Jin Woo Lee

Anisotropic optical absorption of organic rubrene single nanoplates and thin films studied by μ-mapping absorption spectroscopy

Local absorption spectra and absorption coefficients were obtained from organic rubrene single nanoplates. Absorption along the b-axis was higher than along the a-axis for polarized illumination on an ab-faced single-crystal rubrene nanoplate, and the lowest crystal transition peak (∼530u2009nm) relatively increased in size with an increasing incidence angle due to the anisotropic absorption strength along the crystal axes. Rubrene thin films grown by organic molecular beam deposition displayed microscopically varying absorption spectra; the relative peak height of the M-polarized band and the overall absorption strength were strongest with polarized illumination along the c-axis.

Electrospinning and optical characterization of organic rubrene nanofibers

We report on the preparation of continuous organic rubrene nanofibers using the electrospinning method. We added the minimal amount of poly (ethylene oxide) in the electro-spinning solution to provide the viscosity required for electrospinning. Optical characteristics such as absorption, photoluminescence, and Raman spectra all confirmed the successful formation of rubrene nanofibers. Confocal Raman spectra obtained from single rubrene nanofibers showed co-existence of the amorphous and the crystal phase of the rubrene molecule. We also demonstrated that our rubrene nanofibers can be used as efficient optical waveguides. Our result suggests that abundant fluorescent, continuous nanofibers of small molecule materials can be successfully prepared using electrospinning.

Electrical characteristics of organic perylene single-crystal-based field-effect transistors

We report on the fabrication of organic field-effect transistors (OFETs) using perylene single crystal as the active material and their electrical characteristics. Perylene single crystals were directly grown from perylene powder in a furnace using a relatively short growth time of 1–3 h. The crystalline structure of the perylene single crystals was characterized by means of a single-crystal x-ray diffractometer. In order to place the perylene single crystal onto the Au electrodes of the field-effect transistor, a polymethlymethacrylate thin layer was spin-coated on top of the crystal surface. The OFETs fabricated using the perylene single crystal showed a typical p-type operating mode. The field-effect mobility of the perylene crystal based OFETs was measured to be ∼9.62×10−4u2002cm2/Vu2009s at room temperature. The anisotropy of the mobility implying the existence of different mobilities when applying currents in different directions was observed for the OFETs, and the existence of traps in the perylene crystal...

Copper-phthalocyanine based organic thin film transistor

Copper-phthalocyanine based organic thin film transistors (OTFTs) were fabricated. Cu-Pc thin films as an active layer were deposited onto the SiO2 layer as a gate insulator by using organic molecular beam deposition system. The OTFT devices showed p-type characteristics with field-effect mobility and threshold voltage as 1.22x10-3 cm2/Vsand -40 V, respectively. The activation energy was estimated to be 0.073 eV, through the temperature dependence of carrier mobility.

Single nanoparticle of organic p-type and n-type hybrid materials

We fabricated hybrid nanoparticles (NPs) of p-type poly(3-hexylthiophene) (P3HT) and n-type fullerene derivative {[6,6]-phenyl C61-butyric acid methyl ester (PCBM)} materials through a mini-emulsion method. The nanoscale photoluminescence (PL) characteristics of the non-annealed and annealed hybrid single NPs with different concentrations of P3HT and PCBM were investigated using a laser confocal microscope (LCM) with high spatial resolution. The luminescence characteristics corresponding to the P3HT and PCBM materials were observed simultaneously in the LCM PL spectra for P3HT/PCBM hybrid NP after the annealing process. We propose that the annealing process for the hybrid NPs assisted the ordering of P3HT main chains and the formation of PCBM domains through the gathering of the molecules, indicating nanoscale phase separation. This was supported by UV-Vis absorption and Raman spectroscopy results. Conducting atomic force microscope experiments on an annealed hybrid single NP allowed for the measurement of the characteristic photoresponsive current–voltage curves, and monochromatic photovoltaic characteristics and the avalanche photodiode effect were observed in the low- and high-bias regions, respectively.