Synthesis and photovoltaic property of new kind of organic dyes containing 2,2′-bithiophene unit with three electron-donors

Abstract

Three new D–π–A conjugated organic sensitizers based on 3,4′,5′-trisubstituted 2,2′-bithiophene were conveniently synthesized. And the photovoltaic performances as well as the structure–property relationship were studied. • Three D–π–A organic dyes containing a π-linker of 2,2′-bithiophene unit linked with three electron-donors have been designed. • The photovoltaic performances of the dyes are characterized and they exhibit relatively high open voltage. • The structure–performance relationship is primarily studied with the aid of theoretical calculation. A series of new organic dyes containing 2,2′-bithiophene unit as a π-linker to connect three electron-donors (including carbazole, DH-45 ; phenothiazine, DH-46 ; triphenylamine, DH-47 ) at 3,4′,5′-positions have been designed and synthesized for dye-sensitized solar cells. The experimental results and theoretic calculations indicated that the large steric hindrance among three electron-donors and 2,2′-bithiophene ring partially destroys the whole molecular coplanarity and weakens intramolecular charge transfer (ICT), which results in the narrow, blue-shift of absorption band and decrease of short-circuit current ( J sc ). However, the twisted conjugation skeleton for the dyes is favorable for the spatial charge separation that enhances the open-circuit voltage ( V oc ). Among them, the dye containing carbazole donating group ( DH-45 ) shows best optimized structure for intramolecular charge transfer (ICT) and exhibits better photovoltaic performances than that of the other two dyes ( DH-46 and DH-47 ).