Ternary
Bulk Heterojunction Solar Cells: Addition of Soluble NIR Dyes for
Photocurrent Generation beyond 800 nm
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Abstract
The
incorporation of a <i>tert</i>-butyl-functionalized silicon
2,3-naphthalocyanine bis(trihexylsilyloxide) dye molecule as a third
component in a ternary blend bulk heterojunction (BHJ) organic solar
cell containing P3HT (donor) and PC<sub>60</sub>BM (acceptor) results
in increased NIR absorption. This absorption yields an increase of
up to 40% in the short-circuit current and up to 19% in the power
conversion efficiency (PCE) in photovoltaic devices. Two-dimensional
grazing incidence wide-angle X-ray scattering (2-D GIWAXS) experiments
show that compared to the unfunctionalized dye the <i>tert</i>-butyl functionalization enables an increase in the volume fraction
of the dye molecule that can be incorporated before the device performance
decreases. Quantum efficiency and absorption spectra also indicate
that, at dye concentrations above about 8 wt %, there is an approximately
30 nm red shift in the main silicon naphthalocyanine absorption peak,
allowing further dye addition to contribute to added photocurrent.
This peak shift is not observed in blends with unfunctionalized dye
molecules, however. This simple approach of using ternary blends may
be generally applicable for use in other unoptimized BHJ systems towards
increasing PCEs beyond current levels. Furthermore, this may offer
a new approach towards OPVs that absorb NIR photons without having
to design, synthesize, and purify complicated donor–acceptor
polymers