConcentrating Solar Cells

Individual Lens: 7.4”x 7.4”

Parquet Size: 47.16” x 38.75”

Material: Acrylic

Focal Length: 11.95” - 12.05”

Focal Point Size: .5” x .5”

Optical Efficiency: 84%

Concept: turn Si PV into a “micro” device

benefit from Moore’s Law (Economy of Scale)

Major players: Sharp Corp. (Japan), SolFocus (U.S.), Spectrolab (U.S.)



Evolution in PV Efficiency



Evolution in PV Efficiency

Source: B. Nelson and S. Robbins, “Introduction to Photovoltaic

Technologies,” Short Course, 34th IEEE PVSC (2009).

Sanyo HIT (Heterojunction with Intrinsic Thin Layer: c-Si + a-Si

(http://solar.sanyo.com/hit.html)


Photonics in 3rd Generation PVNanoparticles: scintillators, intermediate band gap absorbers

S V Kondratenko, et al., “The lateral photoconductivity of Si/Ge structures with quantum

dots,” Semicond. Sci. Technol. v.21. pp.857–859 (2006).

E. Mutlugun, H. Demir et al., “Photovoltaic nanocrystal

scintillators hybridized on Si solar cells for enhanced conversion

efficiency in UV,” Opt. Express v.16(6), p. 3537 (2008).

V. Svrcek et al., “Silicon nanocrystals as lightconverter for solar cells,” Thin Solid Filmsv.451-452, pp.384–388 (2004).

CdSe, Si scintillators: absorb UV and downconvert to

visible light, for Si PV

Ge QD doped within Si: sub-band gap absorption, Type

II offset minimizes carrier recombination


Photonics in 3rd Generation PVNanoparticles: tandem, hot carrier cells

Templated lattice constant: artificial band gap

materials

Match Fermi levels to metal contacts: reduces

carrier thermalization

G. Conibeer, M. Green et al., “Silicon nanostructures for third generation photovoltaic solar cells,”

Thin Solid Films, v.511-512, pp.654-662 (2006).


Photonics in 3rd Generation PVPhotonic Crystals: scattering incident light into solar cell plane

‘Fano resonances’ scatter incident wavelengths into “high dielectric states”

J. Song, X.W. Sun et al., “Tunable Fano resonance in photonic crystal

Slabs,” Opt. Express, v.14(19), p.8812 (2006).


Renewable Energy: Long-term Concerns

Geology and location

Solar tracking

Efficient battery storage and low

resistance transport

Smart grid for green energy?

Solar thermal

Hydrogen generation


Documents

August 11-13, 16, 17, 2010 India-U.S. Professorship Award ...physics.unipune.ac.in/announcements/Saini_APS-ShortCourse5.pdf · •a-Si: Moser Baer (Noida, India) “SunFab line”,