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

In the present study, we introduce a new plan to boost the charge transfer between squaraine sensitizers and the conduction band of TiO2 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 TiO2 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 TiO2. Also, the relatively longer alkyl chain present in SQIND-1 would lower the aggregation of the dye on the TiO2 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 TiO2 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/cm2, 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.