| Research Abstract |
Drift mobilities of holes and electrons in pi-conjugated macrocyclic compounds and in conductive polymers were measured successfully by use of a time-of-flight technique. It was found that hole mobilities vary up to 10 orders of magnitude, depending on the samples. In addition, mobilities of holes in sublimed films of phthalocyanine increased as a substrate temperature increased.Likewise, mobilities of holes in sublimed films of metal-free tetraphenylporphyrin increased with time. The observed increase of hole mobilities was interpreted in terms of enhanced crystallinity in the films. An increase of photocurrent quantum efficiency for H_2TPP was explained by the increased mobility, leading to suppression of electron-hole recombination.
Field and temperature dependencies of mobilities were analyzed on the basis of a disorder malism developed by Bassler. As a result, a great difference in mobility was found to reflect a difference of energetic disorder parameter, sigma, arising from the difference of steric conformations of the respective molecules. On the other hand, mu_0values were almost constant at 10^<-2>cm^2V^<-1>s^<-1>, in agreement with those observed with other molecular solids.
In conclusion, the present research reveals that one can get microscopic information on film morphology through drift mobility measurements.
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