By Josh Perry, Editor
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Researchers from the Dresden (Germany) Integrated Center for Applied Physics and Photonic Materials (IAPP) and the Center for Advancing Electronics Dresden (cfaed) at TU Dresden, along with Stanford University (Palo Alto, Calif.) and the Institute for Molecular Science (Okazaki, Japan), identified the parameters that influence electrical conductivity in doped organic semiconductors.

Illustration of an organic semiconductor layer (green molecules) with dopant molecule (purple). (Sebastian Hutsch, Frank Ortmann/TU Dresden)

Doping the integrated circuits, according to a report from TU Dresden, allows scientists to control the behavior of semiconductor materials, but it was unknown how the transport mechanisms of charges in doped organic semiconductors worked and how they were unable to match the performance of silicon.

Researchers discovered that doping creates groupings of two oppositely-charged molecules. “The properties of these complexes like the Coulomb attraction and the density of the complexes significantly determine the energy barriers for the transport of charge carriers and thus the level of electrical conductivity,” the article explained.

By understanding how the transport mechanism works, researchers believe that new organic semiconducting materials can be created that will have higher conductivity.

The research was recently published in Nature Materials. The abstract stated:

“Doped organic semiconductors typically exhibit a thermal activation of their electrical conductivity, whose physical origin is still under scientific debate.

“In this study, we disclose relationships between molecular parameters and the thermal activation energy (E_A) of the conductivity, revealing that charge transport is controlled by the properties of host–dopant integer charge transfer complexes (ICTCs) in efficiently doped organic semiconductors.

“At low doping concentrations, charge transport is limited by the Coulomb binding energy of ICTCs, which can be minimized by systematic modification of the charge distribution on the individual ions. The investigation of a wide variety of material systems reveals that static energetic disorder induced by ICTC dipole moments sets a general lower limit for E_A at large doping concentrations.

“The impact of disorder can be reduced by adjusting the ICTC density and the intramolecular relaxation energy of host ions, allowing an increase of conductivity by many orders of magnitude.”