Non-Fullerene Acceptors with an Extended π-Conjugated Core: Third Components in Ternary Blends for High-Efficiency, Post-Treatment-Free Organic Solar Cells

The synthesis of four non-fullerene acceptors (NFAs) with a A-pi-D-pi-A structure, in which the electron-donating core is extended, was achieved. The molecules differed by the nature of the solubilizing groups on the pi-spacer and/or the presence of fluorine atoms on the peripheral electron-accepting units. The optoelectronic properties of the molecules were characterized in solution, in thin film, and in photovoltaic devices. The nature of the solubilizing groups had a minor influence on the optoelectronic properties but affected the organization in the solid state. On the other hand, the fluorine atoms influenced the optoelectronics properties and increased the photo-stability of the molecules in thin films. Compared to reference ITIC, the extended molecules showed a wider absorption across the visible range and higher lowest unoccupied molecular orbital energy levels. The photovoltaic performances of the four NFAs were assessed in binary blends using PM6 (PBDB-T-2F) as the donating polymer and in ternary blends with ITIC-4F. Solar cells (active area 0.27 cm(2)) showed power conversion efficiencies of up to 11.1 % when ternary blends were processed from non-halogenated solvents, without any thermal post-treatment or use of halogenated additives, making this process compatible with industrial requirements.

Automated summary

Four non-fullerene acceptors (NFAs) with extended electron-donating cores and varying solubilizing groups and fluorine atoms were synthesized. The solubilizing groups had minimal impact on optoelectronic properties but influenced organization in the solid state, while the presence of fluorine atoms enhanced optoelectronics properties and increased photo-stability in thin films. Compared to a reference material, the NFAs showed improved absorption across the visible range and higher energy levels. With PM6 as the donating polymer, the NFAs achieved high power conversion efficiencies in solar cells without the need for thermal post-treatment or halogenated additives, making them suitable for industrial applications.