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M. B. Ross et al.
Fig. 3.4 Method for calculating solar integrated N3 dye absorption enhancement factor C EF .
The solar spectrum and N3 dye absorption spectra are normalized according to Eq. 3.5, and then
multiplied by the surface-average field, the result is then integrated (purple hatched area, bottom
panel). For this example (30 nm radius silver sphere coated with 10 nm of AgO and 2 nm amorphous
TiO 2 ), C EF = 12.9
result is an integrated cross-section enhancement of C EF = 12.9. Silver is readily
oxidized at ambient conditions and thus this layer of oxide must be considered as it
changes the dielectric environment of the particle. Figure 3.5 shows the results of the
same analysis for a wide range of silver particle sizes and AgO coating thicknesses.
The AgO has a dielectric constant of 6.25, and so increasing the thickness causes a
dramatic red-shift in the plasmon resonance as is expected (Eq. 3.2). For example, for
the r Ag = 5 nm case, when no AgO is present, the LSPR peaks at 366 nm, whereas for
20 nm of AgO it peaks at 550 nm. For a particle of this size, the field enhancement
drops off rapidly with increased oxide layer thickness. When the silver radius is
increased to 30 nm, this tunability causes the resonance to cross the maximum dye
absorption cross-section (around 400 nm), and the reduction in the field enhancement
is not as severe as in the small particle case. These factors combine to form a region
of optimum geometry when the silver radius is 30 nm and the oxide coating is about
10 nm. Although this enhances the dye absorption by a factor of almost 13, the
enhancement covers only a small fraction of the solar spectrum.
3.3 Enhancing the Solar Spectrum
A majority of the energy in the solar spectrum resides in the spectral range 300 nm–
1,750 nm. Capturing the largest possible fraction of this spectrum is essential for
any solar application. The tunability of the absorption efficiency of metal nanoparticles with size, shape and composition is particularly important for dye-based cells;
M. B. Ross et al.
Fig. 3.4 Method for calculating solar integrated N3 dye absorption enhancement factor C EF .
The solar spectrum and N3 dye absorption spectra are normalized according to Eq. 3.5, and then
multiplied by the surface-average field, the result is then integrated (purple hatched area, bottom
panel). For this example (30 nm radius silver sphere coated with 10 nm of AgO and 2 nm amorphous
TiO 2 ), C EF = 12.9
result is an integrated cross-section enhancement of C EF = 12.9. Silver is readily
oxidized at ambient conditions and thus this layer of oxide must be considered as it
changes the dielectric environment of the particle. Figure 3.5 shows the results of the
same analysis for a wide range of silver particle sizes and AgO coating thicknesses.
The AgO has a dielectric constant of 6.25, and so increasing the thickness causes a
dramatic red-shift in the plasmon resonance as is expected (Eq. 3.2). For example, for
the r Ag = 5 nm case, when no AgO is present, the LSPR peaks at 366 nm, whereas for
20 nm of AgO it peaks at 550 nm. For a particle of this size, the field enhancement
drops off rapidly with increased oxide layer thickness. When the silver radius is
increased to 30 nm, this tunability causes the resonance to cross the maximum dye
absorption cross-section (around 400 nm), and the reduction in the field enhancement
is not as severe as in the small particle case. These factors combine to form a region
of optimum geometry when the silver radius is 30 nm and the oxide coating is about
10 nm. Although this enhances the dye absorption by a factor of almost 13, the
enhancement covers only a small fraction of the solar spectrum.
3.3 Enhancing the Solar Spectrum
A majority of the energy in the solar spectrum resides in the spectral range 300 nm–
1,750 nm. Capturing the largest possible fraction of this spectrum is essential for
any solar application. The tunability of the absorption efficiency of metal nanoparticles with size, shape and composition is particularly important for dye-based cells;