Low-cost dyes based on methylthiophene for high-performance dye-sensitized solar cells

Three donor–acceptor, π-conjugated (D–π–A) dyes containing methylthiophene or vinylene methylthiophene as π-conjugated spacer were utilised in dye-sensitized nanocrystalline TiO2 solar cells. The relationship between the structure of the dyes and their photophysical, electrochemical and photovoltaic properties was investigated systematically. The vinyl unit, introduced as the π-conjugated spacer, leads to unfavorable back-electron transfer and decrease of the open-circuit voltage. A dye-sensitized solar cell based on 2-cyano-3-(5-(4-(diphenylamino)phenyl)-4-methylthiophenyl-2-yl) acrylic acid displayed the most efficient solar-to-electricity conversion efficiency of the dyes with a maximum η value of 8.27% (Voc = 0.72 V, Jsc = 15.76 mA cm−2, FF = 0.73) under simulated AM 1.5 G solar irradiation (100 mW cm−2).