136
turns the device color to black. Using this structure, impressive EQE values of
>80% was achieved over the spectrum from 400 nm to 800 nm, as shown in Fig. 4c,
due to the presence of nanocone array [21]. In fact, the maximum light absorption
is achieved by nanocone at the front side and minimum PV losses is achieved at the
back side of the device, resulting in 30.7% enhancement of J SC for textured device.
The photovoltaic curve of the corresponding device showed significant improvement of the J sc for the textured device as compared to the planar one without losing
any V oc . The PCE for the nanocone-based device was 13.7%, which was much
higher than the planar one with 10.9%, indicating the advantage of the nanostructures [21].
This mechanism is dominant for nanostructures such as nanocone and nanospike
with a gradient of the effective refractive index, which can work as broad-band and
omnidirectional AR layer [21, 28]. This mechanism is also observed for uniform
diameter of nanostructures such as nanowell, nanowire, and nanopillar. In these
cases, the diameter and length play a significant role in optical absorption due to
plasmonic resonance which is another effective light management scheme [29].
Plasmonic effect is normally applied in a solar cell device using metallic nanoparticles. These nanoparticles showed surface plasmons, which is corresponded to the
excitations of the electrons at a metal/dielectric interface [29, 30]. By proper designing of the morphology and geometry of these metallodielectric structures, light can
be focused on absorber layer of the device, resulting in higher absorption. In fact,
both plasmonic effects from the localized surface plasmon in the metallic nanoparticles and the surface plasmon polaritons (SPPs) at the interface of metal/semiconductor are beneficial for increasing the absorption [29–32]. Plasmonic effect can
reduce the thickness of the absorber layer while maintaining the same optical
absorption in three ways, as shown in Fig. 4e. In the first approach, the metallic
nanoparticles are employed as scattering elements for subwavelengths to trap the
plane waves from the sunlight into the absorber layer. In the second way, they can
be employed as subwavelength antennas, where the plasmonic field is coupled with
the absorber layer to increase the absorption. In the third approach, a corrugated
layer of metallic film is formed at the back of the device, which can couple the plane
waves of lights into the SPP modes at the metal/absorber interface and conduct the
modes into the absorber layer [29]. Then, the scattered light obtains an angular
spread in the absorber layer and increases the optical path length, resulting in light
trapping. In fact, the light beams will pass many times in the absorber layer, enhancing the effective path length [30, 31]. Additionally, the size and shape of metallic
nanoparticles also play critical roles for improving the incoupling efficiency [32].
Figure 4f shows that the smaller size of metallic nanoparticles (close to the semiconductor layer) can couple larger amount of light into the absorber layer due to the
improved near-field coupling.
M. M. Tavakoli
turns the device color to black. Using this structure, impressive EQE values of
>80% was achieved over the spectrum from 400 nm to 800 nm, as shown in Fig. 4c,
due to the presence of nanocone array [21]. In fact, the maximum light absorption
is achieved by nanocone at the front side and minimum PV losses is achieved at the
back side of the device, resulting in 30.7% enhancement of J SC for textured device.
The photovoltaic curve of the corresponding device showed significant improvement of the J sc for the textured device as compared to the planar one without losing
any V oc . The PCE for the nanocone-based device was 13.7%, which was much
higher than the planar one with 10.9%, indicating the advantage of the nanostructures [21].
This mechanism is dominant for nanostructures such as nanocone and nanospike
with a gradient of the effective refractive index, which can work as broad-band and
omnidirectional AR layer [21, 28]. This mechanism is also observed for uniform
diameter of nanostructures such as nanowell, nanowire, and nanopillar. In these
cases, the diameter and length play a significant role in optical absorption due to
plasmonic resonance which is another effective light management scheme [29].
Plasmonic effect is normally applied in a solar cell device using metallic nanoparticles. These nanoparticles showed surface plasmons, which is corresponded to the
excitations of the electrons at a metal/dielectric interface [29, 30]. By proper designing of the morphology and geometry of these metallodielectric structures, light can
be focused on absorber layer of the device, resulting in higher absorption. In fact,
both plasmonic effects from the localized surface plasmon in the metallic nanoparticles and the surface plasmon polaritons (SPPs) at the interface of metal/semiconductor are beneficial for increasing the absorption [29–32]. Plasmonic effect can
reduce the thickness of the absorber layer while maintaining the same optical
absorption in three ways, as shown in Fig. 4e. In the first approach, the metallic
nanoparticles are employed as scattering elements for subwavelengths to trap the
plane waves from the sunlight into the absorber layer. In the second way, they can
be employed as subwavelength antennas, where the plasmonic field is coupled with
the absorber layer to increase the absorption. In the third approach, a corrugated
layer of metallic film is formed at the back of the device, which can couple the plane
waves of lights into the SPP modes at the metal/absorber interface and conduct the
modes into the absorber layer [29]. Then, the scattered light obtains an angular
spread in the absorber layer and increases the optical path length, resulting in light
trapping. In fact, the light beams will pass many times in the absorber layer, enhancing the effective path length [30, 31]. Additionally, the size and shape of metallic
nanoparticles also play critical roles for improving the incoupling efficiency [32].
Figure 4f shows that the smaller size of metallic nanoparticles (close to the semiconductor layer) can couple larger amount of light into the absorber layer due to the
improved near-field coupling.
M. M. Tavakoli