Star-shaped benzotriindole-based donor compounds for all–small–molecule non-fullerene organic solar cells

The recent success in the development of non-fullerene acceptors (NFAs) for organic solar cells (OSCs) encourages the search for novel efficient and complementary donor materials. Moreover, the in-depth understanding of the structure–property correlations for new generations of acceptor and donor materials is of great importance for the further progress in the field of OSCs. In this work the synthesis of a series of star-shaped small molecules based on benzotriindole (BTI) electron-donating core linked through bi– or terthiophene π-spacers to either hexyl dicyanovinyl or 2-ethylhexyl cyanoacetate electron-withdrawing terminal groups (EWGs) is reported. The thermal, optical and electrochemical properties of the molecules were carefully investigated and compared. The molecules were also explored as donor materials in non-fullerene (NF) OSCs in binary blends with well-known NFAs such as IDIC or Y6. The huge impact of the donor molecular structure on the device performance (up to 6 times difference in power conversion efficiency (PCE)) was evaluated due to significant difference in the active layer morphologies, which was successfully proved via scanning near-field infrared microscopy technique. The results obtained in this work demonstrate high potential of star-shaped BTI-based molecules to be used as donor materials with a new generation of NFAs and can be used for further molecular design of the highly efficient small molecule donors for NF OSCs.