Influence of chromophore content on the steady-state space charge formation of poly[methyl-3-(9-carbazolyl) propylsiloxane]-based polymeric photorefractive composites

We investigate the influence of chromophore content on the steady-state space charge formation. The chromophore is expected to act as a trap for hole transport in the matrix when the chromophore has a lower ionization potential as compared with the hole transporting material. We measured the photoconductivity and space charge field and then discussed their chromophore content dependence. At low chromophore concentrations, the photoconductivity decreased with increasing chromophore content due to the trap effect of chromophore. Above 3 wt % of chromophore concentration, however, the photoconductivity increased with the chromophore content through the increment of hole detrapping and the decrement of electron-hole recombination. The space charge field, which is dependent on the mobile hole and trap densities, increased with the chromophore content and saturated at about 15 wt % of chromophore. Numerical simulation work, the modified Schildkraut differential equation, was used to help us understand the experimental results. All experimental results are in excellent agreement with the simulation predictions.