STABLE-SOLUTIONS OF DOPED THIOPHENE OLIGOMERS

The electrical conductivity of alpha, alpha' - coupled dodecathiophene substituted with four dodecyl side chains, T12d4(2,5,8,11), was investigated as a function of both dopant level and time. This oligothiophene was doped in solution with various types of organic and inorganic oxidizing agents. The solutions were stable for days, yielding excellent processability. Smooth coherent films could be spun from these solutions. The conductivity varied with dopant concentration between 4.10(-9) S/cm for the unintentionally doped oligomer upto 20 S/cm at the highest doping levels. The conductivity was found to be a universal function of dopant concentration. This dependence is explained in terms of a hopping type conductivity mechanism. The deterioration of the conductivity with time depends on the doping level. This is quantitatively explained assuming a first order Arrhenius equation for the decay of dopant ions, combined with the dependence of conductivity as a function of dopant content.