Study on the Mechanism of Electron and Hole Transport in Organic Light-Emitting Diodes and Material Design for Novel Materials

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Vibronic coupling constants of the carrier-transporting molecules employed in organic light-emitting diodes are evaluated using the molecular orbital and density functional methods. The results are analyzed on the basis of a concept of vibronic coupling density. They suggest that it is possible to suppress vibronic coupling for electron-density difference to be localized on atoms and to be symmetrically distributed. This design principle can lead us to carrier-transporting molecules with high mobility and low power consumption. In addition, it is shown that electron-hole or electron-electron interactions play crucial role in electron-density differences. Based on the design principle, novel hole- and electron-transporting molecules are proposed. Calculations of their vibronic couplings and non-equilibrium Green's function indicate that they are expected as a highly-efficient carrier-transporting molecule.