# Computation-Guided Placement of Nonfullerene Acceptor Core Halogenation for High-Performance Organic Solar Cells

## TL;DR

This paper shows how placing bromine on a key part of a molecule improves the efficiency of organic solar cells.

## Contribution

A new series of brominated nonfullerene acceptors is designed and shown to significantly boost solar cell performance.

## Key findings

- Brominated NFAs achieved a power conversion efficiency of 17.58%, outperforming fluorinated and chlorinated variants.
- Bromination improved film morphology, exciton dissociation, and charge mobility in organic solar cells.
- Ternary solar cells with brominated NFAs reached a record 20.14% efficiency.

## Abstract

The strategic molecular
design of nonfullerene acceptors (NFAs)
plays a crucial role in enhancing the efficiency of organic solar
cells (OSCs). Here, working from first-principles theoretical computation,
we report a new series of quinoxaline-based NFAs (Qx-PhHal, where Hal = F, Cl, or Br) with varying halogen substitution on
the central acceptor core of the molecules to investigate their impact
on OSC performance. Notably, OSCs incorporating the brominated NFA
demonstrate a significantly higher power conversion efficiency (PCE
= 17.58%) than those with fluorinated or chlorinated NFAs (∼14%).
Theoretical and experimental analyses reveal that bromination enhances
electrostatic interactions, donor–acceptor miscibility, crystallinity,
and fibrillar film morphology versus the other halogenated NFAs, thereby
enhancing exciton dissociation efficiency, more balanced hole/electron
mobility, and reduced exciton recombination rates in the corresponding
OSCs. Additionally, ternary solar cells incorporating the brominated
NFA as the third component achieve a very high PCE of 20.14%. These
findings provide valuable insights into the molecular design of future
high-performance NFAs for OSC applications.