Rod-coil block copolymer:fullerene water-processable nanoparticles: how molecular design addresses morphology and efficiency in NP-OPVs

The fabrication of the active layers in optoelectronic devices involves the use of large amounts of chlorinated organic solvents on the laboratory scale (i.e., chloroform, chlorobenzene, dichlorobenzene) in order to obtain morphology with an optimized interpenetrating network between electron donor and acceptor materials [1]. The ideal industrial production should be highly sustainable dramatically reducing the use of chlorinated solvents, then the environmental impact and the manufacturing cost of the devices [2,3]. Water-processable organic nanoparticles (WPNPs) of semiconducting polymers recently received wide attention for optoelectronic applications due to their simple fabrication and tunable properties. The WPNP-based approach could be appealing to control active layer morphology, and considerably reducing halogenated solvent use.[4] Here we will report about a series of amphiphilic low band gap rod-coil block copolymers (BCPs), constituted by semiconducting electron donor polymers as the rigid segment (PCPDTBT and PTB7), and differing for the poly-4-vinylpyridine (P4VP)-based flexible blocks with different length and chemical composition.[5-8] These materials were designed in order to prepare blend WPNPs in aqueous suspensions with surfactant-free miniemulsion approach exploiting the interaction of the P4VP-based flexible segments with the non-solvent aqueous phase. Thus, we were able to prepare working OPV devices, exhibiting high short-circuit current density (Jsc=11.5 mA·cm−2, PCE 2.5%), with a sustainable fabrication process [9].