4. Efficiency of the light absorption channel via plasmon for various materials

Nanoparticles of gold and silver (sometimes also of copper) are mostly used in plasmon photovoltaics because their surface plasmon resonances are located within the visible light spectrum. These nanoparticles can be deposited on various semiconductor substrates with different material parameters. We list here the appropriate parameters usable for comparison with experiment for various configurations of the plasmon solar cell systems. In order to compare with the experiment, we can estimate the photocurrent in the case of a semiconductor photodiode with the metallically modified photoactive surface. This photocurrent is given by I <sup>0</sup> ¼ ∣e∣N q<sup>0</sup> þ qm A, where N is the number of incident photons and q<sup>0</sup> and qm are the probabilities of single photon absorption in the ordinary photo effect [8] and of single photon absorption mediated by the presence of metallic nanospheres, respectively, as derived in the previous paragraph; <sup>A</sup> <sup>¼</sup> <sup>τ</sup><sup>n</sup> f tn <sup>þ</sup> <sup>τ</sup> p f tp is the amplification factor (τ n pð Þ <sup>f</sup> is the annihilation time of both sign carriers, tn pð Þ is the drive time for carriers [the time of traversing the distance between electrodes]). From the above formulae, it follows that (here I ¼ I <sup>0</sup> qm <sup>¼</sup> <sup>0</sup> , i.e., the photocurrent without metallic modifications),

$$\frac{I'}{I} = 1 + \frac{q\_m}{q\_0} \,' \tag{19}$$

where the ratio qm=q<sup>0</sup> is given by Eq. (18).

qm <sup>¼</sup> <sup>β</sup>C<sup>0</sup>

>>>>:

photo effect can be expressed as follows

qm q0 ¼

experiment in Ref. [14]), ns � 108

for various materials

where <sup>f</sup>ð Þ¼ <sup>ω</sup> <sup>1</sup> ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi ω2 1�ω<sup>2</sup> ð Þ<sup>2</sup>

and <sup>D</sup><sup>0</sup> <sup>¼</sup> <sup>e</sup><sup>2</sup>neE04πa<sup>3</sup>

q0

<sup>C</sup><sup>0</sup> <sup>¼</sup> Nm4=3πa<sup>3</sup>

124 Plasmonics

The ratio, qm

8 >>>><

> βC<sup>0</sup> 128 9

128 <sup>9</sup> <sup>π</sup><sup>2</sup> a3

<sup>þ</sup>4ω2=τ0<sup>2</sup>

4 ffiffiffi 2 <sup>p</sup> <sup>π</sup><sup>2</sup>a<sup>3</sup>βC<sup>0</sup>

8 >>>>>><

>>>>>>:

This ratio turns out to be of order of 104 <sup>β</sup><sup>40</sup>

8π<sup>2</sup>a<sup>2</sup>βC<sup>0</sup> m<sup>∗</sup>

ffiffiffi 2 <sup>p</sup> <sup>π</sup><sup>2</sup>

μ ffiffiffiffiffiffiffiffiffiffi μ∗ nμ<sup>∗</sup> p

<sup>a</sup><sup>2</sup> <sup>μ</sup><sup>3</sup>=<sup>2</sup> m<sup>2</sup>

<sup>m</sup><sup>2</sup> <sup>ħ</sup><sup>ω</sup> � Eg

� � <sup>e</sup><sup>6</sup>n<sup>2</sup>

ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi ħω � Eg q e<sup>6</sup>n<sup>2</sup>

wave is next ruled out from Eq. (17) due to normalization per single photon as in Eq. (13);

p � �<sup>2</sup>

� �ε<sup>2</sup> , for <sup>a</sup><sup>ξ</sup> <sup>≫</sup> <sup>1</sup>:

ħω � Eg

semiconductor layer, which including the phenomenological factor β, and the thickness H (we have confirmed experimentally that the range of the near-field zone exceeds the Mie wavelength), is sufficient to explain the scale of the experimentally observed strong enhancement of absorption rate in semiconductors due to plasmons. The strong enhancement of this transition probability is linked with the allowance of momentum-non-conserved transitions, which is, however, reduced with the radius a growth. The strengthening of the near-field induced interband transitions, in the case of large nanospheres, is, however, still significant as the quenching of oblique interband transitions is partly compensated by � <sup>a</sup><sup>3</sup> growth of the amplitude of dipole plasmon oscillations. The trade-off between these two competing size-dependent factors is responsible for the observed experimental enhancement of light absorption and emission in diode systems mediated by surface plasmons in nanoparticle surface coverings [7, 14–18].

Nanoparticles of gold and silver (sometimes also of copper) are mostly used in plasmon photovoltaics because their surface plasmon resonances are located within the visible light spectrum. These nanoparticles can be deposited on various semiconductor substrates with different material parameters. We list here the appropriate parameters usable for comparison with experiment

ffiffiffiffiffiffiffiffiffiffiffiffi m<sup>∗</sup> nm<sup>∗</sup> p p m<sup>∗</sup>

3μ<sup>3</sup>=<sup>2</sup>m<sup>2</sup> ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi

e<sup>4</sup>n<sup>2</sup> <sup>e</sup>ω<sup>2</sup>f 2 ð Þ ω

p � �<sup>2</sup>

3μm<sup>2</sup> ħω � Eg

4. Efficiency of the light absorption channel via plasmon

eω ħ4 ε3 f 2

eω ħ3 ε3 f 2

<sup>q</sup> corresponds to amplitude factor for driven damped oscillator

<sup>3</sup><sup>m</sup> fð Þ ω (in Eq. (10)); the amplitude of the electric field, E0, in the incident e-m

<sup>V</sup> , V is the volume of the semiconductor, Nm is the number of metallic nanospheres.

, revealing the advantage of the plasmon-mediated photo effect over the ordinary

e<sup>4</sup>n<sup>2</sup> <sup>e</sup>ω<sup>2</sup>f 2 ð Þ ω

<sup>p</sup> <sup>ħ</sup>ε<sup>2</sup> , for <sup>a</sup><sup>ξ</sup> <sup>≪</sup> <sup>1</sup>,

ð Þ ω , for aξ ≪ 1,

(17)

(18)

ð Þ ω , for aξ ≫ 1,

H nm½ � for the surface density of nanoparticles (as in

<sup>=</sup>cm2; note that <sup>C</sup><sup>0</sup> <sup>¼</sup> ns4πa<sup>3</sup>=ð Þ <sup>3</sup><sup>H</sup> , <sup>H</sup> is a thickness of the

q

In Tables 1–3, we list parameters for several semiconductor substrates and for a metallic nanoparticle few materials, which allow for comparison of the ratio qm=q<sup>0</sup> for various material configurations by formula (18).

Formula (18) is exemplified in Figure 1 for Au nanoparticles deposited on Si semiconductor (continuous line)–this reproduces well the experimental behavior (red dashed/dotted) [14]. Both channels of photon absorption resulting in photocurrent in the semiconductor sample are included, the direct ordinary photo effect absorption with probability of transitions given by q<sup>0</sup> and the plasmon-mediated absorption with probability qm, respectively. Note also that


Table 1. Plasmon energies measured in metals.


Table 2. Mie frequency ω<sup>1</sup> to formula (18).


Table 3. Substrate material parameters to formula (18) (<sup>m</sup> <sup>¼</sup> <sup>9</sup>:<sup>1</sup> � <sup>10</sup>�<sup>31</sup> kg, the mass of bare electron; lh–light holes, hh–heavy holes, L–longitudinal, T–transverse).

some additional effects like reflection of the incident photons or destructive interference on metallic net would contribute and it was phenomenologically accounted in the plasmonmediated channel by an experiment-fitted factor β. The collective interference type corrections are rather not strong for the considered low densities of metallic coverings of order of 10<sup>8</sup> =cm2, and nanosphere sizes well lower than the resonant wavelength, though for larger concentrations and larger nanosphere sizes, would play a stronger reducing role (reflecting photons) [6, 19]. The resonance threshold was accounted for the damped resonance envelope function in Eq. (19) including also semiconductor band-gap limit. The relatively high value of qm q0 � 104 <sup>β</sup><sup>40</sup> H nm½ � enables a significant growth of the efficiency of the photoenergy transfer to the semiconductor, mediated by surface plasmons in nanoparticles deposited on the active layer, by increasing β or reducing H (at constant ns). However, because of the fact that an enhancement of β easily induces the overdamped regime of plasmon oscillations, the more prospective would be lowering of H especially convenient in thin film solar cells. The overall behavior of I 0 =Ið Þ¼ ω 1 þ qm=q<sup>0</sup> calculated according to the relation (19), and depicted in Figure 1, agrees quite well with the experimental observations [14], in the position, height and shape of the photocurrent curves for distinct samples (the strongest enhancement is achieved for a ¼ 40 nm, for Au and Si substrate).

blue shifted in comparison to Si and GaAs. Figure 2 reveals an increase in efficiency of the plasmon effect with growth of the value of forbidden gap Eg conserving other parameters not changed. Especially significantly influential material parameter occurs, however, a mass of

Figure 2. Comparison of the effectiveness of the plasmon channel for Si, GaAs and CIGS substrates with the same Au

.

Plasmonic Enhancement of Solar Cells Efficiency: Material Dependence in Semiconductor Metallic Surface Nano…

denominator in the formula (12) for the ordinary photo effect and next the numerator in

and Cu) is presented for two their sizes (a ¼ 50, 25 nm). The blue shift of spectral characteristics for Ag and Cu in comparison to Au is noticeable (cf. also Figure 5) and even more visible for lower radii of nanoparticles due to narrowing of spectral curves (cf. Figure 6). From the comparison in Figures 5 and 6, for Si and CIGS substrates with Au, Ag and Cu nanoparticles

nanoparticles utilize the visible spectrum in the better manner than Ag or Cu ones. The advantage of Au nanoparticles is greater in the case of Si substrate and is reduced for CIGS

Figure 3. Comparison of the effectiveness of the plasmon channel for varying Eg but the same effective masses of

substrates covered with the same Au nanoparticles with radius 50 nm and surface density 108

. In Figure 4, the material comparison of metal material of nanoparticles (Au, Ag

<sup>p</sup> the lower efficiency q<sup>0</sup> of the ordinary photo effect is and higher

p <sup>2</sup>

http://dx.doi.org/10.5772/intechopen.79113

=cm2), one can notice that Au

=cm<sup>2</sup> . , enters the

127

holes, cf. Figure 3, which is also noticeable from Eq. (18). The mass of holes, m<sup>∗</sup>

of size <sup>a</sup> <sup>¼</sup> <sup>50</sup>, 25 nm (at the nanoparticle concentration ns <sup>¼</sup> 108

Eq. (18). The higher mass m<sup>∗</sup>

nanoparticles with radius 50 nm and surface density 108=cm2

the ratio qm

q0

In Figure 2, we present the spectral dependence of the plasmonic efficiency enhancement with respect to substrate change (Si, CIGS and GaAs) for the same Au nanoparticles with radius <sup>a</sup> <sup>¼</sup> 50 nm and the same nanoparticle concentration ns <sup>¼</sup> 108 =cm2. One can note that for the CIGS substrate (copper-indium-gallium-diselenide) the spectral characteristics is narrower and

Figure 1. Spectral dependence of the normalized photocurrent <sup>I</sup> 0 <sup>I</sup> ð Þ λ according to formulae (19) and (18)—Comparison with the experimental data (red) from Ref. [14]: <sup>a</sup> <sup>¼</sup> 25 nm, ns <sup>¼</sup> <sup>6</sup>:<sup>6</sup> � <sup>10</sup><sup>8</sup> <sup>1</sup>=cm2, (center): <sup>a</sup> <sup>¼</sup> 40 nm, ns <sup>¼</sup> <sup>1</sup>:<sup>6</sup> � <sup>10</sup><sup>8</sup> <sup>1</sup>=cm2, (right): <sup>a</sup> <sup>¼</sup> 50 nm, ns <sup>¼</sup> <sup>0</sup>:<sup>8</sup> � <sup>10</sup><sup>8</sup> <sup>1</sup>=cm<sup>2</sup> (<sup>H</sup> <sup>¼</sup> <sup>3</sup>μm).

Plasmonic Enhancement of Solar Cells Efficiency: Material Dependence in Semiconductor Metallic Surface Nano… http://dx.doi.org/10.5772/intechopen.79113 127

some additional effects like reflection of the incident photons or destructive interference on metallic net would contribute and it was phenomenologically accounted in the plasmonmediated channel by an experiment-fitted factor β. The collective interference type corrections are rather not strong for the considered low densities of metallic coverings of order of 10<sup>8</sup>

Table 3. Substrate material parameters to formula (18) (<sup>m</sup> <sup>¼</sup> <sup>9</sup>:<sup>1</sup> � <sup>10</sup>�<sup>31</sup> kg, the mass of bare electron; lh–light holes,

and nanosphere sizes well lower than the resonant wavelength, though for larger concentrations and larger nanosphere sizes, would play a stronger reducing role (reflecting photons) [6, 19]. The resonance threshold was accounted for the damped resonance envelope function in

enables a significant growth of the efficiency of the photoenergy transfer to the semiconductor, mediated by surface plasmons in nanoparticles deposited on the active layer, by increasing β or reducing H (at constant ns). However, because of the fact that an enhancement of β easily induces the overdamped regime of plasmon oscillations, the more prospective would be lowering of H especially convenient in thin film solar cells. The overall behavior of

=Ið Þ¼ ω 1 þ qm=q<sup>0</sup> calculated according to the relation (19), and depicted in Figure 1, agrees quite well with the experimental observations [14], in the position, height and shape of the photocurrent curves for distinct samples (the strongest enhancement is achieved for a ¼ 40 nm,

In Figure 2, we present the spectral dependence of the plasmonic efficiency enhancement with respect to substrate change (Si, CIGS and GaAs) for the same Au nanoparticles with radius

CIGS substrate (copper-indium-gallium-diselenide) the spectral characteristics is narrower and

0

the experimental data (red) from Ref. [14]: <sup>a</sup> <sup>¼</sup> 25 nm, ns <sup>¼</sup> <sup>6</sup>:<sup>6</sup> � <sup>10</sup><sup>8</sup> <sup>1</sup>=cm2, (center): <sup>a</sup> <sup>¼</sup> 40 nm, ns <sup>¼</sup> <sup>1</sup>:<sup>6</sup> � <sup>10</sup><sup>8</sup> <sup>1</sup>=cm2,

<sup>a</sup> <sup>¼</sup> 50 nm and the same nanoparticle concentration ns <sup>¼</sup> 108

Figure 1. Spectral dependence of the normalized photocurrent <sup>I</sup>

(right): <sup>a</sup> <sup>¼</sup> 50 nm, ns <sup>¼</sup> <sup>0</sup>:<sup>8</sup> � <sup>10</sup><sup>8</sup> <sup>1</sup>=cm<sup>2</sup> (<sup>H</sup> <sup>¼</sup> <sup>3</sup>μm).

Eq. (19) including also semiconductor band-gap limit. The relatively high value of qm

<sup>n</sup> m<sup>∗</sup>

Si 0:9 m L[101], 0:19 m T[110] 0:16 m lh, 0:49 m hh 1.12 eV GaAs 0:067 m 0:08 m lh, 0:45 m hh 1.35 eV CIGS 0:09 � 0:13 m 0:72 m 1 � 1:7 eV

I 0

for Au and Si substrate).

Semiconductor m<sup>∗</sup>

126 Plasmonics

hh–heavy holes, L–longitudinal, T–transverse).

=cm2,

� 104 <sup>β</sup><sup>40</sup> H nm½ �

q0

<sup>p</sup> Eg

=cm2. One can note that for the

<sup>I</sup> ð Þ λ according to formulae (19) and (18)—Comparison with

Figure 2. Comparison of the effectiveness of the plasmon channel for Si, GaAs and CIGS substrates with the same Au nanoparticles with radius 50 nm and surface density 108=cm2 .

blue shifted in comparison to Si and GaAs. Figure 2 reveals an increase in efficiency of the plasmon effect with growth of the value of forbidden gap Eg conserving other parameters not changed. Especially significantly influential material parameter occurs, however, a mass of holes, cf. Figure 3, which is also noticeable from Eq. (18). The mass of holes, m<sup>∗</sup> p <sup>2</sup> , enters the denominator in the formula (12) for the ordinary photo effect and next the numerator in Eq. (18). The higher mass m<sup>∗</sup> <sup>p</sup> the lower efficiency q<sup>0</sup> of the ordinary photo effect is and higher the ratio qm q0 . In Figure 4, the material comparison of metal material of nanoparticles (Au, Ag and Cu) is presented for two their sizes (a ¼ 50, 25 nm). The blue shift of spectral characteristics for Ag and Cu in comparison to Au is noticeable (cf. also Figure 5) and even more visible for lower radii of nanoparticles due to narrowing of spectral curves (cf. Figure 6). From the comparison in Figures 5 and 6, for Si and CIGS substrates with Au, Ag and Cu nanoparticles of size <sup>a</sup> <sup>¼</sup> <sup>50</sup>, 25 nm (at the nanoparticle concentration ns <sup>¼</sup> 108 =cm2), one can notice that Au nanoparticles utilize the visible spectrum in the better manner than Ag or Cu ones. The advantage of Au nanoparticles is greater in the case of Si substrate and is reduced for CIGS

Figure 3. Comparison of the effectiveness of the plasmon channel for varying Eg but the same effective masses of substrates covered with the same Au nanoparticles with radius 50 nm and surface density 108 =cm<sup>2</sup> .

Figure 4. Comparison of the effectiveness of the plasmon channel for varying hole mass m<sup>∗</sup> <sup>p</sup> but the same electron mass and Eg of substrates covered with the same Au nanoparticles with radius 50 nm and surface density 108=cm2 .

Figure 5. Comparison of the effectiveness of the plasmon channel for the same substrate Si with Au (red), Ag (blue) and Cu (brown) nanoparticles of the same radius 50 nm and surface density 108=cm<sup>2</sup> .

concentration (from the 5% colloidal solution sputtering over the surface) has been applied to

Figure 6. Comparison of the effectiveness of the plasmon channel for the same substrate Si (upper) and CIGS (lower) with

Plasmonic Enhancement of Solar Cells Efficiency: Material Dependence in Semiconductor Metallic Surface Nano…

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129

, versus the

Au (red), Ag (blue) and Cu (green) nanoparticles of the same radius 50 nm and surface density 108=cm<sup>2</sup>

Worth noting is an agreement of experimentally observed difference in the increase of the efficiency due to the plasmon effect in both cases, of mc-Si and CIGS cells, if one compares the results of application of Au and Ag particles (at the same size of metallic nanoparticles and the same their surface concentration). This behavior agrees with the theoretical study of the material dependence of the plasmon effect, as shown above. From Figures 2–5, we see that for Si substrate Au nanoparticles with radii 50 nm better utilize the solar light spectrum than Ag or Cu particles (cf. Figure 5), and indeed in the experiment (cf. Figure 8) for Au nanoparticles the efficiency growth is ca. 10% larger than for Ag nanoparticles of the same size and concentration on the substrate m-Si solar cell. Interestingly, for the substrate CIGS cell, the effect is weaker and inverted, cf. Figure 9. This also is noticeable from the theoretical modeling—due to different Eg and effective masses of carriers for CIGS with respect to mc-Si. The maxima for efficiency enhancement for Au and Ag mutually shift in such a way that for CIGS Ag nanoparticles a bit better suit to solar light spectrum than Au nanoparticles. However, to analyze these effects in more detail, a measurement of spectral characteristics of all considered structures at varying but

monochromatic illumination uniformly calibrated should be performed.

different samples)—for more detail cf. Ref. [19].

sunlight spectrum on the earth surface.

substrate because the blue shift of Eg in CIGS with respect to Si. In the case of CIGS (especially for large nanoparticles, a ¼ 50 nm), the advantage of Au beyond Ag in overall utilization of sunlight spectrum disappears, whereas is pronounced in the case of Si substrate. Later, we describe an experimental confirmation of this behavior of Si and CIGS substrates, at laboratory sunlight-type illumination by Yamashita DensoYSS-50Aunder AM1.5 [19].

For nanoparticles of gold (Au) and silver (Ag) of size, a ¼ 50 nm, optimized due to formula (18), deposited on the multi-crystalline silicon (mc-Si) and on the copper-indium-galliumdiselenide (CIGS) solar cells, the measured [19] overall increase of cell efficiency attains the level of even 5%. The application of suitable concentration of Au and Ag nanoparticles onto mc-Si solar cells increases their efficiency by 5.6 and 4.8%, respectively [19]. Application of Au and Ag nanoparticles onto surface of CIGS solar cells improves their efficiency by 1.2 and 1.4%, respectively [19]. This is visualized in Figures 7 and 8, where it is compared an increase in solar cell overall efficiency (the ratio of the field beneath the I-V curve for the metallically improved solar cell and the clean solar cell; the same size (50 nm for radius) and the same

Plasmonic Enhancement of Solar Cells Efficiency: Material Dependence in Semiconductor Metallic Surface Nano… http://dx.doi.org/10.5772/intechopen.79113 129

Figure 6. Comparison of the effectiveness of the plasmon channel for the same substrate Si (upper) and CIGS (lower) with Au (red), Ag (blue) and Cu (green) nanoparticles of the same radius 50 nm and surface density 108=cm<sup>2</sup> , versus the sunlight spectrum on the earth surface.

concentration (from the 5% colloidal solution sputtering over the surface) has been applied to different samples)—for more detail cf. Ref. [19].

substrate because the blue shift of Eg in CIGS with respect to Si. In the case of CIGS (especially for large nanoparticles, a ¼ 50 nm), the advantage of Au beyond Ag in overall utilization of sunlight spectrum disappears, whereas is pronounced in the case of Si substrate. Later, we describe an experimental confirmation of this behavior of Si and CIGS substrates, at laboratory

Figure 5. Comparison of the effectiveness of the plasmon channel for the same substrate Si with Au (red), Ag (blue) and

.

<sup>p</sup> but the same electron mass

.

For nanoparticles of gold (Au) and silver (Ag) of size, a ¼ 50 nm, optimized due to formula (18), deposited on the multi-crystalline silicon (mc-Si) and on the copper-indium-galliumdiselenide (CIGS) solar cells, the measured [19] overall increase of cell efficiency attains the level of even 5%. The application of suitable concentration of Au and Ag nanoparticles onto mc-Si solar cells increases their efficiency by 5.6 and 4.8%, respectively [19]. Application of Au and Ag nanoparticles onto surface of CIGS solar cells improves their efficiency by 1.2 and 1.4%, respectively [19]. This is visualized in Figures 7 and 8, where it is compared an increase in solar cell overall efficiency (the ratio of the field beneath the I-V curve for the metallically improved solar cell and the clean solar cell; the same size (50 nm for radius) and the same

sunlight-type illumination by Yamashita DensoYSS-50Aunder AM1.5 [19].

Cu (brown) nanoparticles of the same radius 50 nm and surface density 108=cm<sup>2</sup>

Figure 4. Comparison of the effectiveness of the plasmon channel for varying hole mass m<sup>∗</sup>

128 Plasmonics

and Eg of substrates covered with the same Au nanoparticles with radius 50 nm and surface density 108=cm2

Worth noting is an agreement of experimentally observed difference in the increase of the efficiency due to the plasmon effect in both cases, of mc-Si and CIGS cells, if one compares the results of application of Au and Ag particles (at the same size of metallic nanoparticles and the same their surface concentration). This behavior agrees with the theoretical study of the material dependence of the plasmon effect, as shown above. From Figures 2–5, we see that for Si substrate Au nanoparticles with radii 50 nm better utilize the solar light spectrum than Ag or Cu particles (cf. Figure 5), and indeed in the experiment (cf. Figure 8) for Au nanoparticles the efficiency growth is ca. 10% larger than for Ag nanoparticles of the same size and concentration on the substrate m-Si solar cell. Interestingly, for the substrate CIGS cell, the effect is weaker and inverted, cf. Figure 9. This also is noticeable from the theoretical modeling—due to different Eg and effective masses of carriers for CIGS with respect to mc-Si. The maxima for efficiency enhancement for Au and Ag mutually shift in such a way that for CIGS Ag nanoparticles a bit better suit to solar light spectrum than Au nanoparticles. However, to analyze these effects in more detail, a measurement of spectral characteristics of all considered structures at varying but monochromatic illumination uniformly calibrated should be performed.

Figure 7. Comparison of the effectiveness of the plasmon channel for the same substrate Si (upper) and CIGS (lower) with Au (red), Ag (blue) and Cu (green) nanoparticles of the same radius 25 nm and surface density 108=cm<sup>2</sup> , versus the sunlight spectrum on the earth surface.

5. Conclusion

nanoparticles, (right) by Ag nanoparticles [19].

semiconductor parameters for Si and CIGS.

We have demonstrated by application of the Fermi Golden Rule scheme, that the efficiency of the energy transfer channel between the surface plasmon oscillations in a metallic nanoparticles and a substrate semiconductor depends on parameters of both deposited metallic particles (its radius and material) as well as on semiconductor parameters (energy gap, and effective masses of electron and holes). Found by us formula which generalizes the ordinary photo effect onto the plasmon-mediated one, agrees well with the experimental measurements in laboratory photodiode configuration. The measured ratio of photocurrent in the setup with and without metallic nano-components is compared with the theoretically predicted scenario. The quantitative consistence is obtained both in the shape of the spectral characteristics and in the particle size dependence (as illustrated for Si diode with deposited Au nanoparticles with radii 25, 40 and 50 nm). The qualitative agreement has been achieved also for complete solar cells where the plasmon effect is obscured by other elements of the long series of effects resulting in overall solar cell efficiency beyond only efficiency of the absorption of photons. We have compared the experimental data for multi-crystalline Si solar cell and CIGS (copper-indium-gallium-diselenide) solar cell covered or not with gold and silver nanoparticles with radii of order of 50 nm. The increase of the overall photovoltaic efficiency for metallically modified cells varies between 1.5 (CIGS) and 6% (Si), depending on nanoparticle concentration (for too dense concentration the efficiency drops down). A bit better increase (ca. 10% difference) causes Au nanoparticles for Si cell in comparison to Ag nanoparticles, whereas for CIGS cell, the difference between effect of Ag nanoparticles and Au ones is inverted and strongly reduced. This also agrees qualitatively with theory predictions taken into account differences in Mie frequency in Au and Ag and also different

Figure 9. Comparison of solar cell efficiency due to plasmon modification for the CIGS cell, (left) modified by Au

Plasmonic Enhancement of Solar Cells Efficiency: Material Dependence in Semiconductor Metallic Surface Nano…

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131

Figure 8. Comparison of solar cell efficiency due to plasmon modification for the multi-crystal Si solar cell, (left) modified by Au nanoparticles, (right) by Ag nanoparticles [19].

Plasmonic Enhancement of Solar Cells Efficiency: Material Dependence in Semiconductor Metallic Surface Nano… http://dx.doi.org/10.5772/intechopen.79113 131

Figure 9. Comparison of solar cell efficiency due to plasmon modification for the CIGS cell, (left) modified by Au nanoparticles, (right) by Ag nanoparticles [19].

### 5. Conclusion

Figure 7. Comparison of the effectiveness of the plasmon channel for the same substrate Si (upper) and CIGS (lower) with

Figure 8. Comparison of solar cell efficiency due to plasmon modification for the multi-crystal Si solar cell, (left) modified

, versus the

Au (red), Ag (blue) and Cu (green) nanoparticles of the same radius 25 nm and surface density 108=cm<sup>2</sup>

sunlight spectrum on the earth surface.

130 Plasmonics

by Au nanoparticles, (right) by Ag nanoparticles [19].

We have demonstrated by application of the Fermi Golden Rule scheme, that the efficiency of the energy transfer channel between the surface plasmon oscillations in a metallic nanoparticles and a substrate semiconductor depends on parameters of both deposited metallic particles (its radius and material) as well as on semiconductor parameters (energy gap, and effective masses of electron and holes). Found by us formula which generalizes the ordinary photo effect onto the plasmon-mediated one, agrees well with the experimental measurements in laboratory photodiode configuration. The measured ratio of photocurrent in the setup with and without metallic nano-components is compared with the theoretically predicted scenario. The quantitative consistence is obtained both in the shape of the spectral characteristics and in the particle size dependence (as illustrated for Si diode with deposited Au nanoparticles with radii 25, 40 and 50 nm). The qualitative agreement has been achieved also for complete solar cells where the plasmon effect is obscured by other elements of the long series of effects resulting in overall solar cell efficiency beyond only efficiency of the absorption of photons. We have compared the experimental data for multi-crystalline Si solar cell and CIGS (copper-indium-gallium-diselenide) solar cell covered or not with gold and silver nanoparticles with radii of order of 50 nm. The increase of the overall photovoltaic efficiency for metallically modified cells varies between 1.5 (CIGS) and 6% (Si), depending on nanoparticle concentration (for too dense concentration the efficiency drops down). A bit better increase (ca. 10% difference) causes Au nanoparticles for Si cell in comparison to Ag nanoparticles, whereas for CIGS cell, the difference between effect of Ag nanoparticles and Au ones is inverted and strongly reduced. This also agrees qualitatively with theory predictions taken into account differences in Mie frequency in Au and Ag and also different semiconductor parameters for Si and CIGS.
