Chemical structure of the investigated polyspirobifluorene copolymers. The compositions of polymer 1 (polyspirobifluorene anthracene) are and whereas it for polymer 2 (polyspirobifluorene carbazole) and .
Representative TOF transients for polymer 1 (polyspirobifluorene anthracene) at , , , and at constant electric field. A cusp develops at higher temperatures. At lower temperatures, the tail of the transient signal lengthens, a signature of dispersive transport.
Hole mobility of polymer 1 as a function of in semilogarithmic representation at a selection of temperatures. The lines are fits to the experimental data.
The field dependence of hole mobility of polymer 2 for a selection of temperatures in a semilogarithmic plot.
The zero-field hole mobility plotted vs in a semilogarithmic fashion. Notice the change of slope as the transport becomes dispersive.
The extrapolated zero-field mobilities as a function of for polymer 2. The lines are linear fits to the data. Notice the transition to the dispersive transport regime below indicated by the change of slope.
Representation of the energetic situation of the DOS at room temperature (1) and at a higher temperature (2) assuming a constant energy of injection . In case (1) the holes are injected close to their equilibrium energy . Transport of charges can occur immediately. In case (2) the holes are injected into the tail of the occupied density of states (ODOS); therefore, they have to reach the transport sites closer to the center of the ODOS before transport can occur. This process may cause the cusp that can be observed at higher temperatures.
Charge-carrier transport parameters of polymers 1 and 2.
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