Experimental Studies of Plasmonic Nanoparticle Effects on Organic Solar Cells - Organic Solar Cells: Materials and Device Physics - page 216

Fig. 8.5 Theoretical electric
field profile in the
PEDOT:PSS:Au NPs/
P3HT:PCBM OSCs [ 18 ]

IPCE spectrum. Comparing devices with or without Au NPs in Fig. 8.4 b, it can be
observed that the IPCE shows a wideband improvement from *400 to 650 nm. It
therefore can be concluded that plasmonic effects does not play a major role in
improving PCE and electrical effects have to be accounted for.
It should be noted that in the measurement of light absorption shown in
Fig. 8.4 a, the absorption of the PEDOT:PSS layer (with or without Au NPs) has
been deduced as they will absorb light. Therefore, the absorption spectrum rep-
resents light harvesting within the active layer only, which is important for
understanding the plasmonic effects on device performances. The insignificant
change

in absorption spectra is a direct evidence that light absorption in

P3HT:PCBM is unaffected by the incorporation of Au NPs.

8.2.4 Effects of Au NPs on PEDOT:PSS

The morphology changes of the PEDOT:PSS:Au NP layer can be observed from
AFM images on a PEDOT:PSS:Au NP film for different NP concentrations as
shown in Fig. 8.6 . Upon increasing Au NP concentration, an obvious change can
be observed in surface morphology of the PEDOT:PSS film, with an increase in
roughness of *5 and *40 % for 0.32 and 0.64 wt% Au NPs, respectively. It has
been reported that increasing anode surface roughness will increase the interface
area between the anode and active layer, providing shorter routes for holes to