128
M. B. Ross et al.
Fig. 3.2 Comparison of
carrier paths in DSSCs
without(left) and with (right)
plasmonic nanoparticle
inclusions
with the length of the oxide layer. The further an electron has to travel, the more likely
it is to encounter an oxidized dye and be lost. Each electron that does not reach the
Pt electrode can be considered a wasted photon absorption event. Thus, plasmonic
nanoparticles can lead to lower recombination frequencies via shorter path lengths
in the cell. This can also allow the use of cheaper materials with shorter carrier mean
free paths [11]. Solar conversion efficiencies could increase with diminished material
needs in terms of both scarcity and cost. DSSCs would become easier to implement
on larger scales as they became more economically feasible.
3.2 Plasmon Enhanced Dye-Sensitized Solar Cells
Localized surface plasmon resonances (LSPRs) are characteristic excitations of the
conduction electrons in small metal nanoparticles. They are seen when a, the dimension of the particle, is less than the excitation wavelength, when a < ε. Photons
travelling in media with a positive dielectric constant (λ d > 0) couple with LSPRs
with varying efficiencies based on the nanoparticle shape, size and the relationship
between the medium dielectric constant and the dielectric function of the metal
(λ m (π) = λ r (π) + iλ i (π) ) [12]. The coupling efficiency between photons and the
LSPR is described by the absorption and scattering cross-sections (C abs and C sca respectively) of the nanoparticles. The values of C abs and C sca can be many times larger
than the geometric cross-section of the nanoparticle, indicating in the case of C abs
that the electric field in and around the nanoparticle can be many times the strength
of the incident field. This strong localization of electromagnetic energy around metal
particles is of primary importance to increasing the absorption cross-section of dyes.
In the following, we will discuss the mechanism of enhanced dye absorption due
to LSPRs: including ways to enhance dye absorption over the solar spectrum by
utilizing nanoparticles of various shapes, mitigating Ohmic losses in the metal due
to surface plasmon excitation, and coupling of the particle electromagnetic fields
with the dye.
M. B. Ross et al.
Fig. 3.2 Comparison of
carrier paths in DSSCs
without(left) and with (right)
plasmonic nanoparticle
inclusions
with the length of the oxide layer. The further an electron has to travel, the more likely
it is to encounter an oxidized dye and be lost. Each electron that does not reach the
Pt electrode can be considered a wasted photon absorption event. Thus, plasmonic
nanoparticles can lead to lower recombination frequencies via shorter path lengths
in the cell. This can also allow the use of cheaper materials with shorter carrier mean
free paths [11]. Solar conversion efficiencies could increase with diminished material
needs in terms of both scarcity and cost. DSSCs would become easier to implement
on larger scales as they became more economically feasible.
3.2 Plasmon Enhanced Dye-Sensitized Solar Cells
Localized surface plasmon resonances (LSPRs) are characteristic excitations of the
conduction electrons in small metal nanoparticles. They are seen when a, the dimension of the particle, is less than the excitation wavelength, when a < ε. Photons
travelling in media with a positive dielectric constant (λ d > 0) couple with LSPRs
with varying efficiencies based on the nanoparticle shape, size and the relationship
between the medium dielectric constant and the dielectric function of the metal
(λ m (π) = λ r (π) + iλ i (π) ) [12]. The coupling efficiency between photons and the
LSPR is described by the absorption and scattering cross-sections (C abs and C sca respectively) of the nanoparticles. The values of C abs and C sca can be many times larger
than the geometric cross-section of the nanoparticle, indicating in the case of C abs
that the electric field in and around the nanoparticle can be many times the strength
of the incident field. This strong localization of electromagnetic energy around metal
particles is of primary importance to increasing the absorption cross-section of dyes.
In the following, we will discuss the mechanism of enhanced dye absorption due
to LSPRs: including ways to enhance dye absorption over the solar spectrum by
utilizing nanoparticles of various shapes, mitigating Ohmic losses in the metal due
to surface plasmon excitation, and coupling of the particle electromagnetic fields
with the dye.