We demonstrate that the electron transport in conjugated polymers as poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV) is limited by deep traps that mask the intrinsic transport properties of free electrons in these materials. These traps can be deactivated by addition of the $n$-type dopant decamethylcobaltocene (DMC). By filling the traps with electrons from the DMC donor a trap-free space-charge limited electron current can be obtained in MEH-PPV, enabling a direct measurement of the free-electron mobility. We demonstrate that the electron mobility is equal to the hole mobility with an identical temperature dependence, showing that the charge transport in conjugated polymers is intrinsically balanced.

• Received 23 November 2009

DOI:https://doi.org/10.1103/PhysRevB.81.085201