201 icaer ppt_sonali_v1

Sonali Das, CEGESS, BESUICAER, IIT-B, 11 Dec 2013

Mixture of metal and dielectric nanoparticles for improved performance of silicon solar cell

Sonali Das, Prasenjit Dey, Avra Kundu, S. M. Hossain, H. Saha, Swapan K. Datta

DST SOLAR HUBCentre of Excellence for Green Energy and Sensor Systems

Bengal Engineering and Science University, Shibpur, Howrah

IV th International Conference on Advances in Energy Research10-12 December 2013 @ IIT Bombay, Mumbai


Contents Towards high efficiency solar cell

Nanoparticles – A Brief Review

Choice of Nanoparticles

Objectives

Design, Simulation, Optimizations

Experiments carried out

Conclusion


Requirements for high efficiency silicon solar cells


Requirement 1

Key requirement 1

Maximized injection of photons into the cell by designing an antireflection coating at the front

surface which reduces reflection coefficient without significant loss of energy due to Joule

heating.

A single transparent dielectric layer as Anti reflective coating on TOP surface of Silicon

Reduce reflection to ~18%

Bare Silicon is highly reflective

Avg. reflection ~30%


Light absorption in silicon solar cell becomes critical as the thickness of an absorber layer is

decreased to reduce cost.

300 400 500 600 700 800 900 1000 11000.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

Fra

cti

on

of

inje

cte

d p

ho

ton

th

at

is a

bso

rbed

Wavelength (nm)

200m

20m

2m

1m

Key requirement 2

Maximized absorption of

injected photons with better

collection by silicon

Requirement 2

To compensate for lower light absorption in such physically thin devices, we have to

incorporate light-trapping schemes in order to increase their optical thickness.


Texturization – fulfilling both requirements

Textured on the TOP surface of Silicon

Reduce reflection to ~13%Light absorption due to path length enhancement

Texture dimensions are of the order of 1 – 10 µm. Such large-scale geometries are not suitable for thin-film cells ( 1-2 µm ).

It increases minority carrier surface recombination due to greater surface area reducing the collection efficiency of the photo-generated carriers.

Novel approaches are needed for photon injection management and light trapping without texturing in both thick and thin silicon solar cells.

Textured front surface of Silicon with ARC

Reduce reflection to ~3-4%


Recently, nanoparticles have been proposed as an

alternative method to reduce reflection and achieve light

trapping in silicon solar cells

H.A.Atwater and A.Polman , Plasmonics for improved photovoltaic devices , Nature Materials , 9 , 205 – 213 ( 2010 )


Nanoparticles (NPs) A Brief Review


Schematic Representation of a NPDirection of incident light

R

T

Cext

Csca

Cabs

Csca (Scattering Cross- section):The area, on which if the radiation is incident, will

scatter the same power as the power scattered by the particleCabs (Absorption Cross- section):The area, on which if the radiation is incident, will

absorb the same power as the power absorbed by the particle

Cext=Csca+Cabs

Scattering and absorption cross-sections depend on polarizability


α is the polarizability of the particle, given by

/ 13

/ 2p m

p m

V

V is the particle volume , εp is the dielectric function of the particle and εm is the dielectric function of the embedding medium

Resonant enhancement happens when |2 εm + εp | is minimum

At the plasmon resonance frequency, polarizibility becomes maximum.

Scattering becomes maximum well exceeding the geometrical cross section

of the particle at the plasmon resonance.

Polarizability


Features of NPs needed for their incorporation in Si Solar Cell

Attributes of NPs needed for their incorporation in Si solar cell

Csca Cabs

Efficient scattering in the 300nm-1100nm wavelength region

Absorption leading to joule heating should be minimized


Choice of Nanoparticles

Sonali Das, CEGESS, BESUICAER, IIT-B, 11 Dec 2013Simulated optical extinction (black lines), scattering (blue lines) and absorption (red lines) efficiencies of 100 nm diameter metal spheres in air .

Choice of metal nanoparticles


Choice of dielectric nanoparticles

Silica (1.46) d=100nm

Silicon nitride (2.05) d=100nm

Titanium dioxide (2.62) d=100nm

Silica Nanoparticles can be easily realized by well known Stober technique


Key parameters

Injection of incident photons

Absorption of injected photons: Path length enhancement

Collection of electron hole pairs from absorbed photons

Key parameters to be monitored for achieving high efficiency solar cell


Injection into substrate Ag NPs (100nm radius)

300 400 500 600 700 800 900 1000 11000.8

1.0

1.2

1.4

1.6

1.8

Inj w

ith

na

no

/Inj w

ith

ou

t n

an

o

wavelength (nm)

bare si 10% 20% 40% 60% 78%

300 400 500 600 700 800 900 1000 11000.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

Inj w

ith

nan

o/In

j wit

ho

ut

nan

o

wavelength (nm)

bare si 10% 20% 40% 60% 78%

Silica NPs (100nm radius)

OnSi

For bare Si


Path length enhancement inside substrate

300 400 500 600 700 800 900 1000 1100

1.0

1.1

1.2

1.3

1.4

1.5

1.6

(Pa

/Pt)

na

no

/(P

a/P

t)b

are

wavelength (nm)

bare si 10% 20% 40% 60% 78%

300 400 500 600 700 800 900 1000 11001.000

1.005

1.010

1.015

(Pa/

Pt)

nan

o/(

Pa/

Pt)

bar

e

wavelength (nm)

bare 10% 20% 40% 60% 78%

OnSi

Ag NPs (100nm radius) Silica NPs (100nm radius)

For bare Si


Summing it up…Metal Nanoparticle Dielectric Nanoparticle

Scattering Efficiency

Angular Scattering

Path length enhancement inside substrate

Enhanced Photon Absorption due to path length enhancement

No ohmic losses

Phase matching between layers


Therefore, a judicious mixture of metal and dielectric

nanoparticles may help us in utilizing the positive aspects of

each of the nanoparticles.


ObjectivesTo enhance

Injection of incident photons

Path length of injected photons : Absorption of injected photons

Collection of electron hole pairs

Optimization of

Material of nanoparticles(silver or silica)

Size of nanoparticles

Area Coverage of nanoparticles


Design Methodology

After obtaining an optimum size and coverage of the silver nanoparticles,

the remaining bare surface of the silicon is covered with an optimum size of

silica nanoparticles for reducing the reflection loss even further.

Silver nanoparticles of varying size have been placed on top of silicon

substrate with different area coverage for obtaining the maximum

absorption of incident power inside silicon.

Silicon

Direction of incident light


Simulation ModelLumerical FDTD Solutions, www.lumerical.com

Pabs/Pinj is the most important term to be monitored

abs

inj

Power Monitor 2 - Power Monitor 3P absorbed power within the given silicon block

P injected light into silicon Power Monitor 2


av

abs

inj with _ nano

Wcos( )

P ( )ln 1

P ( )

bb

avav

av

WW cos1100nm

cos bn0W

300nm cosfn _ with _ nano bn

1 R eNumber _ of _ absorbed _ photons 1 e T( )N ( )d

1 R R e

b2W zz

bn0 2 z

bn fn _ with _ nano

e R eGeneration _ Rate G ,z N ( )T( ) ( )

1 R R e

1100nm 1100nmph

0300nm 300nm

JEHPs d T( )N ( )IQE( )d

q

Analytical CalculationsFrom the simulations…

Subsequently,

the path length of the oblique light into the solar cell

Finally,


To summarize, an increase in the collected EHPs is obtained for 15±5%

coverage of 100nm particles and 40±5% coverage of 50nm particles.

Optimization: Silver Nanoparticles

Size of nanoparticles

(radius: 10nm – 200nm)

Area coverage of

nanoparticles (10%-50%)


Case 1 Case 2 Case 3 Case 4 Case 5

1.4

1.5

1.6

1.7

1.8

Num

ber o

f ele

ctro

n- h

ole

pairs

col

lect

ed (X

1021

/m2 /

s)

Cases

Case 1 100nm Silver: 20% coverage

Case 2 25nm Silica: Full coverage

100nm Silver; 20% coverage 25nm Silica: RemainingCase 3 50nm Silica: Full coverage

100nm Silver; 20% coverage 50nm Silica: Remaining





Case Study


Experiments carried out


Preparation of Silica Nanoparticles by modified Stober technique

HYDROLYSIS

POLYCONDENSATION

3

_ _4 2 2_11 12_

( ) ( ) 2suspension in ethanolpH NH

Si OH SiO sol H O

3

_ _2 5 4 2 4 2 5_11 12 _

( ) 4 ( ) 4suspension in ethanolpH NH

Si OC H H O Si OH C H OH

CENTRIFUGATION AND WASHING IN PREPARED MEDIUM 2-3 times

DRYING OF CENTRIFUGED PARTICLES at 500C for 5 hours

ULTRASONICATION in desired medium for final COLLOIDAL SOLUTION

Hydrolysis of Tetra ethyl ortho- silicate

FESEM image of silica nanoparticles


Size Variation of Silica Nanoparticles

As alcohol molecular weight increases from methanol to propanol, the average particle size increases from 80nm to 500 nm. This can be attributed to a change in viscosity or the polarity of the solvent caused by the increased molecular weight of the alcohol.

It is observed that the average particle size is 80nm for methanol, 300nm for ethanol and 500nm for propanol.

DLS by silica NPs prepared in different alcohol media


FTIR of Silica Nanoparticles

FTIR of prepared silica NPs in ethanol medium spin coated on bare polished Si wafer measured by Shimadzu Solid Spec 3700 UV-VIS-NIR Spectrophotometer (Inset: FTIR of bare polished Si wafer).

The FTIR spectra of the colloidal silica NPs show prominent absorption band arising from asymmetric vibration of Si-O-Si at the wave number 1090 cm–1.

C-O bonding (1400-1800 cm–1) and Si-C (2357 cm–1) are also observed due to bare polished Si wafer itself (inset of Figure 1).


Silver Nanoparticles from Nanocomposix

DLS by silver NPs of NanocomposixFESEM image of silver nanoparticles


Silica Nanoparticle Silver NanoparticleDiameter 300nm 100nm

Mass Concentration 17mg/ml 0.020mg/mlParticle

Concentration453.7E+09

particles/ml3.7E+09 particles/ml

pH of the solution 11 5.7Particle Surface Uncoated PVP

Solvent Ethanol DI Water

Nanoparticles’ Specification


ResultsExperiments have been carried out by preparing a colloidal solution of 1:1::silver: silica

nanoparticles. The mixture of the colloidal solution was then spin coated on the bare silicon

surface.

FESEM image showing a mixture of silver and silica nanoparticles


Results (contd.)

Reflection measurements of

the samples have been done

using Bentham PVE 300

Photovoltaic

Characterization equipment.

It is seen that the average

reflectance of the bare

surface (~ 30 %) decreases to

a value of about 12%.


Further, cell has been fabricated with this coated wafer.

An enhancement in short-circuit current density of about 28% is obtained from a

baseline value of 14.5mA/cm2.

Results (contd.)


Conclusions

Maximum enhancement in absorption occurs with a mixture of 100nm radius silver

nanoparticles having 20% coverage along with 50nm radius silica nanoparticles

covering the remaining bare surface.

Experiments are currently underway to obtain the desired design coverage with

synthesized silver and silica nanoparticles.


Acknowledgement

Department of Science and Technology (DST) for

providing necessary financial support.

All members of CEGESS


THANK YOU


A new approach: Plasmonic nanoparticleOscillating Electromagnetic energy

e- +


Why nanoparticles on the top

Reduced Reflection

Increased Absorption near the Junction

Forward Scattering

Backward Scattering

Path length


Choice of nanoparticles

Metal High scattering efficiency Presence of dipolar resonance

Suffers from ohmic dissipation and absorption loss

Dielectric Low scattering efficiency Absence of dipolar resonance but presence of higher quadrupolar modes No ohmic dissipation and absorption loss

Metal nanoparticles can reduce reflection with increased photon injection when applied on the top of bare Si. But its not the case when applied on the top of an optimized AR layer because of the loss of energy due to the metal absorption itself.

So, dielectric nanoparticles have been chosen.


300 400 500 600 700 800 900 1000 11000.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

(Tf)n

an

o /

(Tf)

nit

rid

e

wavelength (nm)

nitride on bare 5% 10% 20% 30% 40% 50% 60% 70% 78%

Further for Ag NPs on nitride coated Si SCs...

Enhancement of injection w.r.t the bare siliconDegradation of injection w.r.t the nitride silicon

Metal (Ag) nanoparticles may not be beneficial for

enhancement in efficiency of ARC silicon solar cells .

100nm radius Ag NP


Cross-sections and efficiencies of NPFor small spherical NPs (sizes<1/10 th the wavelength (λ) of light), the scattering, absorption and extinction cross sections/efficiencies

2Im( )absC

241 2

( )6scaC

2sca

sca

CQ

a

2abs

abs

CQ

a 2

extext

CQ

a

ext sca absC C C

The dynamic depolarization effect becomes predominant for larger radius particles where all the electrons do not oscillate in phase

For large spherical NPs (sizes>1/10 th the wavelength (λ) of light), the scattering, absorption and extinction efficiencies (by Mie Theory)

2 22

1

2(2 1)(| | | | )sca n n

n

Q n a bx

21

2(2 1) Re( )ext n n

n

Q n a bx

abs ext scaQ Q Q

where an and bn are the Mie Coefficients, n is the index running from 1 to ∞ and x is the size parameter

For infinite series, n is truncated to nmax.

1/3max 4 2n x x

201 icaer ppt_sonali_v1

Technology

Transcript of 201 icaer ppt_sonali_v1