Chlorine-Mediated Dispersion Modulates Packing Arrangement of Asymmetric Acceptors for High-Performance Organic Solar Cells

Abstract

This study focuses on the synthesis and the performance of non-fullerene acceptors (NFAs) with varying chlorine dispersion in organic solar cells (OSCs). Four chlorine-mediated acceptors, BO3Cl-a, BO3Cl-γ, BO3Cl-β, and BOEH3Cl-β are synthesized with isomeric terminal groups and then integrated with donor PBDB-TF to fabricate OSCs. It finds that increased chlorine dispersion improves device efficiency with enhanced current and BOEH3Cl-β-based devices achieving a power conversion efficiency (PCE) of over 19%, which is one of the highest values reported for asymmetrically chlorinated acceptors. In OSC devices, Enhanced exciton dissociation and reduced carrier recombination are observed with more chlorine dispersion, along with improved charge transport due to modulation of molecular packing in the active layer. Furthermore, transient absorption spectroscopy elucidates that chlorine dispersion augments exciton diffusion time, thereby elevating the current density of devices, while the branching strategy further amplify the exciton lifetime of BOEH3Cl-β, preserving the value of short current in the face of spectral blue shifts of it. The findings suggest that chlorine-mediated dispersion is a key factor in enhancing OSC performance with improved current by progressive molecular packing arrangement and aggregation behaviors.