Electron transport in semiconducting polymers is usually inferior to hole transport, which is ascribed to charge trapping on isolated defect sites situated within the energy bandgap. However, a general understanding of the origin of these omnipresent charge traps, as well as their energetic position, distribution and concentration, is lacking. Here we investigate electron transport in a wide range of semiconducting polymers by current–voltage measurements of single-carrier devices. We observe for this materials class that electron transport is limited by traps that exhibit a Gaussian energy distribution in the bandgap. Remarkably, the electron-trap distribution is identical for all polymers considered: the number of traps amounts to 3 × 1023 traps per m3 centred at an energy of ~3.6 eV below the vacuum level, with a typical distribution width of ~0.1 eV. This indicates that the electron traps have a common origin that, we suggest, is most likely related to hydrated oxygen complexes. A consequence of this finding is that the trap-limited electron current can be predicted for any polymer.
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The authors thank M. Lenes, Y. Zhang, M. Mandoc and M. Lu for their contributions to this work and J. Harkema for technical support. The work at the University of Groningen was supported by the European Commission under contract FP7-13708 (AEVIOM). The work at Georgia Tech was supported by the MRSEC Program of the National Science Foundation under Award Number DMR-0819885.
The authors declare no competing financial interests.
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Nicolai, H., Kuik, M., Wetzelaer, G. et al. Unification of trap-limited electron transport in semiconducting polymers. Nature Mater 11, 882–887 (2012). https://doi.org/10.1038/nmat3384
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