A solution-processed n-type conducting polymer with ultrahigh conductivity.

Conducting polymers (CPs) with high conductivity and solution processability have made great advances since the pioneering work on doped polyacetylene^1-3, thus creating the new field of 'organic synthetic metals,⁴. Various high-performance CPs have been realized, which enable the applications of several organic electronic devices^5,6. Nevertheless, most CPs exhibit hole-dominant (p-type) transport behaviour^7,8, whereas the development of n-type analogues lags far behind and only a few exhibit metallic state, typically limited by low doping efficiency and ambient instability. Here we present a facilely synthesized highly conductive n-type polymer poly(benzodifurandione) (PBFDO). The reaction combines oxidative polymerization and in situ reductive n-doping, greatly increasing the doping efficiency, and a doping level of almost 0.9 charges per repeating unit can be achieved. The resultant polymer exhibits a breakthrough conductivity of more than 2,000 S cm^-1 with excellent stability and an unexpected solution processability without extra side chains or surfactants. Furthermore, detailed investigations on PBFDO show coherent charge-transport properties and existence of metallic state. The benchmark performances in electrochemical transistors and thermoelectric generators are further demonstrated, thus paving the way for application of the n-type CPs in organic electronics.