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Orthogonally Functionalized Donor/Acceptor Homo- and Heterodimeric Dyes for Dye-Sensitized Solar Cells: An Approach to Introduce Panchromaticity and Control the Charge Recombination
journal contribution
posted on 2017-09-12, 00:00 authored by Manik
Chandra Sil, Vediappan Sudhakar, Munavvar Fairoos Mele Kavungathodi, Vellimalai Punitharasu, Jayaraj NithyanandhanOrganic dyes possessing conjugated
π-framework forms closely
packed monolayers on photoanode in dye-sensitized solar cell (DSSC),
because of the limitation to control the orientation and the extend
of intermolecular π–π interaction, self-aggregation
of dyes leads to reduced cell performance. In this report, a series
of homodimeric (D1-D1 and D2-D2) and heterodimeric (D1-D2 and D2-D4) donor/acceptor (D/A) dyes containing spiroBiProDOT
π-spacer were designed and synthesized by utilizing Pd-catalyzed
direct arylation reaction and correlates the device performance with
monomeric dyes (D1 and D2). Both the thiophenes (π-spacer)
of spiroBiProDOT were functionalized with same or different donor
groups which led to homodimeric and heterodimeric chromophores in
a single sensitizer. The homodimeric spiro-dye D1-D1 showed
higher power conversion efficiency (PCE), of 7.6% with a Voc and Jsc of 0.672 V and
16.16 mA/cm2, respectively. On the other hand, the monomeric D1 exhibited a PCE of 3.2% (Voc of 0.64 V and Jsc of 7.2 mA/cm2), which is lower by 2.4 fold compared to
dimeric analogue. The spiro-unit provides flexibility between the
incorporated chromophores to orient on TiO2 due to four
sp3-centers, which arrest the molecular motions after chemisorption.
This study shows a new molecular approach to incorporate two chromophores
in the dimeric dye possessing complementary absorption characteristics
toward panchromatic absorption. The attenuated charge recombination
at TiO2/Dye/redox couple interface in case of D1-D1, owing to better passivation of TiO2 surface, was elucidated
through impedance analysis. The FT-IR spectrum of D1-D1 adsorbed
on TiO2 film indicated both the carboxylic units were involved
in chemisorption which makes strong coupling between dye and TiO2.