Design, Synthesis and Photophysical Characterization of Multifunctional Far‐red Squaraine Dyes for Dye‐Sensitized Solar Cells

Novel far‐red sensitive symmetrical squaraine dyes aiming towards multifunctional properties such as control of dye aggregation, promotion of molecular self‐assembly and introduction of electrolyte function by alkyl chain terminal modification were designed. Newly designed dye without terminal modification as reference (SQ‐5) along with iodine (SQ‐77) and imidazole (SQ‐79) alkyl terminal‐modified dyes were successfully synthesized, characterized, and subjected to detailed photophysical investigations. Iodine terminal modification (SQ‐77) led to enhanced molar extinction coefficient, dye aggregation, dye loading and binding strength on the TiO2 surface, which was found by just the opposite after the imidazole (SQ‐79) terminal modification. Demonstration of nearly similar photovoltaic performance by SQ‐77 and SQ‐79 in the absence of iodine and chenodeoxycholic acid validates their multi‐functional role as electrolyte function and dye aggregation prevention, respectively, in addition to their main role as photosensitizer. DSSCs fabricated with SQ‐5 as a sensitizer showed efficient far‐red to NIR photo‐sensitization and photon harvesting with short‐circuit current density, open‐circuit voltage and fill factor of 11.98 mA/cm2, 0.61 V, and 0.57, respectively leading to a photoconversion efficiency of 4.2 % under simulated solar irradiation.This article is protected by copyright. All rights reserved.