Fused Fluorenylindolenine-Donor-Based Unsymmetrical Squaraine Dyes for Dye-Sensitized Solar Cells

Abstract

A series of four unsymmetrical squaraine dyes, XSQ1-4, were synthesized using a fused fluorenylindolenine-based donor unit for dye-sensitized solar cells (DSSCs). The fused structure of fluorenylindolenine helped in moving the absorption toward the near-infrared (NIR) region, and the two sp-C centers available on this donor were utilized to incorporate out-of-plane alkyl chains in opposite directions to control the dye-dye interactions on the TiO surface. High extinction coefficient (ε ≥ 10 M cm) for absorbing NIR photons and suitable highest occupied molecular orbital and lowest unoccupied molecular orbital energy levels with respect to the conduction band of TiO and electrolyte for charge injection and dye regeneration processes, respectively, make these dyes potential sensitizers for DSSCs. Introduction of branched alkyl groups in the π-framework helped in controlling dye aggregation to reduce exciton quenching and assisted in TiO surface passivation to avoid the charge recombination process. Furthermore, having a naphthyl group on the indole part of the anchoring group containing segment helped to red-shift the absorption spectrum of dyes 15 nm toward the NIR region (XSQ3-4). Among all of the dyes under investigation, XSQ2 gave the best photovoltaic performance, having a short-circuit current density ( J) of 13.99 mA cm, open-circuit voltage ( V) of 0.66 V, and a fill factor (ff) of 0.71, with a device performance (η) of 6.57%. Electrochemical impedance spectroscopy revealed higher electron lifetime on TiO for XSQ2, which helps to avoid the charge recombination process.

Modular TiO2‐Squaraine Dyes/Electrolyte Interface for Dye‐Sensitized Solar Cells with Cobalt Electrolyte

“…The large differences in RE between the squaraine dyes are may be due to TiO 2 ‐dye/electrolyte/counter electrode interfacial compatibility. Furthermore, selected squaraine dyes showed comparatively high regeneration efficiency compared to D‐π‐A dye with cobalt‐electrolyte at high light intensity, which is may be due to the zwitterionic structures of squaraine dyes, and showed their compatibility with cobalt electrolyte [42] …”

“…Furthermore, selected squaraine dyes showed comparatively high regeneration efficiency compared to D-π-A dye with cobaltelectrolyte at high light intensity, which is may be due to the zwitterionic structures of squaraine dyes, and showed their compatibility with cobalt electrolyte. [42] Electrochemical impedance spectroscopy (EIS) Devices fabricated for ASQ4, SQS4 and XSQ2 dyes with cobalt electrolyte along with different counter electrodes have been used for the EIS characterization. EIS studies were carried out in dark experimental conditions by applying different potentials is provided in Figure S11, S12, [45] whereas, EIS parameters with cobalt-based electrolytes for ASQ4, SQS4 and XSQ2 dyes at 0.60 V applied potential is provided in Figure 5, Figure S13 and Table 2.…”

“…[34,40] Sensitizers wrapped with alkyl or alkyl-glycolic chains form a monolayer on the semiconducting metal oxide surface which modulates the accessibility of electrolytes around the photoanode by providing a different level of passivation. [14,41,42] Here, to modulate the TiO 2 -Dye/ Electrolyte interface which is compatible with different electro-lytes is investigated and donor-acceptor-donor (D-A-D) dyes wrapped with alkyl groups XSQ2 [42] (multiple hydrophobic alkyl groups) SQS4 [14] (with N-dodecyl) and alkyl-glycolic chains ASQ4 [41] (with N-glycolic) have been used as sensitizers (due to their impressive IPCE response by photocurrent generation from aggregated structures beside the contribution from the monomeric dyes) for comparative DSSC studies with cobaltbased electrolytes [6] along with the Pt-foil and PEDOT [43] counter electrodes. Structures, UV-vis spectra, and HOMO-LUMO level diagram of NIR-light active squaraine dyes with redox-potential of electrolyte are provided in Figure 1.…”

Solvent-Regulated Coupling of 2-Alkynylbenzaldehydes with Cyclic Amines: Selective Synthesis of Fused N-Heterocycles and Functionalized Naphthalene Derivatives

“…Fused N-heterocycles are attracting more attention because of their crucial roles in materials and pharmaceuticals . Due to their unique photochemical or electrochemical properties, some of them have been used as luminescent or semiconductor materials .…”

“…Fused N-heterocycles are attracting more attention because of their crucial roles in materials and pharmaceuticals . Due to their unique photochemical or electrochemical properties, some of them have been used as luminescent or semiconductor materials . In addition, fused N-heterocycles are essential building blocks of various bioactive derivatives, which display in vivo potent analgesic activity or have a significant effect on the treatment of Alzheimer’s disease, SiHa human tumor, etc.…”