In recent years the development of new NFA molecules has been increasing performances and competitiveness. The new generations of NFAs offers tremendous advantages, like extended absorption ranges, better complementarity with polymers absorption, optimized blend morphologies and miscibility, along with better charge transport and exciton splitting properties. Despite showing efficiencies above 18% (1) the industrial transfer of OPV devices and their penetration to the market remains low, principally due to the need of improving industrial processes and long-term stability. On these days some of the new families of molecules seems to be very promising for industrial transfer. New generation of NFAs focus more on enhance efficiency, the Y6 molecule for example, shows an impressive efficiency of 15% (3), but this molecule is only soluble in halogenated solvents. Subsequent studies succeeded in solubilizing the molecule in non-halogenated solvents with 16% efficiency and similar results for blade coating fabrication.(4) However, stability tests and industrial transfer are still missing for this type of molecules. On this regard, it appears crucial to develop materials compatible with industrial requirements and intrinsically stables in parallel with their performances.

Today, a large library of building blocks is available to prepare NFAs with tunable optical and electronic properties. For the optimization of the performances in solar cells, it is necessary to focus on the development of narrow band gaps NFAs with a broad and intense absorption in the visible range and suitable LUMO energy level to maximize the open-circuit voltage (V_oc), but additionally, they should demonstrate high stability and non-halogenated solvents compatibility for industrial use. Keeping in mind this requirement, we propose a molecular design inspired by ITIC molecules with an extended electron-donating core and functionalized with solubilizing groups. We synthesized and characterized a series of four NFAs called BITIC-C8, BITIC-PhC6, BITIC-PhC6F4 and BITIC-C8F4 based on an 4,9-dihydro-s-indaceno[1,2-b:5,6-b']dithiophene (IDT) central core.(5) The influence of the nature of the solubilizing groups and the presence of fluorine atoms on properties and performance of the molecules, was investigated. Interestingly, we observe increased photo-stability of the molecules in thin films, compare to reference ITIC. The photovoltaic performances of the four NFAs were assessed in binary blends using PM6 as the donating polymer and in ternary blends with ITIC-4F. Solar cells show power conversion efficiencies of up to 11.1% in ternary blends processed from non-halogenated solvents and without any thermal post-treatment, making this process more compatible with industrial requirements.(5)