Researchers in High Magnetic Field Laboratory, Chinese Academy of Science (CHMFL) in Hefei prepared film and array-arranged single crystalline nanorod (NR) of perylene-3,4,9,10-tetracarboxylic dianhydride (PTCDA) by organic molecular beam deposition method, and investigated the photophysical properties of the film and NR array as well as the electrical characteristics of single NR.

Owing to weak intermolecular forces (i.e. π-π interaction, charge-transfer interaction, van der Waals force and H-bands), organic semiconductor could possess many unique advantages such as good processability, high reactivity and flexibility. Attribute to the above advantages, organic semiconductors are complementary to their inorganic counterparts and are widely applied in the fabrications of modern optoelectronic devices, for instance, organic light-emitting diodes, organic field-effect transistors and organic solar cell. Yet, the achievement of enhanced absorbance and luminescence as well as the increment of electrical property still remain challenges.

Herein, the researchers demonstrate that the π*–π transition and the intermolecular charge-transfer transition arouse the strong photoluminescence (PL) emission in the visible region. The strong π–electrons interaction between molecular stacks induces the optical waveguide feature of PTCDA NRs.

Moreover, when the electrical field plane of the incident light is parallel to the molecular plane, absorption enhancement occurs. The high degree of crystallinity, the optical waveguide features, and the vertical growth of the PTCDA NRs can result in enhanced Frenkel emission along the growth direction of the PTCDA NRs.

Specifically, they measure the electrical conductivity along the growth direction of single NR, which is roughly 0.61 S·m^–1 (much higher than that of pure crystalline PTCDA films), and demonstrate that the current versus voltage (I-V) characteristic of PTCDA NR still present good repeatability even when the working electrical field intensity and current density are as high as 1.58×10⁷ V·m^-1 and 5.17×10⁶ A·m^-2 respectively.

The above results could be served as the experiment guidance for the fabrication and performance enhancement of the miniature organic optoelectronic devices.

This work entitled Photophysical and electrical properties of organic waveguide nanorods of perylene-3,4,9,10-tetracarboxylic dianhydride performed by Dr. HAN Yuyan in TIAN Mingliang’s group at CHMFL was published online in Nano Research. And the work was supported by the National Natural Science Foundation of China, and the program of Users with Excellence, Hefei Science Center of Chinese Academy of Sciences.

Figure 1 (a) SEM image of a single NR with Pt-electrodes deposited by focus ions beam deposition techniques. (b) I-V curves of PTCDA NR on SiO2 dielectric layer. Figure (a) is located in the marked part in Figure 5 (b) inset which is the optical image of the device. (Image by HAN Yuyan)