Bipolar junction formation in the case of molecular materials

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Abstract
The standard model of junction formation based on delocalized electronic levels is highly inappropriate in the case of molecular materials that are constituted of individual molecular units subsequently condensed into a material. A model is proposed to describe the electrical characteristics arising at interfaces between p‐ and n‐doped molecular materials. Two antagonistic forces will govern the amount of charge transfer giving rise to the space‐charge region (i) the driving force is given by the difference in redox potentials between the electron donor and the electron acceptor (ii) the opposite force is due to ion‐ion repulsions between ionized impurities. A numerical calculation permits the estimation of the characteristics of the space‐charge region and demonstrates that minute amounts of impurities must be present within the materials; doped insulators, therefore, cannot lead to well‐behaved devices.