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 (J_sc=11.5 mA·cm⁻², PCE 2.5%), with a sustainable fabrication process [9].

It is important to underline that the phase separation between the electron acceptor and donor materials leads to complex internal structures in the nanostructures. This is controlled by the inherent material properties, as long as the solvent evaporates. As in standard OPV devices, the surface energy plays a crucial role in the improvement of the miscibility of two components of the blend. Moreover, the surface energy affects the quality of the active layer’s morphology, enhancing the interfacial area between the materials with an efficient charge generation and dissociation, until the efficiency of the device is increased [10]. We prepared semiconducting blend WPNPs by combining the BCPs with suitable fullerene derivatives, showing higher surface energy with respect to the semiconducting polymers. The high surface energy leads to core–shell blend WPNPs with fullerene derivatives in the core and the electron donor polymers in the shell [11].

In order to clarify how the morphology of the nanodomains into the blend WPNPs is related to the features of the different coil molecular structures in the BCPs, and in turn how they led to different device performances, we achieved a complete spectroscopical, electrical and morphological WPNP characterization [12-14].