Low voltage operating OFETs based on solution-processed metal phthalocyanines

The class of sodium salts of sulphonated metal phthalocyanines (MePCS (x) , S = SO3Na, x=1-4) was investigated as a p-type channel component in organic field-effect transistors (OFETs). The solubility of these materials appears to be enhanced compared to their non-sulphonated counterparts (MePCs). We fabricated transistors based on MePCSx varying the central metal atom (Me = Ni, Co, Zn, Al) and we evaluated the dependence of transistor performance on the nature of the central atom and the degree of sulphonation. The best results were obtained in the case of Ni and low sulphur content. In this case the mobility value is mu=1.08 cm(2) V-1 s(-1) and the on/off current ratio similar to 10(3). The degree of sulphonation affects the electric field inside the active film in a way analogous to the case of polyelectrolyte-gated OFETs. The Na+ counter ions present in the channel contribute to the device characteristics but their concentration should be controlled in order to optimize device performance.