Yong Baek Lee

Poly(3-hexylthiophene)/multiwalled carbon hybrid coaxial nanotubes: nanoscale rectification and photovoltaic characteristics.

We fabricate hybrid coaxial nanotubes (NTs) of multiwalled carbon nanotubes (MWCNTs) coated with light-emitting poly(3-hexylthiophene) (P3HT). The p-type P3HT material with a thickness of approximately 20 nm is electrochemically deposited onto the surface of the MWCNT. The formation of hybrid coaxial NTs of the P3HT/MWCNT is confirmed by a transmission electron microscope, FT-IR, and Raman spectra. The optical and structural properties of the hybrid NTs are characterized using ultraviolet and visible absorption, Raman, and photoluminescence (PL) spectra where, it is shown that the PL intensity of the P3HT materials decreases after the hybridization with the MWCNTs. The current-voltage (I-V) characteristics of the outer P3HT single NT show the semiconducting behavior, while ohmic behavior is observed for the inner single MWCNT. The I-V characteristics of the hybrid junction between the outer P3HT NT and the inner MWCNT, for the hybrid single NT, exhibit the characteristics of a diode (i.e., rectification), whose efficiency is clearly enhanced with light irradiation. The rectification effect of the hybrid single NT has been analyzed in terms of charge tunneling models. The quasi-photovoltaic effect is also observed at low bias for the P3HT/MWCNT hybrid single NT.

Surface enhanced Raman scattering effect of CdSe/ZnS quantum dots hybridized with Au nanowire

Functionalized CdSe/ZnS quantum dots (QDs) were attached to the surface of Au nanowire (NW). Analysis of optical absorption spectra disclosed surface plasmon bands of Au NWs at 562 and 627 nm and showing an overlap with the QD absorption band. Micro Raman spectra (λex = 514 nm) of the QDs/Au single NW exhibited surface enhanced Raman scattering (SERS) peaks at 180, 205, and 277 cm−1, corresponding to surface, longitudinal, and transverse optical phonon modes, respectively. From time-resolved fluorescence spectra, the exciton lifetime of QDs decreased after hybridization with Au NW due to the energy transfer, supporting the SERS effect.

Tuning optical properties of poly(3-hexylthiophene) nanoparticles through hydrothermal processing

Abstract Poly(3-hexylthiophene) (P3HT) nanoparticles (NPs) were prepared by a reprecipitation method. Hydrothermal processing applied external pressure to the pristine P3HT NPs at temperatures ranging from 60 to 150 °C. Optical absorption and photoluminescence (PL) spectra for the hydrothermally treated P3HT NPs varied markedly with the processing temperature. With increasing treatment temperature, the absorption peak broadened and the peak position shifted from 510 to 623 nm; moreover, the intensity ratio of the 0–1 to 0–0 emission varied. These changes were caused by interactions between the P3HT main chains and alkyl side groups and conformational modifications induced by the high pressure during the hydrothermal process. The evolution of the optical absorption spectra of the P3HT NPs during the hydrothermal processing was strongly correlated with the variation of PL excitation spectra and with the PL emission spectra of a single NP.

Nanoscale luminescence characteristics of CdSe/ZnS quantum dots hybridized with organic and metal nanowires: Energy transfer effects

Hybrid nanosystems comprising functionalized CdSe/ZnS core–shell quantum dots (QDs) on the surface of light-emitting poly(3-hexylthiophene) (P3HT), metallic copper (Cu), and insulating polystyrene (PS) nanowires (NWs) are fabricated. Using high-resolution scanning transmission electron microscopy, we observe that the QDs are attached to the surface of the NWs. The nanoscale photoluminescence (PL) characteristics of the hybrid QD/P3HT, QD/Cu, and QD/PS single NWs are investigated using laser confocal microscopy (LCM) with high spatial resolution. For the hybrid QD/P3HT single NW, the LCM PL intensity from the P3HT NW increases considerably, while that of the QDs decreases due to Forster resonance energy transfer. Hybridization affects the nanoscale PL characteristics of both the P3HT NW and the QDs. The LCM PL intensity of the hybrid QD/Cu NW is three times higher than that of the QD/PS NW, because of surface plasmon resonance coupling energy transfer between the QDs and the Cu NW. Time-resolved PL spectra reveal that the exciton lifetimes of the QDs drastically decrease after the hybridization with P3HT or Cu NWs, due to energy transfer effects. The nanoscale PL efficiency of the QDs can be controlled by hybridization with NWs having distinct properties.

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.