n-Type Doping of Organic Thin Films Using Cationic Dyes


  • We acknowledge support from the Graduiertenkolleg “Sensorik”, funded by the Deutsche Forschungsgemeinschaft, and from the German Secretary for Education and Research (BMBF). Part of the investigations was supported by the Leibnitz prize from the Deutsche Forschungsgemeinschaft. We thank N. R. Armstrong (Tucson, Arizona), T. Fuhrmann (Kassel), H. Hartmann (Merseburg), and N. Karl (Stuttgart) for useful discussions.


We present an approach to stable n-type doping of organic matrices using organic dopants. In order to circumvent stability limitations inherent to strong organic donors, we produce the donor from a stable precursor compound in situ. As an example, the cationic dye pyronin B chloride is studied as a dopant in a 1,4,5,8-naphthalene tetracarboxylic dianhydride (NTCDA) matrix. Conductivities of up to 1.9 × 10–4 S cm–1 are obtained for doped NTCDA, two orders of magnitude higher than the conductivity of NTCDA doped with bis(ethylenedithio)-tetrathiafulvalene as investigated previously, and four orders of magnitude higher than nominally undoped NTCDA films. Field-effect measurements are used to prove n-type conduction and to study the doping effect further. The findings are interpreted using a model of transport in disordered solids using a recently published model. Combined FTIR, UV-vis, and mass spectroscopy investigations suggest the formation of leuco pyronin B during sublimation of pyronin B chloride.