Michael Skowrons; Drona Dahal; Pushpa Raj Paudel; Björn Lüssem

Advanced Functional Materials   34  (2023): 2303324

doi:  https://doi.org/10.1002/adfm.202303324

The gradual channel approximation forms the foundation for the analysis of field-effect transistors. It has been used to discuss transistors that are not necessarily based on the field effect as well, such as the organic electrochemical transistor (OECT). Here, the applicability of the gradual channel approximation for OECTs is studied by a 2D drift-diffusion model. It is found that OECT switching can be described by two separate effects—a doping/dedoping mechanism and the formation of an electrostatic double layer at the interface between the mixed conductor and the electrolyte. The balance between these two mechanisms is determined by the morphology of the mixed conductor, in particular the question whether ions move in the same phase and electric potential as the holes, or if separate ion and hole phases are formed. It is argued that the gradual channel approximation can only be used to describe electrostatic switching at the mixed conductor/electrolyte interface (the two-phase model), but cannot be employed to analyze devices operating on a doping/de-doping mechanism (the one -phase model). 

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