π-conjugated naphthodithiophene homopolymers bearing alkyl/alkylthio-thienyl substituents: facile synthesis using hexamethylditin and their charge-transport and photovoltaic properties

Abstract

Two π-conjugated naphtho[1,2-b:5,6-b']dithiophene (NDT)-based homopolymers functionalized with alkyl-thienyl or alkylthio-thienyl side chains were designed and synthesized via palladium-catalyzed dehalogenative polycondensation using hexamethylditin as the condensation reagent. Their photophysical properties and device performances for organic field-effect transistors and organic solar cells were systematically studied. Replacing lateral alkyl-thienyl substituents with alkylthio-thienyl ones led to better photoabsorption properties and a deeper-lying HOMO energy level of the resulting NDT homopolymers. The alkylthio-thienyl-functionalized NDT homopolymer showed a higher hole mobility and superior photovoltaic properties compared with the alkyl-thienyl homolog. Two new π-conjugated naphtho[1,2-b:5,6-b']dithiophene (NDT)-based homopolymers functionalized with alkyl-thienyl or alkylthio-thienyl side chains were synthesized and characterized. To simplify the synthetic route, we performed the palladium-catalyzed dehalogenative polycondensation using hexamethylditin as the condensation reagent. The alkylthio-thienyl-functionalized NDT-based homopolymer exhibited a higher hole mobility in organic field-effect transistors (OFETs) and higher power conversion efficiency in organic solar cells (OSCs), compared to alkyl-thienyl-functionalized one.