Photovoltaic properties of three new cyanine dyes for dye-sensitized solar cells

Abstract

Three carboxylated cyanine dyes, 2-[(1-butyl-3,3-dimethyl-5-carboxylindoline-2-ylidene)propenyl]-[1-butyl-3,3-dimethyl-7-(1-ethyl-1H-1,2,3-triazole-4-yl]-1H-benz[e]indolium iodide (Cy1), 2-[(1-butyl-3,3-dimethyl-5-carboxyl-indoline-2-ylidene)propenyl]-{1-butyl-3,3-dimethyl-7-[(4-piperidine-N-ethyl-1,8-naphthalimide)-1H-1,2,3-triazole-4-yl]}-1H-benz[e]indolium iodide (Cy2) and 2-[(1-butyl-3,3-dimethyl-5-carboxyl-indoline-2-ylidene)propenyl)-[1-butyl-3,3-dimethyl-7-{(4-piperidine-N-butyl-1,8-naphthalimide)-1H-1,2,3-triazole-4-yl}]-1H-benz[e]indolium iodide (Cy3), have been synthesized and characterized with regard to their structures and electrochemical properties. Upon adsorption onto a TiO₂electrode, the absorption spectra of the three cyanine dyes are all broadened to both red and blue sides compared with their respective spectra in an acetonitrile and ethanol mixture. Cy2 and Cy3, containing a naphthalimide group, have stronger absorption intensities and broader absorption spectra than Cy1, which consequently leads to better light-to-electricity conversion properties. Among the three cyanine dyes, Cy3 generated the highest photoelectric conversion yield of 4.80% (J_sc = 14.5 mA cm^–2, V_oc = 500 mV, FF = 0.49) under illumination with 75 mW cm^–2 white light from a Xe lamp.