2 research outputs found
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
Near-Infrared Asymmetrical Squaraine Sensitizers for Highly Efficient Dye Sensitized Solar Cells: The Effect of π‑Bridges and Anchoring Groups on Solar Cell Performance
Conventional squaraine
dyes exhibit an intense absorption band
in the red region of the solar spectrum and with appropriate design
can also have high energy absorption as well, making them interesting
building blocks toward achieving panchromatic dyes for dye sensitized
solar cell (DSSC) applications. In this report, eight squaraine dyes
with thiophene, 4-hexyl-4<i>H</i>-dithienoÂ[3,2-<i>b</i>:2′,3′-<i>d</i>]Âpyrrole, dithienoÂ[3,2-<i>b</i>:2′,3′-<i>d</i>]Âthiophene, and
4,4-bisÂ(2-ethylhexyl)-4<i>H</i>-siloloÂ[3,2-<i>b</i>:4,5-<i>b</i>′]Âdithiophene (DTS) Ï€-bridges
with cyanoacetic acid (CA) and cyanophosphonic acid (PA) acceptor/anchoring
groups are synthesized to extend the squaraine absorption into the
450–550 nm region and to provide different spatial arrangements
of solubilizing groups. Squaraines with CA anchoring groups have higher
power conversion efficiencies compared to their PA analogs, with the
highest being 8.9% for the DTS-based dye, which is among the highest
reported in the literature for squaraine dyes. This is due to high
short circuit currents (<i>J</i><sub>SC</sub>) and increased
open circuit voltages (<i>V</i><sub>OC</sub>). Dyes with
PA anchoring groups exhibited lower <i>J</i><sub>SC</sub> resulting from decreased charge injection efficiency, as determined
by femtosecond transient absorption spectroscopy. This study suggests
that out-of-plane bulky substituents may increase DSSC performance
not only by increasing <i>J</i><sub>SC</sub> through decreased
aggregation but also by increasing <i>V</i><sub>OC</sub> through decreased TiO<sub>2</sub>/electrolyte recombination