Oxide-encapsulated silver NPs embedded in polymer for improved optical absorption
Enhanced electric fields associated with surface plasmons can enhance light absorption in the surrounding medium that the plasmonic materials are embedded in. The exploitation of these unique properties in organic solar cells is well documented. Organic solar cells suffer from inherently low phot...
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Format: | Theses and Dissertations |
Language: | English |
Published: |
2017
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Online Access: | http://hdl.handle.net/10356/72666 |
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Institution: | Nanyang Technological University |
Language: | English |
Summary: | Enhanced electric fields associated with surface plasmons can enhance light absorption in
the surrounding medium that the plasmonic materials are embedded in. The exploitation
of these unique properties in organic solar cells is well documented. Organic solar cells
suffer from inherently low photo current and surface plasmons have the ability to
overcome this drawback by improving absorption in the semiconducting photoactive
layer. As surface plasmons manifest in the immediate vicinity of the plasmonic
nanostructures, their placement in the polymeric active layer (or at least in close
proximity to the active layer) is preferred. As the nanostructures are usually metallic in
nature, embedding them in the semiconducting layer may introduce recombination sites.
This can be circumvented by introducing a thin continuous insulating shell around the
nanostructures. An insulating encapsulation layer helps in isolating nanostructures from
the polymer layer, hence, mitigating' charge recombination.
In this thesis, the effect on optical enhancement in a polymer by embedding 50 nm Ag
nanoparticles (NPs) encapsulated with various oxides is investigated. The focus will be
placed on the use of aluminum oxide (Ab03), hafnium oxide (Hf02), molybdenum oxide
(Mo03) and silicon oxide (Si02). Modelling studies reveal that, at silver (Ag) NP
resonance, optical enhancement in poly(3-hexythiophene ):phenyl-C61-butyric acid
methyl ester (P3HT:PCBM) depends primarily on the position of peak extinction cross
section relative to the polymer absorption. Photoinduced absorption (PIA) studies show
an increased polaron yield when Ag NPs are protected with a sheath of Ab03. In fact, an
optimal Ab03 thickness of 3 - 5 nm exists to generate maximum polaron concentration.
At this range, absorption enhancement within the polymer film by the plasmonic electric
field and the spatial separation of charge carriers from recombination centers are
balanced. Absorption gains/losses in the photoactive layer are examined by calculating
with reference to AM 1.5G solar spectrum. Through the additional use of simulation
models, it is divulged that overall absorption in the polymer can be improved by
incorporating oxide-encapsulated Ag NPs. Assuming a continuous shell is sufficient in
mitigating charge recombination, a 2 nm thickness, regardless of the choice of oxide, should be enough to induce optical enhancement in the polymer with respect to a control
P3HT:PCBM. |
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