Environmental Engineering Reference
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7.4.3 Hybrid Plasmonic System
We propose a novel optical design of OSC with a hybrid plasmonic system, which
comprises a plasmonic cavity coupled with a dielectric core-metal shell (DC-MS)
nanosphere. It has been investigated that optical absorption of the active polymer
material has a 4-fold increase. With the help of rigorous VIE method presented in
Sect. 7.3.3 , we unveil the fundamental physics of the significant enhancement,
which mainly attributes to the coupling of symmetric surface wave modes supported
by the cavity resonator. We further demonstrate that the optical enhancement
strongly depends on the decay length of surface plasmon waves penetrated into the
active layer. Moreover, coherent interaction between the cavity and the DC-MS
nanosphere is definitely confirmed by our theoretical model. A distribution of
polarization charges on the surface of the cavity indicates a bonding and antibonding
coupling modes [ 42 ] in the hybrid plasmonic system. The work introduces a new
hybrid plasmonic cavity device structure to enhance the optical absorption of
organic photovoltaics with detailed physical explanations.
Figure 7.9 shows the schematic pattern of a heterojunction OSC. A hybrid
plasmonic system, which comprises a plasmonic cavity coupled with a dielectric
core-metal shell nanosphere, is employed for improving the optical absorption of
the active polymer material. A transparent spacer is inserted to avoid local shunt
and extract carriers. The incident light is propagated from the spacer to the active
layer at the vertical incident angle with an E-field polarized along the x direction.
Figure 7.10 a shows the real and imaginary parts of the refractive index of the
active material.
First, various nanosphere concentrators (excluding the plasmonic cavity) are
systematically and comparatively observed. These nanospheres include a dielectric
sphere, a metal sphere, a metal core-dielectric shell (MC-DS) sphere, and a
dielectric core-metal shell (DC-MS) sphere. The scattering cross-section (SCS) of
the nanospheres can be obtained from the generalized reflection coefficients of the
spherically layered media [ 59 , 79 , 80 ]
X
1
r s ¼ 2p
K 3
2
2
R TM
þ R TE
ð 2m þ 1 Þ
3 ; 2 ð m Þ
3 ; 2 ð m Þ
ð 7 : 41 Þ
m ¼ 1
where 1, 2, and 3 denote the core, shell, and active layers as shown in Fig. 7.9 ,
respectively, m is the order of the modified spherical Bessel (Hankel) functions,
and R TM
3 ; 2
and R TE
3 ; 2 are the generalized reflection coefficients of the TM and TE
spherical waves in the layer 3 reflected by the layer 2. For small spherical particles,
the leading term (m ¼ 1) of R TM
3 ; 2 determines the value of the SCS. The generalized
reflection coefficient can be written as a recursive equation
i 1 ; i R TM
i ; i 1 þ T TM
i 1 ; i 2 T TM
i ; i 1
R TM
i ; i 1 ¼ R TM
ð 7 : 42 Þ
i 1 ; i R TM
1 R TM
i 1 ; i 2
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