Tunable metallic-like transport in polypyrrole

Conjugated polymers (CPs), organic macromolecules with a linear backbone of alternating C-C and C=C bonds, possess unique semiconductive properties, providing new opportunities for organic electronics, photonics, information, and energy devices. Seeking the metallic or metallic-like, even superconducting properties beyond semiconductivity in CPs is always one of the ultimate goals in polymer science and condensed matter. Only two metallic and semi-metallic transport casesaniline-derived polyaniline and thiophene-derived poly(3,4-ethylenedioxythiophene)have been reported since the development of CPs for four decades. Controllable synthesis is a key challenge in discovering more cases. Here we report the metallic-like transport behavior of another CP, polypyrrole (PPy). We observe that the transport behavior of PPy changes from semiconductor to insulator-metal transition, and gradually realizes metallic-like performance when the crystalline degree increases. Using a generalized Einstein relation model, we rationalized the mechanism behind the observation. The metallic-like transport in PPy demonstrates electron strong correlation and phonon-electron interaction in soft condensation matter, and may find practical applications of CPs in electrics and spintronics.