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A Step Toward Efficient Panchromatic Multi-Chromophoric Sensitizers for Dye Sensitized Solar Cells
Panchromatic
dyes with absorption profiles extending into the near-infrared
are of interest to researchers in the field of dye sensitized solar
cells (DSSCs), as they offer potential access to a wide energy range
of photons necessary to enhance solar to electric power conversion
efficiencies (PCEs). In this report, a porphyrin with a Soret band
absorbing at high energy is combined with a squaraine absorbing at
low energy via an acetylene linker to form a bichromophoric sensitizer
with molar extinctions on the order of 10<sup>5</sup> M<sup>–1</sup> cm<sup>–1</sup> and an incident photon-to-current efficiency
(IPCE) onset of ∼850 nm. Various bulky substituents were installed
on both the porphyrin and squaraine moieties, and conjugation was
increased with π-bridge spacers to achieve a PCE of 7.6%, which
is up to 15% higher than a comparable squaraine-only dye. For the
most part, charge injection dynamics indicate slower charge injection
rates and lower injection quantum yields for these bichromophoric
sensitizers compared to nonporphyrin squaraine-based DSSC sensitizers.
Nevertheless, higher PCE was observed for most porphyrin-containing
dyes due largely to increased panchromaticity