Dong-Joo Kwak

Fabrication of Titanium-Doped Indium Oxide Films for Dye-Sensitized Solar Cell Application Using Reactive RF Magnetron Sputter Method

To develop high-efficiency transparent conductive oxide glass in a longer wavelength zone for dye-sensitized solar cell (DSC) application, we fabricate titanium-doped indium oxide (ITiO) films on a soda-lime glass substrate by an RF magnetron sputtering. The ITiO films showed a minimum resistivity of 1.25 times 10-3 Omega ldr cm. The transmittance increases from 80% at 450 nm to 90% at 700 nm in the visible spectrum. From the atomic force microscopy result, the surface roughness of the sample showed a change from 10 to 50 nm with annealing temperature. From the XPS result, the concentration ratio (%) for In, Ti, and O was 27 : 2 : 42. The annealing treatment on the ITiO films improves the photovoltaic characteristics of the ITiO-based DSCs, and energy conversion efficiency (eta) is 5.79% (FF: 0.62, Voc: 0.71 V, Jsc: 13.23 mA/cm2) at 100-mW/cm2 light intensity.

Comparison of transparent conductive indium tin oxide, titanium-doped indium oxide, and fluorine-doped tin oxide films for dye-sensitized solar cell application

In this study, we investigate the photovoltaic performance of transparent conductive indium tin oxide (ITO), titanium-doped indium oxide (ITiO), and fluorine-doped tin oxide (FTO) films. ITO and ITiO films are prepared by radio frequency magnetron sputtering on soda-lime glass substrate at 300 °C, and the FTO film used is a commercial product. We measure the X-ray diffraction patterns, AFM micrographs, transmittance, sheet resistances after heat treatment, and transparent conductive characteristics of each film. The value of electrical resistivity and optical transmittance of the ITiO films was 4.15×10 -4 Ω-cm. The near-infrared ray transmittance of ITiO is the highest for wavelengths over 1,000 nm, which can increase dye sensitization compared to ITO and FTO. The photoconversion efficiency (η) of the dye-sensitized solar cell (DSC) sample using ITiO was 5.64%, whereas it was 2.73% and 6.47% for DSC samples with ITO and FTO, respectively, both at 100 mW/cm 2 light intensity.

Texture, Morphology and Photovoltaic Characteristics of Nanoporous F:SnO₂ Films

The nanoporous F:SnO₂ materials have been prepared through the controlled hydrolysis of fluoro(2-methylbutan-2-oxy)di(pentan-2,4-dionato)tin followed by thermal treatment at 400-550℃. The main IR features include resonances at 660, 620 and 540 ㎝-1. From the TG-DTG result, three main mass losses of 6.5, 13.3 and 3.8 at 81, 289 and 490℃ are observed between 50 and 650℃ yielding a final residue of 76.0%. The size of Sn O2 nanoparticles rose from 5 ㎚ to 10-12 ㎚ as the temperature of thermal treatment is increased from 400 to 550℃.

Improved interface properties of yttrium oxide buffer layer on silicon substrate for ferroelectric random access memory applications

Abstract In this paper, we report upon an investigation into the feasibility of Y 2 O 3 films as buffer layers for metal ferroelectric insulator semiconductor type capacitors. Buffer layers were prepared by a two-step process of low temperature film growth using the RF reactive magnetron sputtering method and subsequent rapid thermal annealing. By applying an yttrium metal seed layer of 4 nm, unwanted SiO 2 layer generation was successfully suppressed at the interface between the buffer layer and the Si substrate. Increasing the post-annealing temperature above 700 °C reduced the surface roughness of the Y 2 O 3 films, and increasing the O 2 partial pressure from 10 to 20% increased the surface roughness from 4.0 to 15.1 nm. The Y 2 O 3 films, prepared using an O 2 partial pressure of 20% and annealed at 900 °C, exhibited the best surface roughness characteristics of the samples studied. For a substrate temperature above 400 °C and an O 2 partial pressure of 20%, we observed that a cubic Y 2 O 3 phase dominated the X-ray diffraction spectra. The lowest lattice mismatch achieved between the Y 2 O 3 film and the Si substrate was 1.75%. By using a two-step process, we reduced the leakage current density of Y 2 O 3 films by two orders of magnitude and the D it to as low as 8.72×10 10 cm −2 eV −1 . A Y 2 O 3 buffer layer grown at 400 °C in a 20% O 2 partial pressure and rapidly annealed at 900 °C in an oxygen enviroment exhibited the best overall properties for a single transistor ferroelectric random access memory.

Synthesis of TCO-free Dye-sensitized Solar Cells with Nanoporous Ti Electrodes Using RF Magnetron Sputtering Technology

A new type of dye-sensitized solar cell (DSC) based on a porous type Ti electrode without using a transparent conductive oxide (TCO) layer is fabricated for low-cost high-efficient solar cell application. The TCO-free DSC is composed of a glass substrate/dye-sensitized TiO₂ nanoparticle/porous Ti layer/electrolyte/Pt sputtered counter electrode. The porous Ti electrode (∼350 ㎚ thickness) with high conductivity can collect electrons from the TiO₂ layer and allows the ionic diffusion of I?/I₃?through the hole. The vacuum annealing treatment is important with respect to the interfacial necking between the metal Ti and porous TiO₂ layer. The efficiency of the prepared TCO-free DSC sample is about 3.5% (ff: 0.48, V oc : 0.64V, J sc : 11.14 ㎃/㎠).

The Effects of RF Sputtering Power and Gas Pressure on Structural and Electrical Properties of ITiO Thin Film

Transparent conductive titanium-doped indium oxide (ITiO) films were deposited on corning glass substrates by RF magnetron sputtering method. The effects of RF sputtering power and Ar gas pressure on the structural and electrical properties of the films were investigated experimentally, using a 2.5 wt% TiO2-doped In2O3 target. The deposition rate was in the range of around  nm/min under the experimental conditions of  mTorr of gas pressure and  W of RF power. The lowest volume resistivity of -cm and the average optical transmittance of 75% were obtained for the ITiO film, prepared at RF power of 300 W and Ar gas pressure of 15 mTorr. This volume resistivity of -cm is low enough as a transparent conducting layer in various electrooptical devices, and it is comparable with that of ITO or ZnO:Al conducting layer.

Fabrication and Characterization of Dye-Sensitized Solar Cell Using TiO2-Nanotube Particles by Anodic Oxidation

Anodic oxidation of Ti metal was performed in an ethylene glycol electrolyte with small addition of H2O and NH4F at 60 V. Ti metal plate with a thickness of 100 µm was completely converted into ~200 µm thick membrane of highly ordered TiO2 nanotube (NT) arrays. TiO2 NT arrays are grown in vertical direction to both faces of the Ti-plate. As-fabricated NT membrane is mechanically grinded to yield fine individual NT particles for the photoanode application to dye-sensitized solar cells (DSCs) in replacement of conventional TiO2 particles. Photoconversion efficiency of the DSC using crystalline NT particles is ~7.0%. It can be further improved by controlling TiO2 NT particle dimensions to increase dye attachment, and electron lifetime and mobility due to high surface to volume ratio and less defect density.

Titanium-doped indium oxide films prepared by RF magnetron sputtering

Transparent conductive titanium-doped indium oxide (ITiO) films were prepared on soda-lime glass substrate using an RF magnetron sputter source. The electrical and optical properties of the transparent conductive ITiO film and the photovoltaic performance of the prepared DSCs were examined. The ITiO thin films containing 5 wt.% Ti showed the minimum resistivity of rho = 5.25times10-3 Omega-cm. The optical transmittance increases from 70% at 450 nm to 80% at 700 nm in visible spectrum. In addition, XPS and AFM measurements were performed to investigate the surface structural properties of the films. Finally, the ITiO film used for TCO layer of dye-sensitized solar cells (DSCs) exhibited an energy conversion efficiency of about 3.73% at light intensity of 100 mW/cm2. It can be therefore seen that the ITiO films obtained by RF magnetron sputter system exhibited good transparent conductive properties, well suited for DSCs application.

Improvement of Charge Transfer Efficiency of Dye-sensitized Solar Cells by Blocking Layer Coatings

A layer of thin film less than ~200nm in thickness, as a blocking layer, was deposited by 13.56 MHz radio frequency magnetron sputtering method directly onto the anode electrode to be isolated from the electrolyte in dye-sensitized solar cells (DSCs). This is to prevent the electrons from back-transferring from the electrode to the electrolyte (). The presented DSCs were fabricated with working electrode of F:(FTO) glass coated with blocking layer, dye-attached nanoporous layer, gel electrolyte and counter electrode of Pt-deposited FTO glass. The effects of blocking layer were studied with respect to impedance and conversion efficiency of the cells. The, electrochemical impedances of DSCs using this electrode were : 13.9, : 15.0, : 10.9 and : . The impedance related by electron movement from nanoporous to TCO showed lower than that of normal DSCs. The photo-conversion efficiency of prepared DSCs was 5.97% (: 0.75V, : 10.5 mA/, ff: 0.75) and approximately 1% higher than general DSCs sample.

Electrical Conduction Mechanism of AZO Thin Film and Photo-Electric Conversion Efficiency of Film-Typed Dye Sensitized Solar Cell

In this paper, AZO thin film was deposited on polyethylene terephthalate(PET) substrate by r. f. magnetron sputtering method from a ZnO target mixed with 2[wt%] Al2O3. The flexible film-typed dye sensitized solar cell(F-DSC) was fabricated and photo-electric conversion efficiency was investigated. The results showed that the minimum resistivity and the maximum deposition rate of AZO conducting film were recorded as and 25.5[nm/min], respectively at r.f. power of 220[W]. From the analysis of XPS data an improvement of electrical resistivity or an increase in carrier concentration with increasing sputtering power may be related to the generation of lattice imperfections as a result of increasing component ratio of O1s/Zn2p, which generates donor carriers or active growth of crystalline grain. The photo-electric conversion efficiency of F-DSC with AZO conducting electrode was over 2.79[%], which was comparable as that with commercially available ITO electrode.