Environmentally friendly preparation of nanoparticles for organic photovoltaics

Aqueous nanoparticle dispersions were prepared from a conjugated polymer poly[thiophene-2,5-diyl-alt-5,10-bis((2-hexyldecyl)oxy)dithieno[3,2-c:3',2'-h][1,5]naphthyridine-2,7-diyl] (PTNT) and fullerene blend utilizing chloroform as well as a non-chlorinated and environmentally benign solvent, o-xylene, as the miniemulsion dispersed phase solvent. The nanoparticles (NPs) in the solid-state film were found to coalesce and offered a smooth surface topography upon thermal annealing. Organic photovoltaics (OPVs) with photoactive layer processed from the nanoparticle dispersions prepared using chloroform as the miniemulsion dispersed phase solvent were found to have a power conversion efficiency (PCE) of 1.04%, which increased to 1.65% for devices utilizing NPs prepared from o-xylene. Physical, thermal and optical properties of NPs prepared using both chloroform and o-xylene were systematically studied using dynamic mechanical thermal analysis (DMTA) and photoluminescence (PL) spectroscopy and correlated to their photovoltaic properties. The PL results indicate different morphology of NPs in the solid state were achieved by varying miniemulsion dispersed phase solvent.