All-polymer solar cells with 19% efficiency via introducing pincer-shaped non-covalent bond interactions

Polymer blends are generally tainted with disordered molecular entanglement, which limits the performance of all-polymer solar cells (all-PSCs). Herein, two small molecules (C5Ph, C6Ph) with phenylalkyl sidechains were developed as an additive to tune all-polymer blends. Assisted by characteristic sidechains, the small molecules afforded multiple non-covalent interactions with a polymer acceptor, which could effectively improve the strength of intermolecular interaction and ordering of PY-IT subcrystalline phases. As a result, the photovoltaic performance and mechanical stability of the all-PSCs were greatly enhanced. Notably, with the addition of independently induced molecular stacking and good vertical phase separation, the pseudo-planar-heterojunction all-PSC achieved a champion efficiency of 19.01% with a nearly 80% fill factor, which is one of the highest values for all-PSCs. Besides, it was demonstrated that the elastic deformation of the active layers can more precisely reflect the mechanical performance of flexible solar cells than conventional elongation at break and elastic modulus. Our work provides intelligent pathways to construct high-performance all-PSCs and reasonably evaluate their mechanical flexibility.