Conduction mechanisms in undoped thin films of C₆₀ and C_60/70

Undoped thin films of C₆₀ and C_60/70 mixture have been electrically and optically characterized over a wide temperature range T=10...475 K. In this paper the results of the field-effect conductance, conductivity, thermoelectric power, thermoabsorption and electroabsorption measurements will be presented. The transittor studies gave an n-type behaviour, and the thermally activated field-effect conductance obeyed the Meyer-Neldel rule. The conductivity showed an activated temperature dependence above 250 K, too, but turned into a nonactivated dependence below 200 K. The results may be explained by assuming a distribution of gap states. Furthermore, we have deposited and characterized Langmuir-Blodgett films of C_60/70 and its heterostructures with poly(3-hexylthiophene).