Synthesis and photovoltaic properties of a series of bulk heterojunction solar cells based on interchain-linked conjugated polymers

Abstract

We have used Suzuki coupling to synthesize a series of maleimide–thiophene copolymers presenting pendent 2-hydroxyethyl and 6-hydroxyhexyl units. The maleimide–thiophene copolymers containing different contents of OH groups were then reacted with 3,3′-dimethoxy-4,4′-biphenylene diisocyanate (DMBPI) in solution to form the interchain-linked polymers. The interchain-linked polymers exhibited excellent solubility in organic solvents. The average molecular weight and thermal stability of the copolymers increased after interchain linking with DMBPI. The wavelengths of maximum absorption of the interchain-linked copolymers were red-shifted relative to those of the corresponding side-chain copolymers. The energy level of the lowest unoccupied molecular orbitals and highest occupied molecular orbitals decreased after the copolymers had undergone interchain linking with DMBPI. We fabricated polymer solar cells (PSCs) from blends of the interchain-linked copolymers and [6,6]-phenyl-C61-butyric acid methyl ester. The photovoltaic performances of the PSCs incorporating the interchain-linked copolymers were superior to those of the corresponding PSCs based on the OH-presenting copolymers.