EUROPEAN CONGRESS AND EXHIBITION ON ADVANCED MATERIALS AND PROCESSES - EUROMAT 2021

The water-processable nanoparticles (WPNP) assembled by hydrophobic conjugate polymers represent a new technology that finds application wide range of scientific filed, we focused on the organic photovoltaics (OPVs). In order to obtain a water-stable suspension of WPNPs, we selected four amphiphilic low band gap (LBG) rod-coil block copolymers (BCPs) composed of a rigid hydrophobic p-type semiconductor polymer, PCPDTBT, and 4-vinylpyridine-based (4VP-based) coil block that differ the molecular structure and length of the coil. We supposed that the coil block in the BPC backbone acts as a surfactant during the surfactant-free miniemulsion synthesis of the WPNPs, making the WPNPs stable in water. In order to reduce the use of halogenated solvents in the fabrication of the OPV active layer, we mixed the LBG-BCPs with an electron acceptor fullerene derivative ([6,6]-phenyl-C61-butyricacid methyl ester, PCBM) to achieve blend WPNPs (b-WPNPs). The WPNPs and b-WPNPs were fully characterized by TEM, STEM-EDX, EFTEM, AFM, and DLS and-potential [1,2].
We showed that the WPNP and b-WPNP were spherical but the b-WPNP mean diameter increases as the size distribution. Exploiting the sulfur present in the BCP composition, the STEM-EDX analysis showed the WPNP internal composition. In particular, the rod block, rich in sulfur, thickens mainly in the core of the WPNPs, while the 4VP-based coil tends to locate on the edge, actually acting as a stabilizer. The EFTEM images of the b-WPNPs identified the PCBM rich areas and their shape, allowing to correlate the PCBM distribution inside the WPNP with the material efficiency [3]. In conclusion, we developed a new method to prepare BCP-based WPNPs in aqueous suspensions preventing the use of surfactants, which require long purification procedures. Moreover, we fully characterized the WPNPs and b-WPNPs correlating their characteristics to their properties.

Acknowledgments: MAECI, Direzione Generale per la Promozione del Sistema Paese Italia – Messico (Prot. MAE0044292)