Organic dyes incorporating a thiophene or furan moiety for efficient dye-sensitized solar cells

Abstract

Four novel carbazole organic dyes containing either a furan or a thiophene unit as the conjugated bridge have been designed, synthesized and characterized for nanocrystalline TiO2 dye-sensitized solar cells. The modified carbazole containing linear or branched alkyl side chain acts as an electron donor, triphenylamine acts as an electron-donating group and cyanoarylic acid acts as an electron acceptor and anchoring unit. The absorption spectra, electrochemical, photovoltaic and sensitizing properties of the new dyes were fully characterized. Among these four dyes, the dye incorporating an octyl-substituted carbazole and disubstituted furan shows the best photovoltaic performance: a maximum monochromatic incident photon-to-current conversion efficiency of 92.4%, a short-circuit photocurrent density of 13.26 mA cm−2, an open-circuit photovoltage of 724 mV, and a fill factor of 0.66, corresponding to an overall conversion efficiency of 6.68% under standard global AM 1.5 solar light condition. The results indicate that the introduction of longer alkyl chain into the carbazole moiety will retard recombination and the introduction of furan as the conjugate bridge will increase the photocurrent response. For comparison, the ruthenium dye, designated as N719, sensitized TiO2 solar cell showed an efficiency of 6.98% under the same experiment conditions.