Photorefractive Performances, Photoconductive Properties, and Transient Dynamics of Photocurrent for Poly‐TPD Polymer Composites

ABSTRACT The photorefractive (PR) performances, photoconductivity, and transient dynamics of photocurrent are investigated for poly[ N , N ’‐bis(4‐butylphenyl)‐ N , N ’‐bis(phenyl)‐benzidine] (poly‐TPD)‐based PR composites. Plasticizer and sensitizer are benzyl butyl phthalate (BBP) and [6,6]‐phenyl C 61 butyric acid‐methyl ester (PCBM), respectively. Five different types of amino‐styrene‐based NLO dyes are compared from compatibility and PR performance points of view. The proper choice of NLO dye is 4‐azacycloheptylbenzylidene malononitrile (7‐DCST). The electric field E and the illumination wavelength dependences of the diffraction efficiency η and the response time τ η are investigated. η of 6.85% with τ η of 3.8 ms and optical gain of 42.3 cm −1 are measured at 532 nm with E = 80 V µm −1 for poly‐TPD/7‐DCST/BBP/PCBM. The saturation space‐charge field, the effective number density of traps, the space‐charge field, and the PR phase shift are evaluated. The time for trapping directly evaluated from the photoconductivity is significantly related to τ η . The simulation of the transient dynamics of photocurrent reproduced well the shallow trapping at earlier time regions, followed by the deep trapping at later times, which is well correlated to the growth of η . The origin of the shallow and deep traps is discussed.