Hole-transporting alternating copolymers for perovskite solar cells: thia[5]helicene comonomer outperforms planar perylothiophene analog

Abstract

Semiconducting polymers with high glass transition temperatures play a pivotal role in advancing thermally tolerant organic optoelectronic devices. This investigation underscores the remarkable potential of helicene as a comonomer in the construction of semiconducting polymers. Non-planar thia[5]helicene or planar perylo[1,12-bcd]thiophene is co-polymerized in an alternating fashion with 3,4-ethylenedioxythiophene, phenoxazine, and 3,4-ethylenedioxythiophene, resulting in two quaternary alternating copolymers. The thiahelicene-based alternating copolymer, characterized by a deeper HOMO energy level, exhibits decelerated hole extraction kinetics and diminished hole density compared to its perylothiophene-based counterpart. Notably, due to enhanced solubility, the thiahelicene-based copolymer demonstrates increased molecular weight, which contributes to higher glass transition temperature and hole mobility. When utilized as a hole transport material in n–i–p type perovskite solar cells, the thiahelicene-based copolymer demonstrates an elevated average power conversion efficiency (25.2%), enhanced thermal storage stability, and improved operational endurance.