Green-Solvent-Processed Conjugated Polymers for Organic Solar Cells: The Impact of Oligoethylene Glycol Side Chains

Organic photovoltaics (OPVs) possess the advantageous trait of solution processability, yet OPV blends typically use hazardous chlorinated solvents for processing. In order to realize the full advantages of OPVs, as well as growing to an industrial scale, the use of environmentally friendly solvents for processing OPVs needs to be pursued. In this study, we utilized the well-studied polymer PBnDT-FTAZ system as the model conjugated polymer, and synthesized a series of structurally similar conjugated polymers with oligo(ethylene glycol) (OEG) side-chains, aiming to understand the structural requirements to convert conventional conjugated polymers into green-processable alternatives. We elucidated the impact of these OEG chains on the properties of modified polymers when compared with the original PBnDT-FTAZ, including solubility and optoelectronic properties. Finally, aiming to understand the impact of changing side chains to the device performance, we fabricated solar cells with a nonfullerene acceptor (IT-M), achieving decent device efficiencies (over 7%). Additionally, using renewable and green solvent, 2-methyltetrahydrofuran (2-MeTHF), we were able to achieve device efficiencies of over 2%.