om ers ▁or ▁segments ▁of ▁a ▁conjug ated ▁polym er ▁chain ▁and ▁move ▁by ▁in co her ent ▁ho pping ▁among ▁adjacent ▁sites ▁with ▁statist ically ▁variable ▁energ ies . ▁Qu ite ▁often ▁the ▁site ▁energ ies ▁feature ▁a ▁Gaussian ▁distribution . ▁Also ▁the ▁ho pping ▁distances ▁can ▁vary ▁statist ically ▁( pos itional ▁dis order ). ▁A ▁consequence ▁of ▁the ▁ener get ic ▁bro aden ing ▁of ▁the ▁density ▁of ▁states ▁( D OS ) ▁distribution ▁is ▁that ▁charge ▁motion ▁is ▁both ▁temperature ▁and ▁field ▁dependent ▁and ▁the ▁charge ▁car rier ▁mob ility ▁can ▁be ▁several ▁orders ▁of ▁magnitude ▁lower ▁than ▁in ▁an ▁equivalent ▁cry st all ine ▁system . ▁This ▁dis order ▁effect ▁on ▁charge ▁car rier ▁motion ▁is ▁dimin ished ▁in ▁organ ic ▁field - effect ▁trans ist ors ▁because ▁current ▁flow ▁is ▁conf ined ▁in ▁a ▁thin ▁layer . ▁Therefore , ▁the ▁tail ▁states ▁of ▁the ▁D OS ▁distribution ▁are ▁already ▁filled ▁so ▁that ▁the ▁activation ▁energy ▁for ▁charge ▁car rier ▁ho pping ▁is ▁dimin ished . ▁For ▁this ▁reason ▁the ▁charge ▁car rier ▁mob ility ▁infer red ▁from ▁F ET ▁experiments ▁is ▁always ▁higher ▁than ▁that ▁determined ▁from ▁TO F ▁experiments . ▁ ▁In ▁organ ic ▁sem icon duct ors ▁charge ▁carri ers ▁couple ▁to ▁v ibr ational ▁modes ▁and ▁are ▁referred ▁to ▁as ▁polar ons . ▁Therefore , ▁the ▁activation ▁energy ▁for ▁ho pping ▁motion ▁contains ▁an ▁additional ▁term ▁due ▁to ▁struct ural ▁site ▁relax ation ▁upon ▁charg ing ▁a ▁mole cular ▁entity . ▁It ▁turns ▁out