Synthesis and characterization of squaric acid based NIR dyes for their application towards dye-sensitized solar cells

Synthesis of novel cyan-colored sensitizing dyes bearing squaric acid core and 2,3,3-trimethyl-indole as terminal moieties has been conducted in order to fabricate dye-sensitized solar cells based on nanoporous TiO2. It has been found that position of –COOH functionality utilized for anchoring with TiO2 surface has a marked effect on solar cell performance. Carboxylic acid group directly substituted to indole ring gave about 5-fold higher conversion efficiency as compared to the dye when it was substituted in alkyl chain of the indole ring. Efficiency has been found to be hampered due to aggregation and enhancement in the efficiency was observed when dyes were used with chenodeoxycholic acid (CDCA). Using CDCA and long alkyl substituent at the N-position of indole ring to prevent aggregation and enhanced TiO2 surface passivation, respectively, has achieved a solar conversion efficiency of 3.15% with a short circuit current density of 7.26 mA/cm2, an open circuit voltage of 0.64 V and a fill factor of 0.68 for SQ-5 under standard AM 1.5 solar irradiation.