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TitleLight trapping in thin-film silicon solar cells via plasmonic metal nanoparticles
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Page 1

Light trapping in thin-film silicon solar cells via

plasmonic metal nanoparticles

by

Ryan J. Veenkamp, B.Sc. Engineering

A thesis submitted to the

Faculty of Graduate and Postdoctoral Affairs

in partial fulfillment of the requirements for the degree of

Master of Applied Science in Electrical and Computer Engineering

Ottawa-Carleton Institute for Electrical and Computer Engineering

Department of Electronics

Carleton University

Ottawa, Ontario

September, 2014

� Copyright

Ryan J. Veenkamp, 2014

Page 2

The undersigned hereby recommends to the

Faculty of Graduate and Postdoctoral Affairs

acceptance of the thesis

Light trapping in thin-film silicon solar cells via plasmonic

metal nanoparticles

submitted by Ryan J. Veenkamp, B.Sc. Engineering

in partial fulfillment of the requirements for the degree of

Master of Applied Science in Electrical and Computer Engineering

Professor Winnie N. Ye, Thesis Supervisor

Professor Niall Tait, Chair,
Department of Electrical and Computer Engineering

Ottawa-Carleton Institute for Electrical and Computer Engineering

Department of Electronics

Carleton University

September, 2014

ii

Page 64

CHAPTER 4. THEORETICAL DESIGN OF PLASMONIC SOLAR CELL 50

density of conduction electrons, resulting in an extremely negative �m which is de-

sirable for the forward scattering configuration [33]. Whether or not the forward

scattered light contributes to an increase, or reduction, generated photocurrent de-

pends on the phase difference between the light transmitted across the a-Si interface,

and that scattered by the MNPs [53]. Lim et al. [18] showed that below the LSPR

wavelength, a phase shift in the polarizability of the MNPs causes the transmitted

and scattered light to destructively interfere, resulting in a reduction in light absorp-

tion. Correspondingly, at wavelengths longer than the plasmon resonance light un-

dergoes constructive interference leading to enhancements in light absorption. Since

Al LSPRs lie in the UV region, the light scattered by Al MNPs must undergo con-

structive interference over the majority of the solar spectrum. In addition, Tsai et

al. [53] demonstrated that Al MNPs reduce the phase difference in the transmitted

and scattered light compared with Ag, thus leading to strong enhancements in both

the VIS and near-IR regions, as opposed to just the near-IR for Ag particles.

Fig. 4.7 shows the results of 3D FDTD simulations for a simple model of a-Si

as the substrate and 25nm of SiO2 as the dielectric spacer layer. The results of the

simulations have been calibrated to the AM1.5G spectrum in order to determine the

exact behaviour of the MNPs under solar radiation, as in a practical application.

Nanocubes of either material significantly outperform the traditional spherical MNP

shape in terms ofQscat at longer wavelengths, and come close to matching nanospheres

at the shorter wavelengths where solar radiation is most intense. In Fig. 4.7a the

change of material from Ag to Al has a drastic effect on the scattering cross-sections of

the MNPs. Despite the fact that Ag cubes appear to have a greater overall scattering

cross-section when compared directly against the power in the solar spectrum, it is

important to note that the scattering cross-section does not give the full picture in

Page 65

CHAPTER 4. THEORETICAL DESIGN OF PLASMONIC SOLAR CELL 51

Figure 4.7: (a) Normalized scattering cross-sections (Qscat). (b) Fraction of incident
radiation forward scattered into the substrate (Fsubs). (c) Radiative efficiency
of the particles (Nrad). (d) Normalized absorption cross sections (Qabs). The
spacer thickness is set to 25nm and all quantities are calibrated to the power
available in the AM1.5G spectrum at each wavelength.

terms of increasing the amount of light trapped and absorbed in a thin-film solar

cell application. Scattering can be forwards, or backwards, with the latter being

detrimental to cell performance.

Page 128

APPENDIX B. FABRICATION PROCESS FLOW SHEET 114

ITO

9. Deposit 20nm ITO: Semi-
core PVD

Mask 1

UV

10. Liquid HMDS then
positive photoresist
(LOR10B and S1811)
spin coat to define
active cell areas

11. Develop photoresist

12. Etch ITO in Aqua regia
(20s) then remove re-
sist in acetone plus Mi-
croposit Remover 1165

13. Spin coat 180nm PMMA
for e-beam, write
nanocube array then
deposit 80nm Al and
metal lift-off

Mask 1

UV

14. Spin coat photoresist
(LOR10B and S1811)
for top contact mask,
expose

15. Develop resist then
deposit 30nm
Ti/300nm Ag

Page 129

APPENDIX B. FABRICATION PROCESS FLOW SHEET 115

16. Lift-off resist

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