# Prolonged exciton lifetime via conjugation-length engineering in M-series acceptors for 19.39% efficiency polymer solar cells

## TL;DR

Researchers developed new non-fullerene acceptors with improved efficiency and stability for polymer solar cells.

## Contribution

The study introduces dimerized M-series acceptors with extended conjugation and enhanced exciton lifetime.

## Key findings

- DM-8F achieved 19.39% efficiency in small-area solar cells and 15.72% in minimodules.
- DM-8F-based devices showed better thermal and photostability compared to M68-based devices.
- Halogen atoms in terminal groups significantly influenced π–π-packing and photovoltaic performance.

## Abstract

Developing non-fullerene acceptors (NFAs) that combine high device efficiency with superior stability remains a significant challenge. Based on M-series acceptors featuring an acceptor-donor-acceptor (A-D-A)-type framework, we report two dimerized NFAs (DM-8F and DM-8Cl) containing different halogen atoms in their terminal groups. Compared to the small-molecule acceptor M68, both dimerized acceptors exhibit increased glass transition temperatures and enlarged dielectric constants. The choice of halogen atoms in the terminal groups significantly affects their π–π-packing distances, exciton diffusion lengths, and ultimately, photovoltaic performance. Owing to enhanced charge transport, reduced exciton binding energy, and extended exciton diffusion length, DM-8F achieves an efficiency of 19.39% (certified at 19.20%) in small-area polymer solar cells (PSCs) and 15.72% in minimodules with an effective area of 11.09 cm2. These efficiencies are the highest reported to date among all A-D-A-type NFAs. Moreover, DM-8F–based devices exhibit significantly improved thermal and photostability compared to those based on M68.

This work presents an A-D-A-type nonfullerene acceptor featuring an extended conjugation length and enhanced exciton lifetime, which enables stable polymer solar cells with a certified efficiency of 19.20%.