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 inves tigated as a function of both dopant level and time. This oligothiophe ne was doped in solution with various types of organic and inorganic o xidizing agents. The solutions were stable for days, yielding excellen t processability. Smooth coherent films could be spun from these solut ions. The conductivity varied with dopant concentration between 4.10(- 9) S/cm for the unintentionally doped oligomer upto 20 S/cm at the hig hest doping levels. The conductivity was found to be a universal funct ion of dopant concentration. This dependence is explained in terms of a hopping type conductivity mechanism. The deterioration of the conduc tivity with time depends on the doping level. This is quantitatively e xplained assuming a first order Arrhenius equation for the decay of do pant ions, combined with the dependence of conductivity as a function of dopant content.