(714g) Plasmonic Polymer Solar Cells with Spectrally Tuned Au/SiO2 Core/Shell Nanorods Incorporated in Active Layers

Octadecyl tri-methoxysilane
(OTMS) functionalized Au/SiO₂ core/shell nanorods
were incorporated into the active layers of two different polymer bulk heterojunction (BHJ) systems:  a broad band gap polymer (poly(3-hexylthiophene)(P3HT):[6,6]-phenyl-C61-butyric
acid methyl ester(PCB60M)) and a low band gap polymer poly{2,6-4,8-di(5-ethylhexylthienyl)benzo[1,2-b;3,4-b]dithiophene-alt-5-dibutyloctyl-3,6-bis(5-bromothiophen-2-yl)
pyrrolo[3,4-c]pyrrole-1,4-dione} (PBDTT-DPP):PC₆₀BM.
The extinction peaks of the Au nanorod scattering
centers was tuned to match the band edge of the two polymers by controlling
their aspect ratio. For the P3HT:PC₆₀BM system with a band edge
around 700 nm, the addition of the core/shell nanorods
of an aspect ratio 1:2.5 (resonant frequency peak is at around λ=650nm),
resulted in 8% improvement in short circuit current (J_sc);
for the low band gap polymer system PBDTT-DPP: PC₆₀BM with band edge
around 850 nm, we tuned the resonant frequency to near-infrared region by
increasing the aspect ratio to 1:4 (resonant frequency peak is at around
λ=800nm),  the addition of the core/shell
nanorods resulted in 18% improvement in short circuit
current (J_sc). The Jsc
enhancement was consistent with external quantum efficiency (EQE) measurements
and the EQE improvement factor matched the absorption resonance spectrum of
Au/SiO₂nanorods in both systems. This
work will instruct us on how to utilize and manipulate plasmon
resonance of metallic nanoparticles to improve device
efficiency in different polymer solar cell systems.

(a.) Photographic image Au nanosphere
and 6 Au nanorod solutions, extinction spectra of Au nanosphere and 6 nanorod
solutions and absorption spectra of two OPV polymers: PC3HT:PC_6oBM
and PBDTT-DPP:PCC₆₀BM  (B.)
TEM images of bare and silica coated Au nanorods with
650nm and 810nm resonances. The red shift in the peak plasmon
resonance is due to the silica shell layer

(a) J-V measurement of PBTDD-DPP: PC₆₀BM BHJ
(Bulk heterojunction) solar cells with and without
Au/SiO₂nanorods.  (b) External quantum efficiency(EQE)
measurement of PBTDD-DPP:PC₆₀BM BHJ (Bulk heterojunction)
solar cells with and without Au/SiO₂nanorods.
(c) EQE enhancement factor v.s. the plasmon resonance spectrum of Au/SiO₂nanorods (AR~1:4).