Donggun Lim

Simple Microwave-Assisted Synthesis of Amphiphilic Carbon Quantum Dots from A3/B2 Polyamidation Monomer Set

Highly fluorescent and amphiphilic carbon quantum dots (CQDs) were prepared by microwave-assisted pyrolysis of citric acid and 4,7,10-trioxa-1,13-tridecanediamine (TTDDA), which functioned as an A3 and B2 polyamidation type monomer set. Gram quantities of fluorescent CQDs were easily obtained within 5 min of microwave heating using a household microwave oven. Because of the dual role of TTDDA, both as a constituting monomer and as a surface passivation agent, TTDDA-based CQDs showed a high fluorescence quantum yield of 29% and amphiphilic solubility in various polar and nonpolar solvents. These properties enable the wide application of TTDDA-based CQDs as nontoxic bioimaging agents, nanofillers for polymer composites, and down-converting layers for enhancing the efficiency of Si solar cells.

CuInSe 2 solar cells prepared by using seleno-amide as selenium source

CuInSe2 (CISe) absorber films were prepared by selenizing Cu-In metallic films with seleno-amide in a tube furnace for solar cell fabrication. Seleno-amide used in this study is stable at room temperature and decomposes into H2Se at below 150 °C. Chalcogen amides allow safe transportation and the handling of chalcogen sources that can produce chalcogen hydrides at reasonably low temperature. Post-selenization annealing at 500°C for various time periods were carried out to reverse the indium inhomogeniety created during selenization and to promote further phase transformation. Cu/In ratio of CISe thin films was reduced from ~1.6 down to ~0.9 through the post-selenization annealing at 500°C for up to 3 hours. The first batch of cells fabricated with soda-lime glass/Mo/CISe/CdS/ZnO/ZnO:Ga structure exhibited power conversion efficiency up to 1.6% without any optimization.

Improvement of Etch Rate and Profile by SF 6 , C 4 F 8 , O 2 Gas Modulation

Deep trench etching of silicon was investigated as a function of RF source power, DC bias voltage, gas flow rate, and gas addition. On increasing the RF source power from 300 W to 700 W, the etch rate was increased from to . The addition of gas improved the etch rate and the selectivity. The highest etch rate is achieved at the gas addition of 12 %, The selectivity to PR was 65.75 with gas addition of 24 %. At DC bias voltage of -40 V and gas flow rate of 30 seem, We were able to achieve etch rate as high as with good etch profile.

Influence of Sputter Power on the Structural and Optical Properties of CdS Films for Photovoltaic Applications

CdS films have been prepared on polycarbonate, polyethylene terephthalate, and Coming 7059 substrates by r.f magnetron sputtering technique at room temperature. A comparison of the properties of the films deposited on polymer and glass substrates was performed. In addition, the influence of the sputter power on the structural and optical properties of these films was evaluated. The XRD measurements revealed that CdS films were polycrystalline and retained the mixed structure of hexagonal wurtzite and cubic phase, regardless of substrate types. As the sputter power was increased from 75 to 150 Watt, the structure of CdS films was converted from the mixed of hexagonal and cubic phase to hexagonal phase. The morphology of CdS films is found to be continuous and dense. Also, the grain of CdS films is larger with increasing the sputter power. The average transmittance exceeded 80 % in the visible spectrum for all films and decreases slightly with the sputter power.

A Study on Properties of ZnO:Al Films on PC Substrate for Solar Cell Applications

Al doped ZnO thin films (ZnO:Al) were deposited on poly carbonate (PC) substrate by rf magnetron sputtering. In addition, the electrical, optical properties of the films prepared at various conditions were investigated. As the sputter power increased, the resistivity of ZnO:Al films decreased, regardless of substrate types. However, the resistivity of the films increased with the sputter pressure. The ZnO:Al films were increasingly dark gray colored as the sputter power increased, resulting in the loss of transmittance. High quality films with resistivity as low as 1.4310 Ω-cm and transmittance over 80 % have been obtained by suitably controlling the deposition parameters.

N2 Plasma Treatment Effects of SiNx Buffer Layer for Low Temperature Process

To adopt thin film transistor (TFT) type FRAM, low temperature process is necessary. SiNx has good properties and advantages as a low temperature processed buffer layer. The SiNx films were grown on the p-Si(100) substrate by the transformer coupled plasma chemical vapor deposition (TCP-CVD). By employing N2 plasma treatment, interface traps such as mobile charges and injected charges were removed, hysteresis of capacitance-voltage (C-V) curve disappeared. After N2 plasma treatment, a leakage current was decreased about 2 orders. The memory window of low temperature processed (at 550°C) metal-ferroelectric-insulator-silicon (MFIS) capacitor was as large as about 1.5 V.

Improvement of Dielectric and Interface Properties of CeO2 Buffer Layer by Using the Metal Seed Layer and N2 Plasma Treatment

In this paper, we investigated the feasibility of cerium oxide (CeO2) films as buffers layer of MFIS (metal ferroelectric insulator semiconductor) type capacitors. CeO2 layer were prepared by a two-step process of a low temperature film growth and subsequent RTA (rapid thermal annealing) treatment. By applying a cerium (Ce) metal seed layer of 4 nm, unwanted SiO2 layer generation was successfully suppressed at the interface between the buffer layer and the Si substrate. After N2 plasma treatment, the leakage current was reduced by about 2-orders. By employing a N2 plasma treatment, we were able to successfully obtain good properties at the interface between the buffer layer and the Si substrate.

The Analysis on the Effect of Improving Aspect Ratio and Electrode Spacing of the Crystalline Silicon Solar Cell

The screen printed technique is one of the electrode forming technologies for crystalline silicon solar cell. It has the advantage that can raise the production efficiency due to simple process. The electrode technology is the core process because the electrode feature is given a substantial factor (for solar cell efficiency). In this paper, we tried to change conditions such as squeegee angle 55∼75°, snap off 0.5∼1.75 mm, printing pressure 0.6∼0.3 MPa and 1.6∼2.0 mm finger spacing. As a result, the screen printing process showed an improved performance with an increased height higher finger height. Optimization of fabrication process has achieved 17.48% efficiency at screen mesh of 1.6 mm finger spacing.

Comparative study of CdTe thin film solar cells with wet and dry CdCl 2 treatment process

In this work, CdTe films were prepared by r.f. magnetron sputtering. Influence of conventional wet and dry CdCl2 treatments on the structural and optical properties of CdTe films were investigated by field emission scanning electron microscope (FE-SEM), x-ray diffraction (XRD), and UV-Visible spectrophotometer. Also, CdS/CdTe thin film solar cells were fabricated by all sputtering process and the cell characteristics were studied. The as-deposited CdTe thin films had a zincblende structure highly oriented with the (111) direction parallel to the substrate surface. The CdTe films lose their preferred orientation and become polycrystalline by heat treatment with dry CdCl2 treatment. The wet CdCl2 treatment exhibited a similar trend, but is less effective for grain growth than dry CdCl2 treatment. The photovoltaic properties of the CdS/CdTe solar cell were considerably improved with the increase in the annealing temperature, which was caused by the increase of grain size in CdTe films. However, the wet CdCl2 process was not suitable for reproducible fabrication.

A Study of Pore Formation of AAO Film on Si Substrate with Optimizing Process

AAO films were fabricated on two kinds of substrates such as and Al/Ni/Ti/Si. To obtain well-aligned AAO film, we optimized process condition for buffer layer, electrolyte and voltage. In the case of oxalic acid, the AAO film with pore size of approximately 45 nm was obtained at voltage of 40 V, temperature of , oxalic acid of 0.3 M and widening time of 60 min. Then the thickness of barrier is less than 600 nm. In the case of sulfuric acid, the AAO film has pore size of 40 nm and barrier thickness of 400 nm with optimum conditions such as voltage of 25 V, temperature of , sulfuric acid of 0.3 M and widening time of 60 min.