Polarized emission of oriented semiconductor nanorods in light-emitting application

Abstract

The semiconductor nanorods (NRs), which are emerging as one of the important materials in the field of nanotechnology due to their unique properties such as efficient charge transport and linear polarization emission characteristics, are not yet utilized in electric field devices. In order to utilize the unique properties of NRs in an ensemble film, a long-range unidirectional oriented film is absolutely necessary. Unidirectional orientation of NRs has been achieved by controlling the interparticle attraction in a local area. In this study, uniaxial orientation of NRs in the uniform thin film forming process was studied to utilizing the anisotropic optical properties of NRs in a display device. Based on the understanding of the interparticle forces in the thin film forming mechanism, it became possible to manufacture a nanorod polarizing film that can be directly applied to an electroluminescent device by controlling the depletion factor in the solution and the evaporation retardation of the film. Even in the rapid formation of a uniform thin film, the formation and growth of the stacking unit of the NRs could be controlled by controlling the attractive force between the NRs confirmed by the polarization characteristics. The NRs large-area orientation film was directly applied to the emitting layer of the light emitting device (NR-LED), showing improved efficiency of linear polarized filter transmission and an increase in external quantum efficiency through controlling the balance of charge injection. In an electroluminescent device that adjusts the intensity of light by current density itself, a circular polarized filter is used for reducing the surface reflectance with respect to an external light. When NRs with chiral active ligands were assembled by interparticle attraction, the emissive film emit circularly polarized emission by forming a helical unit of NRs. The circularly polarized emission was reinforced with the large-area oriented NRs using the evaporation retardation effect. Improved the transmittance of circularly polarized filter without introducing any additional optical layer is expected to solve the problem that of the mobile display decrease in luminance through the polarizer, and to reduce the power consumption. The long-range unidirectional orientation of nanorods by controlling the interactions between the nanorods that occur in the solution process confirmed that the self-assembly control, which was possible at the existing air/solution interface, can be applied to the device. At this time, by controlling the stacking units of the arranged nanorods in a linearly assembled form or a helically assembled form, linear or circularly polarized characteristics could be observed in the ensemble film.