π-Extended low bandgap polymer based on isoindigo and thienylvinylene for high performance polymer solar cells

Abstract

A π-extended low bandgap polymer (PiITVT) consisting of isoindigo and thienylvinylene is synthesized and used as an active layer material for polymer solar cells. PiITVT-based polymer solar cells exhibited a high power conversion efficiency of 7.09%, which is higher than that of PiI2T (5.55%), because of the better coplanar structure of the TVT unit than the 2T unit.

Low bandgap conjugated polymers based on a donor–acceptor (D–A) structure are an emerging class of donor materials for high performance polymer solar cells (PSCs). Molecular design and synthesis of conjugated polymers and deep understanding of the relation between chemical structure and photophysical properties are crucial to develop high performance PSCs. One of the effective approaches to develop efficient conjugated polymers is to strengthen the intermolecular interaction between conjugated polymer chains by enhancing their molecular orbital overlap. For this purpose, we synthesized a p-extended low bandgap polymer composed of thienylvinylene and isoindigo, which exhibits high crystallinity, low-lying highest occupied molecular orbital level and favorable molecular orientation in a blend film with PCBM. The PSC device shows a promising power conversion efficiency of 7.1%. Hence, thienylvinylene is a promising building block for constructing high performance conjugated polymers.