Fused heterocycles possessing novel metal-free organic dyes for dye-sensitized solar cells

Abstract

A series of fused heterocycles possessing novel metal free organic dyes viz., CPTAA-1, CPTAA-2, TCPTAA-1 and TCPTAA-2 has been designed and synthesized as sensitizers for dye-sensitized solar cells (DSSCs). Explorations on the relationship between the dye structures, photophysical/electrochemical properties, and DSSC performances have been described. The dyes CPTAA-1 and CPTAA-2 possess superior absorption maxima both in dichloromethane and adsorbed on TiO2 compared to TCPTAA-1 and TCPTAA-2. All the dyes display more positive ground state oxidation potential than the redox potential of I−/I3− electrolyte and more negative excited state oxidation potential than the conduction band edge of the semiconductor. Incorporation of additional carbazole scaffolds in CPTAA-1 and CPTAA-2 culminated with reduced photocurrent density, probably, due to poor interaction between the bulky dyes (TCPTAA-1 and TCPTAA-2) and semiconductor. Of the DSSCs fabricated, the one with CPTAA-1 displayed the highest incident photon-to-current conversion efficiency (IPCE). The DSSC device with CPTAA-1 exhibited high power conversion efficiency (η = 4.38 ± 0.3%) compared to the others with an open circuit voltage (VOC) of 648 ± 0.4 mV, short circuit current density (JSC) of 10.03 ± 0.2 mA cm−2, and fill factor (ff) of 0.66 ± 0.002 under simulated AM 1.5G irradiation (100 mW/cm−2).