Published in Advanced Optical Materials | Volume 13, Issue 10, 2025 | First published: 23 January 2025 | DOI: 10.1002/adom.202402954
Wenle Tana, Hanlin Gana, Yue Yu*a, Feng Heb, Yuguang Ma*a
* Corresponding Authors | Yuguang Ma ORCID: 0000-0003-0373-5873
For photovoltaic materials, large molar extinction coefficients and low band-tailing absorption are critical for efficient photon utilization and reduced energy loss. Non-fullerene acceptors (NFAs) such as ITIC and Y6 have significantly advanced photovoltaic performance, thanks to their strong absorption and steep band edges.
Analysis of ITIC and Y6 reveals that their frontier orbitals are mainly distributed on the central conjugated backbones (with minimal distribution on electron donor and terminal acceptor segments), indicating a localized electronic signature rather than a charge transfer state. Single-crystal structures of ITIC and Y6 show that their π-conjugated backbones exhibit homogeneous carbon-carbon (C-C) bond lengths; meanwhile, calculated atomic charge distributions demonstrate alternating positive and negative partial charges on the carbon atoms of these π-conjugated backbones—collectively revealing soliton-like electronic structural characteristics in these molecules.
Inspired by cyanine dyes (which exhibit similar soliton features and excellent spectral performance), these soliton-like characteristics are identified as the origin of the strong, tailless absorption spectra of ITIC and Y6. Further analysis shows that introducing an acceptor group (benzothiadiazole) induces more extensive soliton waves in the conjugated backbone of Y6 (compared to ITIC), leading to stronger absorption and a steeper band edge. These findings suggest that soliton-type NFA materials offer a new insight for designing high-performance organic photovoltaic materials.
Non-fullerene acceptors (NFAs) with a donor-acceptor-donor (D-A-D) structure (e.g., ITIC, Y6) have become core materials for organic solar cells (OPVs) due to their rigid backbones, near-infrared (NIR) absorption, and high power conversion efficiency (PCE)—current state-of-the-art OPVs based on ITIC and Y-series NFAs have achieved PCEs exceeding 15% and 20%, respectively.
However, the design mechanism of NFAs remains a major challenge for breaking bottlenecks in efficiency, stability, and industrialization. Establishing a clear relationship between molecular structure and material properties is urgent for further development. This study, inspired by cyanine dyes, reveals the soliton-like electronic nature of NFAs, filling the gap in the understanding of NFA spectral performance origins and providing a novel strategy for the rational design of high-performance photovoltaic materials.