Panchromatic Sensitizer for Dye-Sensitized Solar Cells: Unsymmetrical Squaraine Dyes Incorporating Benzodithiophene π-Spacer with Alkyl Chains to Extend Conjugation, Control the Dye Assembly on TiO₂, and Retard Charge Recombination

Abstract

Metal-free near-infrared (NIR) active unsymmetrical squaraine dyes, RSQ1 and RSQ2, with benzodithiophene (BDT) π-spacer and cyanoacrylic acid acceptor were synthesized by utilizing palladium catalyzed direct (hetero)arylation reaction. Methyl and 2-ethylhexyl groups were strategically placed at the BDT unit for RSQ1 and RSQ2, respectively, to investigate the effect of alkylated π-spacer on dye aggregation on the TiO surface and recombination reactions at TiO/dye/electrolyte interface. These dyes have strong absorption (ε > 10 M cm) in near-infrared (NIR) region and exhibit similar optical and electrochemical properties as they have same conjugated framework. RSQ2 performed better than RSQ1 owing to its higher open-circuit voltage (V) and fill factor (ff) in spite of having comparable short-circuit current density (J). The panchromatic incident photon-to-current conversion efficiency (IPCE) response was also observed for both the dyes. RSQ2 showed power conversion efficiency (PCE) of 6.72% with short-circuit current density (J) of 18.53 mA/cm, open circuit voltage (V) of 0.538 V, and fill factor (ff) of 67.4%, without any coadsorbent. Attenuation of the charge recombination for RSQ2 was revealed by electrochemical impedance analysis (EIS) and open-circuit potential decay transients (OCVD), which attributes to its higher V and ff in comparison to RSQ1.

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

“…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.…”

Near‐Infrared‐Absorbing Metal‐Free Organic, Porphyrin, and Phthalocyanine Sensitizers for Panchromatic Dye‐Sensitized Solar Cells

“…RSQ2 also utilizes a core‐symmetric structure with indoline building blocks and a benzodithiophene (BDT)–CAA conjugated π‐bridge‐acceptor on one indoline group. This dye exhibits a good IPCE response across the visible/NIR spectrum with an IPCE onset of 775 nm ( J SC of 18.8 mA cm −2 , PCE of 6.8 %) . Shi et al.…”

“…This dye exhibits ag ood IPCE response across the visible/NIR spectrum with an IPCE onset of 775 nm (J SC of 18.8 mA cm À2 ,P CE of 6.8 %). [52] Shi et al examined as implified derivativeo fR SQ2 with at hiophene in place of the BDT p-bridge( YR6). [53] Devices based on YR6 show an IPCE response with a7 80 nm onset across ab road range of wavelengths to yield aPCE of 6.7 %.…”

Indenoquinaldine‐Based Unsymmetrical Squaraine Dyes for Near‐Infrared Absorption: Investigating the Steric and Electronic Effects in Dye‐Sensitized Solar Cells

“…[11a, 17] There are severals uccessful DSSCs based on squaraine dyes that absorb in the far-red region, however,o nly af ew of them have as pectral response over 800 nm (Figure1). The extension of indole-based coresymmetric squarained yes by using a p spacer,a si nY R6 [18] and RSQ2, [19] leads to good incident photon-to-current efficiency (IPCE) in the NIR region (onset at 775-780nm) with power conversion efficiencies (h)o f6 .7 and 6.8 %, respectively.T he core-dissymmetric squarained ye JK-217, assembled by using thiophenyl, pyrrolyl, andi ndoliumg roups,e xhibits panchromatic light harvesting up to 850 nm to yield an efficiency of 5.5 %. [20] (Detailed explanation of the squaraine dye classification is provided in Scheme S1 in the Supporting Information.)…”