Fine tuning the absorption and photovoltaic properties of benzothiadiazole dyes by donor-acceptor interaction alternation via methyl position

Abstract

Four isomeric organic dyes featuring D-A′-π-A configuration with 5-methylbenzothiadiazole as auxiliary acceptor have been synthesized and characterized as sensitizer for dye-sensitized solar cell. The dyes with methyl unit attached near donor exhibited high molar extinction coefficients when compared to the isomeric dyes possessing methyl unit near acceptor segment. Due to this, the former dyes exhibited two fold high power conversion efficiencies when compared to the later dyes. The high efficiency of the dyes containing methyl near donor arises from the enhanced photocurrent density and open-circuit voltage values. The electrochemical impedance spectra demonstrated favourable electron injection, longer electron lifetime and effective charge recombination resistance for dye-sensitized solar cells based on these dyes. The attenuation in the coplanarity between the donor and acceptor with benzothiadiazole due to the presence of methyl group significantly affected the donor-acceptor interactions and charge migration kinetics.