Abstract
The synthesis of four non-fullerene acceptors (NFAs) with a "A-π-D-π-A" structure, in which the electron-donating core is extended, was achieved. The molecules differed by the nature of the solubilizing groups on the π-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 cm2 ) 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.
Highlights
Organic solar cells (OPV) have faced a strong increase of their performances and competitiveness in the last few years
We notably demonstrate that the nature of the solubilizing groups borne on the 4H-indeno[1,2-b]thiophene spacers has a minor influence on the optoelectronic properties but affects the organization in thin films and the performances in solar cells
Introducing donating spacers bearing solubilizing groups is a strategy aiming at decreasing energy losses in solar cells by rising the LUMO level while facilitating processability compared to ITIC.[28,29]
Summary
Organic solar cells (OPV) have faced a strong increase of their performances and competitiveness in the last few years. When we employed the fluorinated derivatives BITIC-PhC6F4 and BITIC-C8F4 in ternary blends comprising PM6 and ITIC-4F as a second electron acceptor compatible with non-halogenated solvents, higher performances were obtained with PCEs over 11%.
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