Study on water/ethanol-soluble naphthalene diimide (NDI)-based conjugated polymers for eco-friendly all-polymer solar cells

Abstract

The use of toxic halogenated solvents, commonly used in the manufacture of polymer solar cells (PSCs), are highly detrimental to humans and the environment, and is a major constraint on commercial use. In this context, we synthesized a series of water/ethanol-soluble naphthalene diimide (NDI)-based polymers and utilized them in the photoactive and electron transporting layers (ETLs) in PSCs. To ensure sufficient solubility in the eco-friendly solvents, hydrophilic olygoethylene glycol (OEG) side chains were introduced, and consequently three novel polymers (P(NDIDEG-T), P(NDITEG-T), and P(NDITEG-T2)) having different lengths of the side chain or the backbone structures were synthesized. When P(NDIDEG-T), which has the shortest OEG side chain, was used as the electron acceptor in the photoactive layer, a remarkable power conversion efficiency (PCE) of 2.15% was achieved. Interestingly, the PSC devices maintained more than 90% of the initial performance in the ambient condition even after 4 days