Chlorine-free processed high performance organic solar cells

The processing of polymer solar cells with non-halogenated solvents is highly desirable in order to achieve an environmentally friendly, sustainable large-scale fabrication of organic photovoltaics. This work demonstrates device processing free of chlorinated solvents yielding high-performance polymer: fullerene bulk-heterojunction solar cells comprising a conjugated polymer poly{[4,8-bis-(2-ethyl- hexyl-thiophene-5-yl)-benzo[1,2-b: 4,5-b0] dithiophene-2,6-diyl]-alt-[2-(20-ethyl-hexanoyl)-thieno [3,4-b] thiophen-4,6-diyl]} (PBDTTT-CT) and a fullerene derivative [6,6]-phenyl-C-70-butyric acid methyl ester (PC70BM). As compared to chlorobenzene/ ortho-dichlorobenzene cast devices the overall solar cell performance could be improved from 6.71% up to 7.15% by using xylene-based solvent systems.