Novel 4,4′-bis(alkylphenyl/alkyloxyphenyl)-2,2′-bithiophene bridged cyclic thiourea functionalized triphenylamine sensitizers for efficient dye-sensitized solar cells

Abstract Two novel 4,4′-bis(alkylphenyl/alkyloxyphenyl)-2,2′-bithiophene bridged cyclic thiourea functionalized triphenylamine sensitizers ( D8 and D9 ), comprising 2-cyanoacrylic acid as the acceptor, have been designed and synthesized for dye-sensitized solar cells (DSSCs). For comparison, an analogue ( D7 ) with 4,4′-dihexyl-2,2′-bithiophene spacer was synthesized as well. Their photophysical, electrochemical and photovoltaic properties have been systematically investigated. Compared with D7 , D8 and D9 exhibit red-shifted and expanded absorption bands because aromatic alkylphenyl/alkyloxyphenyl was incorporated into the π-conjugated system, which resulted in an increased short-circuit photocurrent density ( J sc ). In addition, the relatively bulky alkylphenyl/alkyloxyphenyl suppresses intermolecular π–π aggregation and undesired charge recombination more effectively than alkyl chains, thus enhanced open-circuit voltages ( V oc ) were obtained for D8 and D9 . Due to the higher J sc together with the enhanced V oc , D8 and D9 sensitized DSSC devices demonstrate improved power conversion efficiencies (PCEs) up to 7.88% under AM 1.5G irradiation, which surpassed that of D7 (7.41%).