Water-based nanoparticles dispersions of amphiphilic low band gap block copolymers: an alternative eco-friendly approach

Water-based nanoparticles (NPs) of semiconducting polymers received considerable attention for optoelectronic and biological applications due to their simple preparation method, and their tunable optical properties.1 NPs are appealing for optoelectronic devices such as organic photovoltaic devices (OPVs),2 organic light-emitting diodes (OLEDs),3 and organic field-effect transistors (OFETs)4 to control the morphology of the active layer that plays a crucial role in the device performance. The NPs dispersion can be obtained through the miniemulsion method, using great amount of surfactants to ensure NPs stability. This approach allows for lowering the chlorinated solvent amount used in the active layer fabrication reducing the environmental payback of the devices, but to achieve good performances the excess of surfactant has to be removed at the end of the process.5 Amphiphilic block copolymers (BCPs) are a powerful tool to produce nanostructured or supramolecular objects with enhanced properties for electronics, optoelectronics, sensors and biotechnological applications because of their capability to self-assembly, influenced by the physico-chemical differences between the blocks, including the relative block length, block polarity, volume fraction, chain flexibility, etc.6 PCPDTBT-b-P4VP is an amphiphilic rod-coil BCP constituted by a low band-gap copolymer, PCPDTBT as the rigid segment, and tailored segments of poly-4-vinylpyridine (P4VP). The rod block was studied as donor material in hybrid and organic devices, whilst P4VP is able to interact with acceptor materials, as fullerene derivatives.7 Taking advantage of hydrophilic behavior of the coil, we studied the capability of PCPDTBT-b-P4VP to form NPs dispersion in aqueous medium through miniemulsion method, neat or in blend with fullerene derivatives, without use of surfactants avoiding purification steps. The NPs were optically, morphologically (AFM, TEM, Synchrotron XRD) and electrically characterized, showing suitable properties for the preparation of active layers and they were tested in eco-friendly NP-based OPVs with efficiency reaching over 2%.