SURFACTANT-FREE MINIEMULSION FOR LOW BAND GAP ROD-COIL BLOCK COPOLYMER WATER-PROCESSABLE NANOPARTICLES: A NEW SUSTAINABLE APPROACH FOR ORGANIC SOLAR CELLS

Water-processable organic nanoparticles (WPNPs) of semiconducting polymers are receiving 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 in optoelectronic devices, such as organic photovoltaics (OPVs), organic light-emitting diodes, and organic field-effect transistors.1 Here we will present a series of four amphiphilic low band gap (LBG) rod-coil block copolymers (BCPs), constituted by a LBG polymer, PCPDTBT, as electrondonor material, and differing for the poly-4-vinylpyridine (P4VP)-based flexible blocks with different length and chemical composition.2,3 We exploited a surfactant-free miniemulsion approach to prepare suspensions stabilized in aqueous medium by the coil block in the BCPs. In order to elucidate the coil block role on the WPNP morphology and stability, we performed a complete WPNP characterization with DLS, TEM, STEM-EDX, and AFM. This study revealed that the rod blocks assemble mainly into the WPNP inner part while the 4VP-based coil segments segregate at the WPNP edge, producing core-shell like nanostructures.4 Moreover, we prepared semiconducting blend WPNPs by combining the LBG rod-coil BCPs with [6,6]-phenyl-C61-butyric acid methyl ester (PC61BM), which can act as electron acceptor in OPVs. We achieved adequate morphologies in the blend WPNP aqueous suspensions, without non-conducting surfactant use. Pump-probe measurements were used to gain information on ultrafast phenomena, such as donor-acceptor charge generation rate into the blend WPNP casted films. 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, considerably reducing halogenated solvent use.5