Ho-Gyeong Yun

Fabrication of an Efficient Dye-Sensitized Solar Cell with Stainless Steel Substrate

Highly efficient dye-sensitized solar cells (∼8.6%) using a flexible stainless steel substrate for preparation of a mesoporous TiO 2 film electrode were fabricated by controlling the dark current density. Optimal photovoltaic properties were obtained with a cell where the TiO 2 film was coated on a Ti-isopropoxide-treated stainless steel-based substrate. The quality of the underlayer was characterized and found to be related with the photovoltaic properties.

Effect of increased surface area of stainless steel substrates on the efficiency of dye-sensitized solar cells

In order to increase the electrical contact area between TiO2 particles and stainless steel (StSt) substrates of the dye-sensitized solar cells (DSSCs), StSt foil was roughened electrochemically using sulfuric acid with some additives. Compared with the DSSC with nontreated StSt substrate, DSSC with this roughened StSt substrate showed a 33% increase in light-to-electricity conversion efficiency with negligible effect on open circuit voltage (Voc) and fill factor. Electrochemical impedance spectroscopy clearly confirmed that the increased performance was due to a decreased electrical resistance at the TiO2/StSt interface.

Widely frequency-tunable amplified feedback lasers for 10-GHz optical pulsation

Monolithic amplified feedback semiconductor lasers are demonstrated as a new solution to 10-GHz optical pulsation, where self-pulsations are generated according to the concept of a single-mode laser with shortly delayed optical feedback. They consist of a loss-coupled distributed feedback section operating as a single-mode laser and an integrated feedback cavity including a phase control, an amplifier, and a transparency section. The pulsation frequency is continuously tunable in the range of 7-11.5 GHz with an extinction ratio above 6.5 dB, which indicates that precise control of a cavity length is not needed.

Novel ionic iodide-siloxane hybrid electrolyte for dye-sensitized solar cells.

A novel ionic siloxane hybrid electrolyte was fabricated by thermal polymerization of iodide-oligosiloxane resin. The nanosized iodide-oligosiloxane was synthesized by a simple sol-gel condensation of 3-iodopropyltrimethoxysilane and diphenylsilanediol. It is found that the composition and concentration of the oligosiloxane used in the electrolyte affect the performance of the dye-sensitized solar cells (DSSCs). An optimized DSSC with the hybrid electrolyte using smaller molecular-sized oligosiloxane with a greater amount of iodide groups presented solar to electricity conversion efficiency of 5.2% at 1 sunlight (100 mW cm(-2)), which is comparable to that afforded by a liquid electrolyte.

Fast diffusion supercapacitors via an ultra-high pore volume of crumpled 3D structure reduced graphene oxide activation

In order to obtain a high performance supercapacitor, there are several factors that must be achieved including a high specific surface area (SSA), high electrical conductivity, and a high diffusion rate of the electrolyte due to an appropriate pore volume. Herein, we report a high performance supercapacitor using activated non-stacked reduced graphene oxide (a-NSrGO) that has a high SSA (up to 999.75 m2 g−1) with intrinsic high graphene conductivity (1202 S m−1) and fast diffusion of the electrolyte. Due to a high total pore volume (5.03 cm3 g−1) and a wide pore size distribution from macro- to micropores (main pore width: 0.61 – 0.71 nm) in the a-NSrGO sheets, the as-prepared a-NSrGO electrode shows high specific capacitance (105.26 F g−1) and a short relaxation time (τ0 = 1.5 s) in a propylene carbonate (PC)-based organic electrolyte. A maximum energy density of 91.13 W h kg−1 and a power density of 66 684.73 W kg−1 were estimated in a fully packaged coin cell. The high performance of the a-NSrGO supercapacitors is attributed to their specific appearance and enlarged pore distribution with high SSA.

Single-shot nanometer-scale holographic imaging with laser-driven x-ray laser

Single-shot nanometer-scale imaging techniques have become important because of their potential application in observing the structural dynamics of nanomaterials. We report here the image reconstruction results obtained using single-shot Fourier transform x-ray holography with an x-ray laser driven by a table top laser system. A minimum resolution of 87 nm was obtained from the reconstructed image. We could also discriminate the aggregates of carbon nanotubes, which shows the feasibility of single-exposure nanoimaging for real specimens using a laser-driven x-ray laser.

Cost-effective dye-sensitized solar cells consisting of two metal foils instead of transparent conductive oxide glass

A cost-effective structure for dye-sensitized solar cells (DSSCs) without using transparent conductive oxide (TCO) is reported. Instead of high-cost F/SnO(2) glass (FTO-glass) or woven metal mesh, a Ti foil and a perforation-patterned stainless steel (StSt) foil are introduced as the substrates for a counter-electrode and a photo-electrode, respectively.

Fabrication and Characteristics of 40-Gb/s Traveling-Wave Electroabsorption Modulator-Integrated DFB Laser Modules

We have developed 40-Gb/s traveling-wave electroabsorption-modulator-integrated distributed feedback laser (TW-EML) modules using several advanced technologies. First, we have adopted a selective area growth (SAG) method in the fabrication of the 40-Gb/s EML device to provide active layers for the laser and the electroabsorption modulators (EAMs) simultaneously. The fabricated device shows that the measured 3-dB bandwidth of electrical-to-optical (E/O) response reaches about 45 GHz and the return loss (S11) is kept below -10 dB up to 50 GHz. For the module design of the device, we mainly considered electrical and optical factors. The measured S11 of the fabricated 40 Gb/s TW-EML module is below -10 dB up to about 30 GHz and the 3-dB bandwidth of the E/O response reaches over 35 GHz. We also have developed two types of coplanar waveguide (CPW) for the application of the driver amplifier integrated 40 Gb/s TW-EML module, which is a system-on-package (SoP) composed of an EML device and a driver amplifier device in a module. The measured S11 of the two-step-bent CPW is below -10 dB up to 35 GHz and the measured S11 of the parallel type CPW is below -10 dB up to 39 GHz.

A quasi-solid-state dye-sensitized solar cell based on sol–gel derived in situ gelation of a siloxane hybrid electrolyte

A stable dye-sensitized solar cell (DSSC) was fabricated by a novel in situ gelation of the electrolyte. A highly condensed oligosiloxane gel was formed by sol–gel reaction of silane monomers. The oligosiloxane gel DSSC showed reduced charge recombination, and an efficiency of 5.8% with long-term stability.

Integration and Characteristics of 40-Gb/s Electroabsorption Modulator Integrated Laser Module With a Driver Amplifier and Bias Tees

Integration of a 40-Gb/s electroabsorption modulator integrated distributed feedback (DFB) laser (EML) module with a driver amplifier and bias tee was investigated. For the EML fabrication the selective area growth (SAG) technique was adopted for the first time. It is shown that, with the SAG technique, the 3-dB bandwidth of about 45 GHz was measured in the electrical to optical response, and the return loss (S11) of below -10 dB was achieved for up to 50 GHz . To integrate a bias tee within the module, a right-angle bent coplanar waveguide (CPW) was developed. The right-angle bent CPW was characterized with S11 of below - 10 dB for up to 35 GHz and insertion loss (S21) of about -1.4 dB for up to 40 GHz . The whole integrated module including the EML, a driver amplifier, and bias tee was characterized under the conditions of an operating temperature of 25degC, the modulator bias of 1.4 V, and the DFB laser current of 40 mA. S11 of below -10 dB was obtained for up to 14 GHz and the measured electrical-to-optical response has 3-dB bandwidth of about 20 GHz.