Benzodithiophene based organic dyes for DSSC: Effect of alkyl chain substitution on dye efficiency

Abstract

A series of push–pull triarylamine organic dyes containing the benzo[1,2-b:4,5-b′]dithiophene unit as a spacer and bearing alkyl chains in different positions of the molecule were synthesized. The new dyes 1–4 were characterized by optical and electrochemical measurements and density functional theory calculations and used as sensitizers in liquid dye-sensitized solar cells. The effect of alkyl chain position on dye properties and performances was investigated and dye 1, bearing two 3,7-dimethyloctyl groups on the benzodithiophene core, exhibited the best behaviour in term of light absorption and cell performance (PCE of 6.6%, to be compared with a PCE of 8.1% for N719-based device). The efficiency of the DSSC was highly dependent on the solvent used for the dye-sensitizing bath, which affects the position of the COOH/COO− equilibrium.