AN INVESTIGATION OF THE ELECTRONIC-PROPERTIES OF POLY(4,4'-DIPENTOXY-2,2'-BITHIOPHENE)

A study of the electronic properties of a polythiophene (poly(4,4'-dip entoxy-2,2/-bithiophene) as functions of the positive doping level has been carried out. The oxidative cyclic voltammogram and the electron spin resonance (ESR) spectrum show the consecutive formation of polaro n and bipolaron states on increasing the doping level of the polymer. From the optical spectra it was found that the pi-pi band undergoes a blue shift with the doping. The Fermi level of the polymer was derive d from the diffusion potential of the heterojunction between n-doped s ilicon and poly(4,4'-dipentoxy-2, 2'-bithiophene). As expected for p-t ype inorganic semiconductors, the Fermi level was found to be pushed t owards the valence band by increasing the doping level. The trend of t he experimental Fermi level is in good agreement with the one calculat ed for a p-type semiconductor with the same doping level and bandgap a s those of poly(4,4'-dipentoxy-2,2'-bithiophene).