Streamlined synthesis, optoelectronic and photovoltaic characterization of large, monodisperse n-type oligomers via highly efficient direct arylation

• Applicant: Professor Dr. Michael Sommer
• Subject Area: Preparatory and Physical Chemistry of Polymers ; Polymer Materials
• Term: since 2015
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 274393560

The term non-fullerene acceptors (NFAs) is used for n-type organic materials that find increasing use for organic photovoltaics (OPVs). NFAs include both monodisperse, small molecules and disperse conjugated polymers. NFAs have enabled highly efficient photovoltaic devices with strongly improved power conversion efficiencies of 10-15 %. Yet, it is unclear how the major structural differences between these two material classes, dispersity and chain length, contribute to this major improvement. Monodisperse n-type oligomers bridge the gap between these two types of electron acceptor materials. As the exploration of discrete n-type oligomers of varying length has thus far been limited by synthetic access and tedious synthesis pathways, their utility for OPV devices remains unexplored as well. In this proposal, we will synthesize and characterize discrete, monodisperse n-type oligomers of varying chain length. Using mechanistic insight into the direct arylation polycondensation of 2,6-dibromonaphthalene diimide (NDI) and 2,2´-bithiophene (T2) obtained within the last funding period, we will prepare several oligomers (NDIT2)n up to the tritriacontamer (n= 33) with a minimal number of synthetic steps. To make oligomers on gram scale, we aim at chromatography-free purification protocols. These oligomers are unique materials for fundamental optical, thermal and structural investigations. Finally, they will be compared against their disperse, polymeric analog PNDIT2 in order to reveal the effect of dispersity and chain length on properties of both pristine materials as well as of binary all-polymer blends.

• DFG Programme: Research Grants