A compound containing at least two pyridinium derivatives in its molecular structure and being in a reduced form thereof may be used as a CNT n-doping material. The compound may donate electrons spontaneously to CNTs to n-dope the CNTs, while being oxidized into its stable state. An n-doped CNT that is doped with the CNT n-doping material may maintain a stable n-doped state for a long time without being dedoped even in the air and/or water. Further, the n-doped state may be easily controlled when using the CNT n-doping material.