Experimental Studies of Plasmonic Nanoparticle Effects on Organic Solar Cells - Organic Solar Cells: Materials and Device Physics - page 224

Fig. 8.12 IPCE of OSCs
incorporated with different
concentrations of Au NPs
[ 35 ]
The theoretical and experimental absorption enhancement of the active layer
(PFSDCN:PCBM) indicates that LSPR for the case of low Au NPs concentration
mixed active layer exists at around 650 nm which is different from that of Au NPs
(*520 nm) in chloroform/chlorobenzene (1:1 v/v ratio) due to the change of the
surrounding optical environment. Moreover, when the spacing between Au NPs
reduces (i.e., higher Au NPs concentration), the theoretical and experimental
results show that the resonance strength increases and slightly red shifts. Conse-
quently, the theoretical results are in agreement with the experimental results. The
results demonstrate and explain the features of LSPR excited by Au NPs incor-
porated into OSCs active layer.
The light absorption can be enhanced experimentally by over 100 % at the
resonance region when Au NPs concentration increases to 6 wt% as shown in
Fig. 8.11 a. However, the effects of LSPR alone cannot completely interpret the
overall observed phenomena of OSCs. For example, low Au NPs concentration
can benefit OSC performances. Continuously enhanced light absorption is
obtained with the increase of Au NPs concentration due to the stronger LSPR.
However, when Au NPs concentration [0.5 wt%, deterioration of device perfor-
mances is obtained, which is quite unexpected in the viewpoint of LSPR effects.
This can be further illustrated from IPCE characteristics as shown in Fig. 8.12 .
When the Au NPs concentration reaches 6 wt%, a large absorption enhancement
factor is obtained (Fig. 8.11 a), but IPCE decreases to almost zero. Therefore,
besides LSPR effects, the effects of Au NPs on OSC electrical properties need to
be investigated for understanding the results.
8.3.3 Effects on Carrier Mobility
Generally, electron and hole mobilities are the important factors and should be
high enough to guarantee large carrier hopping rate, to avoid carrier recombination