Improvement of Photorefractivity in PVK Based Composite by Doping of Graphene

The effect of graphene was investigated on photorefractivity in the composite consisting of hole transporting poly(N -vinyl carbazole) (PVK) (44.5 wt%), electro-optically active 4-(azepan-1-yl) benzylidenemalononitrile (7-DCST) (35.0 wt%), plasticizing dibutyl phthalate (DBP) (20.0 wt%), and photosensitizing fullerene (C60) (0.5 wt%) by changing the amount of graphene from 0 to 0.1 wt% and monitoring the two beam coupling gain coefficient. It is found that the gain coefficient drastically increased by the addition of graphene and reached maximum at the content of around 0.005-0.007 wt% (e.g., it was 112 cm-­1 at 41.7 V/μm at 0.005 wt%). Beyond the maximum, the gain coefficient went through the local minimum value at around 0.05 wt%, and then gradually increased till 0.1 wt%. These results suggested that at the lower content, graphene worked as trap sites, and at the higher content, the nature of trap sites was changed by the onset of the overlap of graphene sheets.