Engineering the self-assembly of diketopyrrolopyrrole-based molecular semiconductors via an aliphatic linker strategy

Abstract

The solid-state self-assembly of molecular semiconductors is a key aspect for controlling the optoelectronic properties of organic electronic materials. Herein, we investigate the use of a flexible linker strategy to control the self-assembly of a solution-processable diketopyrrolopyrrole semiconductor coded as DPP(TBFu)2. Two distinct dimers - prepared with varied linker position relative to the orientation of the conjugated core - reveal the effect of connectivity on the solid-state self-assembly and optoelectronic properties - favoring either H- or J-type aggregation. The dimer with a "vertical" linker orientation exhibits a poor crystallinity in neat films, but improves hole mobility in OFETs 10-fold, reaching 3.0 × 10-3 cm2 V-1 s-1 when used as an additive with DPP(TBFu)2. Distinctively, the dimer with a "horizontal" linking orientation does not enhance charge carrier transport, but is found to affect the thermal stability of donor : acceptor blends in OPVs with PCBM. Devices retain 90% of their initial conversion efficiency after 5 hours of thermal stress, compared to only 45% for control devices. Thermodynamic and kinetic rationales further suggest that this flexible linker strategy represents a powerful tool to control supramolecular assembly in molecular semiconductors without altering the nature of the core conjugated segment.