3 Plasmonically Enhanced Dye-Sensitized Solar Cells
135
sitions, copper and gold are poor plasmonic materials in the wavelength range of
300–550 nm; silver is poor below about 350 nm. This suggests that a combination
of silver, gold, and aluminum particles of various sizes could allow for LSPRs from
the UV to the NIR whilst minimizing the interference of interband transitions.
In light of recent methods to cap metal nanoparticles with protective layers, it is
clear that silver is the optimum choice for plasmon enhanced DSSCs. Local surface
plasmon resonances can be excited on silver nanostructures over a majority of the
solar spectrum.
3.3.2 Shape
The variety of shapes available via recent wet chemistry synthetic methods is large
and includes spheres [24], dielectric core-metallic shell particles [25], rods [26–30],
cubes [31, 32], concave cubes [33], octahedra [31], hollow octahedra [34], rhombic
dodecahedra [35], disks [36, 37], triangular prisms [38] and hollow triangular prisms
[39] to name but a few. Of these myriad shapes, only a small fraction have been
incorporated into DSSC devices. Here we will discuss the general properties of these
shapes as they apply to DSSCs and review current progress in incorporating these
structures into DSSCs.
3.3.3 Polarization-Independent Resonances
Spheres, core-shell particles, and, to some extent, cubes exhibit polarizationindependent resonances because of their high symmetries. This is ideal for DSSCs, as
the particles can be readily combined with the semiconductor and deposited onto the
conducting oxide with no regard for the orientation of the nanoparticles in the structure. Lower symmetry structures, such as rods and prisms, have polarization- and
orientation- dependent resonances and care must be taken to optimize the deposition
mechanics to ensure that the long axis of the structures is perpendicular to the incident
sunlight. The inclusion of spherical metal nanoparticles has so far been the dominant
method to investigate the effect of plasmons on the photovoltage and photocurrent
of DSSCs. A summary of DSSC device setups presented in the literature is shown
in Fig. 3.7.
The first example of plasmonically enhanced DSSCs in the literature was in 1997,
where it was shown that 0.3 and 1 % by volume of silver spheres could increase the
photocurrent in a Rose bengal dye-sensitized TiO 2 cell. Here the majority of the
photocurrent comes from direct electron injection from the silver into the TiO 2 (type
A cell, Fig. 3.7) [40]. The same cell showed a decrease in photocurrent upon inclusion
of 3 % by volume gold spheres. This was explained by noting that a majority of the
photocurrent in the silver case arose from UV in the irradiation source, where gold
exhibits interband transitions.
135
sitions, copper and gold are poor plasmonic materials in the wavelength range of
300–550 nm; silver is poor below about 350 nm. This suggests that a combination
of silver, gold, and aluminum particles of various sizes could allow for LSPRs from
the UV to the NIR whilst minimizing the interference of interband transitions.
In light of recent methods to cap metal nanoparticles with protective layers, it is
clear that silver is the optimum choice for plasmon enhanced DSSCs. Local surface
plasmon resonances can be excited on silver nanostructures over a majority of the
solar spectrum.
3.3.2 Shape
The variety of shapes available via recent wet chemistry synthetic methods is large
and includes spheres [24], dielectric core-metallic shell particles [25], rods [26–30],
cubes [31, 32], concave cubes [33], octahedra [31], hollow octahedra [34], rhombic
dodecahedra [35], disks [36, 37], triangular prisms [38] and hollow triangular prisms
[39] to name but a few. Of these myriad shapes, only a small fraction have been
incorporated into DSSC devices. Here we will discuss the general properties of these
shapes as they apply to DSSCs and review current progress in incorporating these
structures into DSSCs.
3.3.3 Polarization-Independent Resonances
Spheres, core-shell particles, and, to some extent, cubes exhibit polarizationindependent resonances because of their high symmetries. This is ideal for DSSCs, as
the particles can be readily combined with the semiconductor and deposited onto the
conducting oxide with no regard for the orientation of the nanoparticles in the structure. Lower symmetry structures, such as rods and prisms, have polarization- and
orientation- dependent resonances and care must be taken to optimize the deposition
mechanics to ensure that the long axis of the structures is perpendicular to the incident
sunlight. The inclusion of spherical metal nanoparticles has so far been the dominant
method to investigate the effect of plasmons on the photovoltage and photocurrent
of DSSCs. A summary of DSSC device setups presented in the literature is shown
in Fig. 3.7.
The first example of plasmonically enhanced DSSCs in the literature was in 1997,
where it was shown that 0.3 and 1 % by volume of silver spheres could increase the
photocurrent in a Rose bengal dye-sensitized TiO 2 cell. Here the majority of the
photocurrent comes from direct electron injection from the silver into the TiO 2 (type
A cell, Fig. 3.7) [40]. The same cell showed a decrease in photocurrent upon inclusion
of 3 % by volume gold spheres. This was explained by noting that a majority of the
photocurrent in the silver case arose from UV in the irradiation source, where gold
exhibits interband transitions.