Experimental Studies of Plasmonic Nanoparticle Effects on Organic Solar Cells - Organic Solar Cells: Materials and Device Physics - page 211

are commonly incorporated in-side an OSC, their effects on the electrical prop-
erties of OSCs are likely equally important as optical properties. Previous reports
have studied optical effects of the NPs, while the impact of NPs on the electrical
properties of OSCs is still unclear. The understanding on the electrical properties
of OSCs is important for optimizing the plasmonic OSCs and open new applica-
tions of plasmonic nanostructures.
In this chapter, detailed studies in the device mechanisms of OSCs will be
described when NPs are incorporated into various positions through experiment
and theoretical simulations. The objectives are (1) clarify the extent that LSPR
improves absorption in active layer; (2) describe the difference in the role of LSPR
effects when NPs are incorporated into the hole collection layer or active layer; (3)
study the device mechanisms, apart from optical effects, that will be changed when
NPs are incorporated; and (4) describe the large efficiency improvements in OSCs
by incorporation of NPs in all organic layers.
8.2 Electrical and Optical Properties of Organic Solar Cells
with Au Nanoparticles Doped into the PEDOT:PSS Layer
Considering the origin of performance improvement after addition of NPs, the
effects of doping the poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate)
(PEDOT:PSS) layer of a OSC with Au NPs have been reported [ 36 ]. In the report,
monofunctional poly(ethylene glycol) (PEG)-capped Au NPs with average
diameter of 18 nm are doped into the PEDOT:PSS hole collection layer of an
optimized OSC with P3HT:PCBM as the active layer, leading to *13 % peak
PCE improvement. The effect of PEG capping on Au NPs has also been investi-
gated from a device fabrication perspective. Together with theoretical simulations
which are discussed in Chap. 7 [ 16 ], the effects of Au NPs on the optical and
electrical properties of OSCs have been studied. The results show that the com-
petition between improved hole collection at the PEDOT:PSS/active layer inter-
face and reduced exciton quenching, at donor/acceptor junctions, instead of the
LSPR effect, are major contributors to the measured PCE variation.
8.2.1 Performances of the Au NP Devices
The current density (J) versus voltage (V) characteristics of devices with structure
ITO/PEDOT:PSS(with PEG-capped Au NPs)/P3HT:PCBM/LiF(1 nm)/Al(100 nm)
incorporating various Au NP concentrations in PEDOT:PSS layer is shown in
Fig. 8.1 and the device characteristics are summarized in Table 8.1 .
It is shown that increasing Au NPs concentration in PEDOT:PSS improves PCE
of our OSCs, peaking at 0.32 wt% with PCE of 3.51 % which corresponds to