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

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• 作者：Rajesh Bisht ; Munavvar Fairoos M. K. ; Ambarish Kumar Singh ; Jayaraj Nithyanandhan
• 刊名：Journal of Organic Chemistry
• 出版年：2017
• 出版时间：February 17, 2017
• 年：2017
• 卷：82
• 期：4
• 页码：1920-1930
• 全文大小：700K
• ISSN：1520-6904

文摘

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 TiO₂ surface and recombination reactions at TiO₂/dye/electrolyte interface. These dyes have strong absorption (ε > 10⁵ M^–1 cm^–1) 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_oc) and fill factor (ff) in spite of having comparable short-circuit current density (J_sc). 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_sc) of 18.53 mA/cm², open circuit voltage (V_oc) 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_oc and ff in comparison to RSQ1.