Synthesis and characterization of new squaraine dyes with bis-pendent carboxylic groups for dye-sensitized solar cells

Abstract In the present study, we introduce a new plan to boost the charge transfer between squaraine sensitizers and the conduction band of TiO 2 by increasing the anchoring number. Two new symmetric squaraine sensitizers (SQIND-1 and SQIND-2) derived from indoline and having pendant bis-COOH as anchor groups to inject the electron into the TiO 2 nanoparticles were tested as DSSC. The theoretical calculations and absorbance results showed that the electron density of LUMO of SQIND-1 is delocalized in the whole carboxylic group resulting in strong electronic interaction between SQIND-1 sensitizer and the conducting band of TiO 2 . Also, the relatively longer alkyl chain present in SQIND-1 would lower the aggregation of the dye on the TiO 2 surface compared to SQIND-2. Hence, the SQIND-1 sensitized exhibit better photovoltaic performance. Dye-sensitized solar cell base fabricated in SQIND-1 was on TiO 2 with the long wavelength and NIR region up to 750 nm of the spectrum and showed higher noteworthy performance properties, such as energy conversion efficiency (η) of 6.2% (AM 1.5 G), a short-circuit photocurrent density of 6.64 mA/cm 2 , an open-circuit photovoltage of 0.53, a fill factor of 0.72 and an incident photon-to-current conversion efficiency of 45% at 668 nm.