Understanding How to Control Efficiency of Benzimidazoline Based n-type Dopants: A Structural Approach

Molecular doping is pivotal to improve charge transport properties of organic semiconductors. With respect to the p-type counterpart, n-type doping is more challenging, due to the air sensitivity of the required electron rich dopants. The use of kinetically stabilized dopants precursors showed to be an efficient strategy to circumvent this issue. Among these, the benzimidazoline derivative N-DMBI-H is one of the most widely used, but its scarce miscibility within the semiconductors matrix limits its doping efficiency. The research for new benzimidazoline based dopants with improved performances has thus emerged. In this work, we study the doping of the n-type polymer P(NDI2OD-T2) with a set of new N-DMBI-H-like dopants bearing different molecular functionalization patterns. By combining optical and electrical characterization, we analyse the influence of the introduced structural modifications on the compounds performances. Via morphological characterization, we then reveal a relation between the efficiency of the analysed dopants and their solid-state interactions with the semiconductor host, highlighting that the most performing dopants are those characterized by improved intercalation in the semicrystalline polymeric microstructure and lower tendency to segregation. Our results are supported by computational studies and can help in the definition of design guidelines for more performing benzimidazoline based n-type dopants.