n-type doping of organic thin films using cationic dyes

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 x 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.