Synergistic effects of copolymerization and fluorination on acceptor polymers for efficient and stable all-polymer solar cells

Abstract

Growing efforts have been devoted to developing polymer acceptors as alternatives to fullerene derivatives to realize durable and high-performance all-polymer solar cells (all-PSCs). In retrospect, the non-ideal morphology is thought to be one of the key constraints, which significantly limits the short-circuit current density (J_sc) of all-PSCs (<15 mA cm⁻²). Motivated by the recent copolymerization and fluorination concepts, we herein synthesize three new acceptor polymers by incorporating a fraction of fluorinated thiophenes onto the naphthalene diimide (NDI)-bithiophene backbones. On the basis of enough energy offsets and optimal blend morphology, the fluorinated acceptor polymers can also increase the dielectric constants, all of which synergistically improve the exciton dissociation in the active layers. As a result, the all-PSCs attain high and stable PCEs of 8.0%. The outstanding J_sc of 15.08 mA cm⁻² is one of the highest values achieved by the all-PSCs, specifically for those based on fluorinated acceptor polymers. The performance of the all-PSCs also exhibits good tolerance in a wide range of active areas and active layer thickness. In addition to the high-performance all-PSCs based on a rigid substrate, flexible all-PSCs are realized with encouraging PCEs approaching 6.0%, which exhibits one of the best performances among the state-of-the-art flexible all-PSCs. This work paves an avenue for developing high-performance acceptor polymers via copolymerization and fluorination concepts and discloses the potential of the all-PSCs for robust and mass production.