Characterization of Carrier Transport and Trapping in Photorefractive Polymer Composites Using Photoemission Yield Spectroscopy in Air

Abstract

Carrier trapping in organic photorefractive (PR) composites is affected by the bulk state (which can be varied by modifying the molecule structure and processing method used) and the presence of dipolar molecules. Such situations complicate the understanding of carrier trapping in PR composites. The density of states (DOS) provides direct information about carrier trapping in materials. Here, the first attempt to directly measure the DOS in PR composites is performed to investigate the effect of the change of the bulk state on carrier trapping. The distribution of the DOS is measured using photoemission yield spectroscopy in air. The bulk state of the PR composites is tuned based on the crystallization of dipolar nonlinear optical dyes included as a component. Thus, the bulk with a different net dipole (spatially averaged dipole) moment is prepared with the same composition as the PR materials. The edge part of the DOS profile clearly changes upon tuning the bulk state. The diminished net dipole moment achieved by the bulk state tuning causes the suppression of carrier trapping, which is well supported by the dipole trapping model. This result coincides with those obtained using photocurrent and PR grating measurements.

Flexible All-Organic Photorefractive Devices

“…Organic photorefractive (PR) polymers have wide potential for updatable holographic imaging and dynamic holographic displays. Dynamic holography is the ultimate in three-dimensional (3D) imaging and is expected to be key technology for a next-generation display system. − Photorefractive phenomena are based on refractive index modulation derived from the distributed space-charge field through the Pockels (first-order optical nonlinearity) effect. − Since the first study of organic photorefractive polymers was reported, numerous research investigations have focused on PR polymers. − ,− …”

Photorefractive hyper-structured molecular glasses constructed by calix[4]resorcinarene core and carbazole-based methine nonlinear optical chromophore

“…Among various organic PR materials, gust-host systems, prepared by doping small molecular NLO chromophores into polymeric photoconductors, are the most studied for practical application because of their eases of fabrication. [7,8] However, with the increasing of NLO chromophore doping concentration, the unfavorable antiparallel packing of chromophores resulting from the strong interchromophore dipole-dipole interactions gradually appeared, leading to a decreased PR effect. [9] Recently, some nonlinear molecules such as hyper-structured molecules (HSMs), [10] star-shaped molecules, [11] dendritic molecules, [12] etc.…”