Marina, SaraScaccabarozzi, Alberto D.Gutiérrez Fernández, EdgarSolano, EduardoKhirbat, AditiCiammaruchi, LauraIturrospe, AmaiaBalzer, AlexYu, LiyangGabirondo, ElenaMonnier, XavierSardón, HaritzAnthopoulos, Thomas D.Caironi, MarioCampoy-Quiles, MarianoMüller, ChristianCangialosi, DanieleStingelin, NatalieMartín, Jaime2021-08-232021-08-232021Marina, S., Scaccabarozzi, A. D., Gutierrez-Fernandez, E., Solano, E., Khirbat, A., Ciammaruchi, L., Iturrospe, A., Balzer, A., Yu, L., Gabirondo, E., Monnier, X., Sardon, H., Anthopoulos, T. D., Caironi, M., Campoy-Quiles, M., Müller, C., Cangialosi, D., Stingelin, N., Martin, J., Polymorphism in Non-Fullerene Acceptors Based on Indacenodithienothiophene. Adv. Funct. Mater. 2021, 31, 2103784. https://doi.org/10.1002/adfm.202103784http://hdl.handle.net/2183/28274Financiado para publicación en acceso aberto: Universidade da Coruña/CISUG[Abstract] Organic solar cells incorporating non-fullerene acceptors (NFAs) have reached remarkable power conversion efficiencies of over 18%. Unlike fullerene derivatives, NFAs tend to crystallize from solutions, resulting in bulk heterojunctions that include a crystalline acceptor phase. This must be considered in any morphology-function models. Here, it is confirmed that high-performing solution-processed indacenodithienothiophene-based NFAs, i.e., ITIC and its derivatives ITIC-M, ITIC-2F, and ITIC-Th, exhibit at least two crystalline forms. In addition to highly ordered polymorphs that form at high temperatures, NFAs arrange into a low-temperature metastable phase that is readily promoted via solution processing and leads to the highest device efficiencies. Intriguingly, the low-temperature forms seem to feature a continuous network that favors charge transport despite of a poorly order along the π–π stacking direction. As the optical absorption of the structurally more disordered low-temperature phase can surpass that of the more ordered polymorphs while displaying comparable—or even higher—charge transport properties, it is argued that such a packing structure is an important feature for reaching highest device efficiencies, thus, providing guidelines for future materials design and crystal engineering activities.engAtribución-NoComercial-SinDerivadas 4.0 Internacionalhttp://creativecommons.org/licenses/by-nc-nd/4.0/Non-fullerene acceptorsOrganic electronicsOrganic semiconductorsOrganic solar cellsPolimorphismjournal articleopen access10.1002/adfm.202103784