Plasmonic assisted optical absorption
enhancement in thin films
a theoretical perspective
Aparajita Mandal

JRF, departmen...
ICSEP
19-21 dec. 2012



Outline

Plasmonics:

• Goal of the present work
• Simulation Model

• Results and Interpretatio...
Plasmonics

Localized Surface plasmon:
The stationary oscillation of conduction electrons confined
on a nano sized metal b...
ICSEP
19-21 dec. 2012

Plasmonics

Particle size dependence
• Plasmonics: Particle Size dependence
Electrostatics
+
++ ++
Dipolar mode

R<< λ

-- - - Phase retardation
across the vol...
Advantages
• Local field enhancement (Light can be confined to a volume which is much
smaller the wavelength).
•

Enhanced...
ICSEP
19-21 dec. 2012

Mie Theory

Overall scattering or absorption cross section σ scat/abs for a single NP as a sum of t...
ICSEP
19-21 dec. 2012

Effects of higher order modes on extinction spectra


Higher order modes introduce additional peak...
ICSEP
19-21 dec. 2012

•

For an array of MNPs

Electromagnetic coupling exists between MNPs, strength of which is
determi...
ICSEP
19-21 dec. 2012

Effect of inter-particle coupling on extinction
spectra
•

Redshift or blue shift of resonance wave...
Absorption Enhancement in thin films
•
In thin film solar cells such as amorphous silicon (a-Si:H) solar cells the
intrins...
ICSEP
19-21 dec. 2012

Goal of the Present work

 To determine the overall contribution on the optical absorption enahnce...
Ag nano particles array for enhancing light absorption within the aSi:H thin film

Plane wave
illumination

Ag MNPs
2R

D
...
ICSEP
19-21 dec. 2012

FDTD simulation span

Simulation Model
PML

PBC

 Periodic Boundary Condition (PBC)
models the per...
ICSEP
19-21 dec. 2012

Results

Fraction of light absorbed (Pabs (λ)) with respect to wavelength (λ)

Figure 1. For the ar...
ICSEP
19-21 dec. 2012

Parameter that makes the difference is
inter particle coupling
ICSEP
19-21 dec. 2012



Interpretations

Increases the surface coverage from 31% to 58% increases the electromagnetic
co...
ICSEP
19-21 dec. 2012

Results
Total Integrated absorption

To comprehend the optical absorption due to AM1.5G solar
radia...
ICSEP
19-21 dec. 2012

Observations

 We observe a second maxima (PST) in PT.
If we consider PT for a wide range of R
fro...
ICSEP
19-21 dec. 2012

Results

Absorption enhancement over the visible spectrum
Absorption enhancement,     

Enhanc...
Role of SiO2 (spacer layer) thickness
SiO2
Optimum Optimum
Total
thickness Radius
Period Integrated
(nm)
(nm)
(nm)
Absorpt...
Choice of metal:
Comparison between Ag, Au and Al

Absorption Enhancement

1.4

1.2

Al
Au
Ag

1.0

0.8

0.6
400

450

500...
ICSEP
19-21 dec. 2012

Conclusion

•

There is significant contribution of quadrupolar mode in optical
absorption.

•

Usi...
Publications:
Jounal publication:
1. Aparajita Mandal and Partha Chaudhuri, Size and period optimization of front
pattered...
ICSEP
19-21 dec. 2012

Thank you for your kind attention
Additional details…..

Scattering cross section ( ) with respect to wavelength of a single Ag
nano particle in air as a fu...
Upcoming SlideShare
Loading in …5
×

Plasmonic assisted optical absorption enhancement in thin films, a theoretical perspective

1,150 views

Published on

absorption enhancement,inter particle coupling,localised surface plasmon,metal nano particles,mie theory,plasmonics,quadrupolar modes,silver,spacer layer, amorphous silicon

Published in: Education, Technology
0 Comments
0 Likes
Statistics
Notes
  • Be the first to comment

  • Be the first to like this

No Downloads
Views
Total views
1,150
On SlideShare
0
From Embeds
0
Number of Embeds
3
Actions
Shares
0
Downloads
69
Comments
0
Likes
0
Embeds 0
No embeds

No notes for slide
  • Why not hexapolar
  • Simulation span defines D
  • Plasmonic assisted optical absorption enhancement in thin films, a theoretical perspective

    1. 1. Plasmonic assisted optical absorption enhancement in thin films a theoretical perspective Aparajita Mandal JRF, department of ERU Indian Association for the Cultivation of Science
    2. 2. ICSEP 19-21 dec. 2012  Outline Plasmonics: • Goal of the present work • Simulation Model • Results and Interpretations • Conclusion
    3. 3. Plasmonics Localized Surface plasmon: The stationary oscillation of conduction electrons confined on a nano sized metal boundary under the excitation of electromagnetic field.
    4. 4. ICSEP 19-21 dec. 2012 Plasmonics Particle size dependence
    5. 5. • Plasmonics: Particle Size dependence Electrostatics + ++ ++ Dipolar mode R<< λ -- - - Phase retardation across the volume R ≈λ - - + + + + -- Electrodynamics Higher order mode
    6. 6. Advantages • Local field enhancement (Light can be confined to a volume which is much smaller the wavelength). • Enhanced light scattering ( eff   g ) • Tunability over the optical properties (such as resonance frequency, forward or backward scattering, bandwidth) of the nano particles by controlling the size, shape and dielectric environment.
    7. 7. ICSEP 19-21 dec. 2012 Mie Theory Overall scattering or absorption cross section σ scat/abs for a single NP as a sum of the contribution from all the normal modes supported by the particles.  scat / abs  scat / abs   n n 1 Where σ n scat/abs is the contribution of the nth normal mode. Theoretically infinite number of plasmon modes is possible…. For very small particles , contribution of only dipolar (DP) mode (n = 1 ) is effective. As particle size increases, higher order modes (e.g. n = 2 corresponds to quadrupole and so on) gradually start to dominate the extinction spectra.
    8. 8. ICSEP 19-21 dec. 2012 Effects of higher order modes on extinction spectra  Higher order modes introduce additional peaks at shorter wavelengths than dipolar peak.
    9. 9. ICSEP 19-21 dec. 2012 • For an array of MNPs Electromagnetic coupling exists between MNPs, strength of which is determined by the interparticle seperation. + + - + - - + Nature of interaction is dependent on polarization of incident light
    10. 10. ICSEP 19-21 dec. 2012 Effect of inter-particle coupling on extinction spectra • Redshift or blue shift of resonance wavelength. • Nature of shift depends on the increase or decrease in the restoring force of oscillating electron cloud. • spectral overlap between different modes.
    11. 11. Absorption Enhancement in thin films • In thin film solar cells such as amorphous silicon (a-Si:H) solar cells the intrinsic layer need to be thin ( 300nm) in order to reduce the light induced degradation. • This thickness restriction results in reduced absorption of the solar spectrum and low short circuit current of such solar cells. • Plasmonics is a promising way of enhancing light absorption within the thin absorber layer.
    12. 12. ICSEP 19-21 dec. 2012 Goal of the Present work  To determine the overall contribution on the optical absorption enahncement within an hydrogenated amorphous silicon film (a-Si:H) of thickness 200nm of front patterned Ag MNPs having size of the order of visible wavelength.  Going beyond dipolar contribution on absorption : Ag MNPs are large enough to support higher order plasmon modes.  To investigate how coupling between the MNPs modifies the higher order modes and thereby influencing the absorption.  Understanding the role of Spacer layer thickness for front patterning.  Usefulness of large MNPs.
    13. 13. Ag nano particles array for enhancing light absorption within the aSi:H thin film Plane wave illumination Ag MNPs 2R D SiO2 a-Si:H Structure used for simulation using Finite Difference Time Domain (FDTD) Method that solves Maxwell’s curl equations of electromagnetism Parameters: R, D, surface coverage, SiO2 thickness, shape and type of metal nano particles (Ag, Au or Al).
    14. 14. ICSEP 19-21 dec. 2012 FDTD simulation span Simulation Model PML PBC  Periodic Boundary Condition (PBC) models the periodicity of the MNPs in X and Y directions. PBC PBC PBC It also takes into account interparticle coupling effect. Plane wave illumination Ag MNPs SiO2 a-Si:H  Perfectly Matched Layer (PML) prevents any non physical reflections from Z direction. PML Schematic of the structure simulated using FDTD method
    15. 15. ICSEP 19-21 dec. 2012 Results Fraction of light absorbed (Pabs (λ)) with respect to wavelength (λ) Figure 1. For the array of Ag nano particles with radii R and constant surface coverage of 31 %. Figure 2. For the array of Ag nano particles with radii R and constant array period of 350 nm. Covergae factor changes from 31 % to 58 %.
    16. 16. ICSEP 19-21 dec. 2012 Parameter that makes the difference is inter particle coupling
    17. 17. ICSEP 19-21 dec. 2012  Interpretations Increases the surface coverage from 31% to 58% increases the electromagnetic coupling between the L-MNPs .  As a result, the distinct DP and QP peak in the scattering spectra combines together resulting in a cooperative spectral property [1] that produces a single and broad spectral absorption peak within the a-Si:H layer.  Redshift in figure 1 is associated with both the effect of changing R and D.
    18. 18. ICSEP 19-21 dec. 2012 Results Total Integrated absorption To comprehend the optical absorption due to AM1.5G solar radiation, we have calculated the total integrated absorption as, P  T 800  I    P   d  abs 400 I (λ) describes the irradiance of AM1.5G at λ.
    19. 19. ICSEP 19-21 dec. 2012 Observations  We observe a second maxima (PST) in PT. If we consider PT for a wide range of R from 40 nm -200 nm, there will be two peaks : One occuring for smaller R that have dipole dominated extinction spectra [2] , another (PST) for larger R supporting higher order modes .  Position of PST with respect to R changes with D. Total integrated absorption PT as a function of Ag nano particle radii for array period (a) 350 nm (b) 380 nm (c) 400 nm (d) 450 nm. PST indicates the second maxima due to higher order modes. r denotes PT in bare a-Si:H (without MNPs) We attribute the occurrence of PST as resulting from the optimum coupling between the higher order modes of L-MNPs depending upon the values of D.
    20. 20. ICSEP 19-21 dec. 2012 Results Absorption enhancement over the visible spectrum Absorption enhancement,      Enhancement throughout broad spectrum Pabs    Pb ( ) Enhancement within narrow wavelengths band ɳ˂1 is represented as black regions
    21. 21. Role of SiO2 (spacer layer) thickness SiO2 Optimum Optimum Total thickness Radius Period Integrated (nm) (nm) (nm) Absorption (Watt m-2) 0 75 400 191.6 2 65 350 201.58 20 65 400 196.14 For nano particles having fixed geometrical cross section, increase in SiO2 layer thickness: • • Increases the effective scattering cross section of the NPs. Decreases the coupling fraction of scattered light into the a-Si:H layer. Therefore, there exists an optimum spacer layer thickness [Table.1]. t =0 t = 2 nm t = 20 nm
    22. 22. Choice of metal: Comparison between Ag, Au and Al Absorption Enhancement 1.4 1.2 Al Au Ag 1.0 0.8 0.6 400 450 500 550 600 650 700 750 wavelength (nm)  Proper choice of metal depending on the absorption enhancement in the desired wavelength range can be made.
    23. 23. ICSEP 19-21 dec. 2012 Conclusion • There is significant contribution of quadrupolar mode in optical absorption. • Using the size characteristics of dipolar and quadrupolar plasmon modes and their dependence on the array period, it is possible to tailor position of absorption peaks. • The enhancement may be tuned to occur either over a broad spectral range or as a narrow band as demanded for the device application. • Aluminum would be a promising candidate in plasmonic solar cell applications as it can provide efficient absorption enhancement in the visible wavelength range.
    24. 24. Publications: Jounal publication: 1. Aparajita Mandal and Partha Chaudhuri, Size and period optimization of front pattered interactiong metal nanoparticles for maximizing absorption of solar radiation in amorphous silicon thin films, J. Opt. 14 (2012) 065001 (6pp). 2. Aparajita Mandal, Partha Chaudhuri, Journal of Renewable and Sustainable Energy 5, 031614, 2013. 3. Aparajita Mandal and Partha Chaudhuri, “Contribution of higher order plasmonic modes on optical absorption enhancement in amorphous silicon thin films”, Volume 300, Pages 77–84, 2013. Conference Proceedings: 1. Aparajita Mandal and Partha Chaudhuri, Simulation of optical absorption enhancement in amorphous silicon using front surface patterning with metal nanostructures, Energy and Eco friendly Materials, December 12-16th, Coimbatore, India, page 67-70, Macmillan Advanced Research Series.
    25. 25. ICSEP 19-21 dec. 2012 Thank you for your kind attention
    26. 26. Additional details….. Scattering cross section ( ) with respect to wavelength of a single Ag nano particle in air as a function of radius . Dipolar (DP), Quadrupolar (QP) and Octupolar (OP) resonances are indicated. Plasmonic contribution in optical absorption within a 200 nm thick aSi:H layer as a function of wavelength for an array of Ag nano particles radii of (a) 135 nm and (b) 65 nm. Peaks in due to the dominating dipolar (DDP) and quadrupolar mode (DQP) is shown.

    ×