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

Jeanbourquin, Xavier A., Rahmanudin, Aiman, Gasperini, Andrea, Ripaud, Emilie, Yu, Xiaoyun, Johnson, Melissa, Guijarro, Néstor, Sivula, Kevin
Journal of materials chemistry A 2017 v.5 no.21 pp. 10526-10536
crystal structure, semiconductors, thermal stability, thermal stress
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.