Carrier transport in molecularly diluted liquid crystalline photoconductor

The carrier transport properties of a molecularly diluted smectic liquid cr ystalline photoconductor, 2-(4'-octylphenyl)-6-dodecyloxynaphthalene (8-PNP -O12) and 2-(4'-hexyoxy)-6-octypbiphenyl (60-BP-8) system, were investigate d by time-of-flight technique, in order to clarify the nature of electronic conduction in the liquid crystalline mesophases. The mobility in the dilut ed liquid crystals was ambipolar, independent of both electric field and te mperature in SmA and SmB phase as in the pure 8-PNP-O12, and continuously r educed with an increase in the diluent concentration. The reduction, howeve r, remained within a small range of one third of that of pure material even in 60 mol%. The carrier transport in the diluted liquid crystals was descr ibed by the relation of a mu/rho(2) proportional to exp(-2 rho/rho(0)), whe re mu is the mobility, rho the average hopping distance, and rho(0) a wavef unction decay constant of molecular orbital, indicating the 2-dimensional r andom hopping mechanism. The fairly large rho(0) of 2.3 similar to 2.4 A ch aracterizes a fast mobility gently decreasing with an increase in the dilue nt concentration. The molecular ordering within a smectic layer did not aff ect the carrier transport properties at all except the initial difference o f the mobility, as far as comparison of those in SmB and SmB phases were co ncerned. In addition, the effect of self-organization of hopping site is di scussed in terms of carrier transport in disorded materials system.