The Effect of Orientational Disorder on Hopping Conductivity in Disordered Organic Semiconductors

The model of variable range hopping is generalized to systems with extended sites. The calculation of the hopping conductivity of a disordered medium with chain structure is reduced to the percolation problem for a system of one-dimensional fragments with random distribution of lengths and orientations. The percolation problem is solved using the Monte Carlo method and the method based on the bonding criterion. The percolation threshold, which determines the dependence of the conductivity on the fragment lengths and degree of their orientational ordering (texture), is calculated. It is shown that the conductivity increases exponentially with fragment lengths and decreases with orientational ordering.