What determines the mobility of charge carriers in conjugated polymers?

In a conjugated polymer, the mobility of charge carriers is not a well-defined coefficient of a particular material as it is in an inorganic crystalline semiconductor but depends on the time domain of detection. On a time-scale of typically 100 fs, the on-chain mobility is ultra-high and controlled by the electronic band width of the polymer chain. When a carrier hits a chain imperfection, subsequent mesoscopic on-chain motion is retarded and controlled by intrachain disorder to which the chain environment contributes. Macroscopic transport commences after a time when interchain carrier jumps become rate limiting. It is routinely probed by time-of-flight experiments and can be rationalized in terms of random walk within a rough energy landscape. Experimental signatures of the various modes of transport are discussed.