We present the enhanced photorefractive performance of high molecular weight poly(N-vinyl carbazole) (PVCz)-based composites. Higher diffraction efficiency with faster speed of grating build-up was obtained by optimizing the composition of the PVCz composites. At relatively low applied electric field of E = 45 V mu m(-1), diffraction efficiency of 26% for p-polarized probe beam and corresponding that of 5.1% for s-polarized probe beam were measured with faster grating build-up speed of 48.3 s(-1) for the composite with 2,4,7-trinitro-fluorenone (TNF) as a sensitizer. Fastest speed of grating build-up of 100 s(-1) and large optical gain up to 110 cm(-1) were measured at E = 80 V mu m(-1) for the composite with fullerene derivative of PCBM as a sensitizer. These improved performances are due to a large orientational enhancement effect with faster response speed in addition to Pockels effect for the samples with appropriate glass transition temperature. (C) 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 49: 414- 420, 2011