# Fluorinated Benzodipyrrole-Based Non-Fullerene Acceptors with Chlorinated End Groups Exhibiting Fluorine–Chlorine Interactions for Suppressed Charge Recombination in Organic Photovoltaics

## TL;DR

This paper introduces new fluorinated and chlorinated organic materials that improve solar cell efficiency by enhancing charge transport and reducing recombination.

## Contribution

The study introduces fluorine–chlorine interactions in non-fullerene acceptors to enhance charge transport and device performance in organic photovoltaics.

## Key findings

- CFB-Cl achieved a PCE of 16.62% with a fill factor of 75.54%.
- Ternary blends with CMB improved PCE to 17.26% with balanced carrier transport.
- F···Cl interactions led to compact molecular packing and efficient charge transport.

## Abstract

Two terminal-chlorinated ortho-benzodipyrrole
(o-BDP)-based non-fullerene acceptors (NFAs), CFB-Cl
and CMB-Cl, were designed and synthesized by incorporating fluorine
or methyl substituents on the o-BDP core, respectively.
Compared to their terminal-fluorinated counterparts, both NFAs exhibit
red-shifted absorption, higher melting points, and stronger intermolecular
interactions, attributed to the introduction of chlorinated end groups.
Single-crystal X-ray analysis of CFB-Cl revealed a compact three-dimensional
kaleidoscopic packing network stabilized by unique F···Cl
halogen interactions between the fluorinated o-BDP
core and the chlorinated end group, leading to a short π–π
stacking distance of 3.38 Å and enhanced charge transport. Consequently,
PM6:CFB-Cl devices achieved a PCE of 16.62% with a fill factor (FF)
of 75.54%, outperforming PM6:CMB-Cl (PCE = 16.13%). To further improve
device performance, a ternary blend strategy was employed by introducing
the fluorinated CMB into PM6:CFB-Cl blends to extend the absorption
range and improve the morphology. The resulting PM6:CFB-Cl:CMB inverted
device exhibited excellent miscibility (χ = 0.02 K), balanced
carrier transport (μe/μh = 1.38),
suppressed recombination, and a highest PCE of 17.26% with J
sc = 26.02 mA cm–2 and V
oc = 0.892 V. This work highlights the importance
of halogen engineering in regulating molecular packing and charge
dynamics, providing insights into the structure–morphology–performance
relationship of o-BDP-based NFAs for next-generation organic photovoltaics.