Experimental Studies of Plasmonic Nanoparticle Effects on Organic Solar Cells - Organic Solar Cells: Materials and Device Physics - page 220

generation, leading to a lower J sc and FF. On the other hand, the previously
investigated hole collection improvement is advantageous to J sc and FF. The
competition between the two effects contributes to the trend in PCE variation as
shown Table 8.1 : as Au NPs are added to PEDOT:PSS, the surface roughness
increases, creating a larger PEDOT:PSS/P3HT:PCBM interface area. Therefore,
more holes can be collected at the anode, leading to enhancements in J sc , FF and
PCE. However, the increased roughness also affects P3HT:PCBM networking and
reduces exciton quenching. When the Au NPs concentration increases further from
0.32 toward 1.92 %, the negative effects of reduced exciton quenching outweigh
the positive effects of improved hole collection, resulting in the reduction of PCE
as shown in Table 8.1 and thus PCE peaks at 0.32 wt%.
8.2.6 Section Summary
The incorporation of Au NPs into the PEDOT:PSS layer of an OSCs offers *13 %
improvement in PCE in robust material system of P3HT:PCBM, mainly due to
improvements in J sc and FF. The experimental and theoretical studies showed that
absorption enhancements are minimal, and this is explained by the lateral distri-
bution of the strong near field of NPs. The study of PEDOT:PSS morphology
reveals that Au NP incorporation will cause the surface roughness of PEDOT:PSS
to increase, leading to more efficient hole collection. Also, the resistance of PE-
DOT:PSS reduces upon incorporation of NPs. On the other hand, PL measure-
ments indicate that exciton quenching is reduced due to the change in internal
networking of the active layer. The combination of these electrical effects explains
the trend of PCE reported in the work [ 18 ].
8.3 Electrical and Optical Properties of Organic Solar Cells
with Au Nanoparticles Doped into the Active Layer
With our previous section showing that performance improvement of OSCs
incorporated with Au NPs in the PEDOT:PSS layer is not due to LSPR effects, we
would like to discuss the OSC performance improvement mechanisms when NPs
are doped in a different layer and understanding the conditions in which LSPR
effects can be utilized in OSCs. We noticed that previous studies have commonly
used the metallic NPs as an interfacial layer on ITO coated glass substrates or a
dopant of buffer layers such as PEDOT:PSS [ 6 - 9 ]. OSCs with the incorporation of
metallic NPs into the active layer, however, have received limited detailed
investigation. [ 12 , 15 , 34 ] Therefore, the study for further understanding both
optical and electrical properties is highly desirable for OSCs with metallic NPs
incorporated into the active layer.