Electrical properties of a series of carbazole polymers

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Abstract
The electrical transport properties of three vinyl carbazole polymers have been examined to determine if the observed variations in NMRchemical shifts resulting from inter−ring shielding effects could be correlated with carrier mobilities in the polymers. Drift mobilities were measured in films of the polymers overcoated with thin layers of amorphous Se using a xerographic discharge technique. Under the conditions for observing trap free space charge limited currents the hole mobilities were calculated from Child’s law. The three polymers exhibited mobilities varying as the square of the electric field over the range of fields examined. P2VK which showed the overall largest upfield shift of the aromatic protons exhibited a mobility of 1.4×10−6 cm2/V⋅sec at a field of 4×105 V/cm. PVK which exhibit an intermediate degree of shielding had a mobility of 1.4×10−7 cm2/V⋅sec and P3VK which exhibits the smallest shielding effect had a mobility of 2.4×10−8 cm2/V⋅sec both at equivalent fields. Although P2VK showed the highest mobility it also accumulated the largest amount of trapped charge. At present not enough is known about the detailed microstructure of the polymers to identify the reason for this phenomon.