Orthogonally Functionalized Donor/Acceptor Homo- and Heterodimeric Dyes for Dye-Sensitized Solar Cells: An Approach to Introduce Panchromaticity and Control the Charge Recombination

Abstract

Organic 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 (D-D and D-D) and heterodimeric (D-D and D-D) 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 (D and D). 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 D-D showed higher power conversion efficiency (PCE), of 7.6% with a V and J of 0.672 V and 16.16 mA/cm, respectively. On the other hand, the monomeric D exhibited a PCE of 3.2% (V of 0.64 V and J of 7.2 mA/cm), which is lower by 2.4 fold compared to dimeric analogue. The spiro-unit provides flexibility between the incorporated chromophores to orient on TiO due to four sp-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 TiO/Dye/redox couple interface in case of D-D, owing to better passivation of TiO surface, was elucidated through impedance analysis. The FT-IR spectrum of D-D adsorbed on TiO film indicated both the carboxylic units were involved in chemisorption which makes strong coupling between dye and TiO.

Homo‐ and Heterodimeric Dyes for Dye‐Sensitized Solar Cells: Panchromatic Light Absorption and Modulated Open Circuit Potential

“…After addition of 3 mM of CDCA the efficiency was increased up to 3.2 % with J sc of 7.5 mA/cm 2 and V oc of 0.635 V. Further, the IPCE profile of both D 1 ‐D sq , and the mixture of D sq ‐D sq , D 1 ‐D 1 and D sq , D 1 were looking almost with same features. Further, it has been observed that the V oc of dye mixture of D 1 ‐D 1 and D sq ‐D sq is 0.674 V, which is very close to the independent V oc of D 1 ‐D 1 (0.673 V) and 74 mV higher than that of D sq ‐D sq . Similar trends also have been observed for mixture of D 1 and D sq dyes.…”

“…Solid‐state studies inferred that SpiroBiProDOT derivatives showed different conformations depending upon the substitution present in the moiety which helps to provide different orientation between the dyes that were functionalized with this spacer . Formylation of spiroBiProDOT under POCl 3 /DMF reaction conditions provided the corresponding dialdehyde 6 in good yield . The bromoindolium derivative 1 was condensed with the semisquaric acid 2 by azeotropic distillation of water employing a Dean−Stark apparatus to afford bromo‐functionalized squaraine precursor 3 in moderate yield(Scheme ).…”

“…Reagents and solvents were procured from Aldrich and TCI chemicals and used as such. Precursors 1 , 2 , 6 , 9 , and 10 were synthesized by known procedures. All oxygen‐ and moisture‐sensitive reactions were performed under nitrogen atmosphere.…”

“…Donor dyes ( D 1 ‐D 1 and D 1 ) are configured with D‐ π ‐A units with strong absorption in the visible region. On the other hand, acceptor dyes were ( D sq ‐D sq and D sq ) showing prominent absorption at the far‐red region.Device study of D 1 ‐D 1 and D 1 and their applications as sensitizers were reported . From UV/Vis and fluorescence spectroscopy, the spectral overlap between the absorption of acceptor ( D sq ‐D sq and D sq ) dyes and emission of donor ( D 1 ‐D 1 and D 1 ) dyes established the possibility of resonance energy transfer process in solution state.…”

Cause, Regulation and Utilization of Dye Aggregation in Dye-Sensitized Solar Cells

“…With respect to the corresponding non-spiro-linked parent compounds, spiro compounds have higher solubility, improved morphological stability in the solid-state and a reduced tendency to form aggregates [ 121 , 122 ]. The homodimeric spiro dye 32 showed higher PCE of 7.6% (see Table 1 ), which is 2.4 times the monomeric form, and the spiro linker offers the dye better flexibility [ 84 ].…”