Conductive ionenes were synthesized by integrating the electron donor dialkoxynaphthalene (DAN) with the electron acceptor naphthalene diimide (NDI) using the Menshutkin reaction. The crystallinity and morphology of the films of these polymers can be optimized by varying the DAN-to-NDI ratio. These ionenes show strong charge transfer from DAN to NDI, though absent conjugated backbones, affording self-doping polymers with enhanced π-π interactions and excellent electronic properties. This is the first example where an electron donor can dope the electron acceptor in nonconjugated polymers, opening a new avenue for designing efficient interlayer materials. These ionenes markedly modify the electrode interface and promote efficient interfacial self-doping to boost the performance of fullerene-based, non-fullerene-based, and ternary organic solar cells, affording high power conversion efficiencies over a wide range of interlayer thicknesses, from ∼8 to ∼40 nm, with a maximum efficiency of 17.05%.
Keywords: interface engineering; interfacial doping; ionene polymers; organic semiconductors; organic solar cells.