Nonsteady-state photo-EMF effect in photorefractive polymers

The nonsteady-state photo-electromotive force (photo-EMF) effect has been o bserved in photorefractive (PR) polymer films based on poly(N-vinylcarbazol e) (PVK). It was investigated in the typical tilted transmission configurat ion without and with application of moderate external direct current (dc) e lectric fields. The dependencies of the photo-EMF signals on the frequency and the amplitude of the phase modulation, the tilt angle, and the external ly applied dc field are qualitatively explained using a simple model of the effect, developed earlier for unipolar photoconductive inorganic crystals without saturation of the trapping centers. The absolute value of the photo -EMF signal was two to three times larger than expected from this model and the experimental data on conventional photoconductivity of the polymer fil m. This was rationalized considering the presence of additional space-charg e gratings appearing due to light reflectance from the rear surface of the thin-film device. (c) 1999 American Institute of Physics. [S0003-6951(99)03 423-3].