Experimental Studies of Plasmonic Nanoparticle Effects on Organic Solar Cells - Organic Solar Cells: Materials and Device Physics - page 223

decreases. When Au NPs concentration reaches 6 wt%, almost no photovoltaic
effect is observed (PCE *0.01 %).
It should be noted that in the study [ 35 ], Au NPs have been capped with PEG.
In order to investigate the effects of PEG on device performances, the PEG-only
OSCs were fabricated in which only PEG was incorporated into the polymer blend.
PEG concentration in the mixed solution is *0.08 mg/ml which equals that of the
PEG in 0.5 wt% Au NPs mixed with polymer blend solution. The PEG-only OSC
shows similar J-V characteristics and PCE (*1.67 %) to that of the device
without PEG incorporation (PCE *1.64 %). Therefore, PEG itself is not likely to
have pronounced effects on device performances.
8.3.2 LSPR Effects
The degree of contributions of LSPR effect can be observed from the absorption
spectrum of the active layer incorporated with various Au NPs concentrations,
while the physical understanding can be obtained from theoretical analyzing the
absorption of OSCs as shown in Fig. 8.11 . The theoretical near-field profile of
electric field (Fig. 8.11 b) shows very strong field strength laterally distributed
along the active layer which can enhance the light absorption by the polymer blend
for generating carriers. It is noteworthy that when Au NPs incorporated into PE-
DOT:PSS layer (i.e., the layer adjacent to the active layer), the light absorption in
the active layer is not clearly enhanced due to the lateral distribution feature of the
strong LSPR near field along the PEDOT:PSS layer rather than a vertical distri-
bution into the active layer as described in our another work [ 18 ].
Fig. 8.11 a Experimental and theoretical (inset) absorbance enhancement factor of the active
layer with different amount of Au NPs. b Theoretical near-field distribution around an Au NP in
the active layer [ 35 ]