Comparison of new photorefractive composites based on a poly(phenylene vinylene) derivative with traditional poly(n-vinylcarbazole) composites

The performances of two classes of photorefractive polymer composites with low glass-transition temperatures (about 10-5 °C) are compared. One is based on the commonly used photoconductor poly(N-vinylcarbazole) (PVK), i.e., containing isolated charge-transport moieties for hopping. The other is based on the π-conjugated poly[1,4-phenylene-1,2-di(4-benzyloxyphenyl)vinylene] (DBOP-PPV), promising faster response times. The steady-state performance of the DBOP-PPV-based composites was found to be superior owing to (i) the larger internal free volume, allowing more efficient poling of the chromophores, and (ii) the slightly stronger space-charge field as a result of an increased trap density. By contrast, the dynamic response in a four-wave mixing experiment was similar to that of PVK-based composites despite the higher hole-drift mobility in conjugated PPV homopolymers than PVK. It was demonstrated that this is mainly a result of the poor charge-carrier generation efficiency