Ambipolar to unipolar irreversible switching in nanosheet transistors: the role of ferrocene in fullerene/ferrocene nanosheets

Recently, cocrystals containing organic donors and acceptors have been explored as active elements in organic field-effect transistors (FETs). Herein, we report the ambipolar charge transport properties of C-60/ferrocene (C-60/Fc) single cocrystal nanosheets. Upon heating to 150 degrees C, the ambipolar triclinic C-60/Fc nanosheet FETs were converted to n-type face-centered cubic C-60 nanosheet FETs due to the loss of ferrocene with void formation. This thermally induced transition of the crystal structure is accompanied by an irreversible switching of the semiconducting properties of the device from ambipolar to unipolar. We also elucidated the importance of the Fc for the charge transfer properties of the nanosheets using photoemission yield spectroscopy in air and theoretical calculations.