Sang-Hwan Lee

Electrical and Optical Properties of Cadmium Stannate Deposited by RF Magnetron Sputtering

CTO (Cadmium Stannate) thin films, one of TCOs (Transparent Conducting Oxide) having a potential application for photovoltaic or display product, were prepared by using rf magnetron sputtering system. The lowest resistivity of CTO thin film deposited at room temperature was 6.6 × 10−4 ohm · cm with carrier mobility of 9.1 cm2/Vs and carrier concentration of 10.4 × 1020 cm−3. The average transmittance of CTO thin film was found to be over 80% regardless of deposition condition. The transmittance of the annealed CTO thin film at 600°C in air atmosphere, was found to increase upto more than 90%, but the film resistivity degraded by two order of magnitude due to the decreased carrier concentration with minor increase of carrier mobility.

Property of Cu(In,Ga)Se2 Absorption Layer Produced using a Proximity Selenization Method

Cu(In,Ga)Se2 thin films were prepared using co-sputtering and proximity selenization. This new method supplies Se by closely attaching opposite a metal precursor. CuInSe2 thin film was produced at 280°C, and consisted of small structures. As the temperature was increased, more Ga was substituted in place of In, while the X-ray peak of the CuInSe2 shifted to the right. A thin film with a Cu:In:Ga:Se ratio of 1:0.7:0.3:2 was obtained at 480°C, which is comparatively lower than the temperature needed when using Se vapor. This grew into crystals with a diameter of 3–5 μm.

Selenization of Cu-In-Ga Metal Precursor Using DESe(Diethyl Selenide)

In this study, Cu(In,Ga)Se2 thin films were prepared using a Cu-In-Ga metallic precursor and diethylselenide (DESe) vapor. The Cu/(In+Ga) ratio of the precursor was adjusted by modulating the power impressed on the CuGa target. The Cu/(In+Ga) ratio was varied from 0.45 to 1.02, and the prepared precursors were selenized in a 500°C quartz furnace using DESe. The results showed that the preferred crystal phase and the uniformity of the thin film differed according to the composition of the precursor. After selenization, changes in grain size stemming from Cu composition were observed, and the occurrence of a binary phase was verified through KCN etching. Shifts in the Cu11(InGa)9 peak and the separation of CIS and CGS peaks relative to increased Ga content were also observed.

Properties of Cu(In,Ga)Se2 Thin Film by Co-Evaporation

Cu(In,Ga)Se2 (CIGS) compound, which has high optical absorption coefficient as direct transition type semiconductor, is very suitable for thin film solar cell due to its high thermal stability and moisture tolerance as well as its low fabrication cost compared to the standard crystalline Si solar cell. In this research, it was tried to control the absorption capability of CIGS layer by changing Ga/(In + Ga) ratio. The composition of film was changed by controlling the effusion-cell temperature of Cu, In, Ga at a fixed Se flux. Each sample was analyzed by using SEM (scanning electron microscope), EDS (energy dispersive spectroscopy), XRD (X-ray diffractometer) to confirm the optimum composition ratio of Cu/(In + Ga) = 0.82∼0.95, Ga/(In + Ga) = 0.26∼0.31, Cu/Se = 0.5.

Characteristics of CuInSe2 Superstrate Thin Film Solar Cell with Various Back Electrodes

The maximum efficiency of Cu(Inx,Ga1-x)Se2(CIS) superstrate thin film solar cell is smaller than that of CIS substrate thin film solar cell, but its device fabrication price is lower because the number of thin-film process is fewer. In addition, CIS absorber layer is fabricated through binary process to reduce the process temperature and processing price. In this study, CIS superstrate thin film solar cell was fabricated to reduce the device fabrication cost and CIS absorber layer was deposited by the binary process. By using Sodalime Glass (SLG), Al:ZnO and ITO were deposited on n-type transparent electrode layer in the upper part. CIS absorber was individually deposited by InSe(In2Se3) and CuSe in a binary type by using Molecular Beam Epitaxy (MBE). The deposited sample went through heat process, and then electrode was created to fabricate the device. In order to identify the structural and electrical characteristics of the various transparent electrodes, CIS absorber and CIS solar cell device, analysis was conducted by using X-ray Diffractometer(XRD, Bulk, PANalytical), Field Emission Scanning Electron Microscope (FE-SEM, S-4800, HITACHI), Inductively Coupled Plasma (ICP, ICPS-8100, Shimadzu), Secondary Ion Mass Spectrometry (SIMS, IMS 6F, CAMECA) and solar-simulator (AM1.5 g, 100 mW/cm2).

Vertical Growth and Morphology Control of Zinc Oxide Micro Rod

It was tried to fabricate a template substrate having a 3-dimensional structure with micrometer- size diameter in order to extend the p-n junction area of the compound thin film solar cell. The ZnO micro rod layer, which was grown vertically by using the chemical bath deposition, was successfully fabricated as a hexagonal shape along the c-axis which is the preferred growth orientation. The growth of ZnO rod being adequate for device applications was examined through investigating growth mechanism of ZnO rod and optimizing the photo resist profile so as to remove the undercut which was found in the grown ZnO rod. The growth model and material properties of the 3-dimensional ZnO rod were analyzed through the scanning electron microscope.

The Effect of Post-Deposited Na on Cu(Inx,Ga1-x)Se2 Solar Cells by using the Na2S Solution

It is known that even mixing only a small amount of Na has effect on electrical and structural property of the CIGS absorber layer and, as a result, device efficiency is improved. In this study, unlike the conventional method where Na diffuses from SLG while CIGS absorber is growing, a new method was applied. In the new method, Na precursor is deposited on the CIGS absorber layer grown on Al2O3/SLG to incorporate Na. The effect of Na on the absorber layer was observed using secondary ion meass spectroscopy, Hall measurement system, scanning electron microscopy, and x-ray diffraction. As a result, it was found that, in the post deposition treated CIGS absorber layer, Na has effect mostly on the electrical property of CIGS without significant change of the microstructure.

Electrical and Optical Properties of Cd2SnO4 Thin Film Depending on its Chemical Bond

Cd2SnO4(CTO) thin film was made using RF magnetron sputtering and a single (CTO) target. Among various deposition variables, the effect of changes in plasma power on the electrical and optical properties of the film was investigated. It was observed, as plasma power grows, specific resistivity of the thin film increases while transmittance considerably decreases. It was found that such a phenomenon occurred because of the density of the thin film reduced by increased deposition speed. Another noteworthy result obtained through the X-ray photoelectron spectroscopy analysis is that Sn has metallic bond in the case of the thin film deposited under high power. It seems that existence of such metal was another cause of the reduced transmittance of the thin film.

A study of the structure and electrical properties of CuInSe 2 /Cu-substrate

In this study, we have formed form CuInSe2 thin film, using Cu substrate. To form thin film, we deposited on Cu substrate by evaporation and completed the element in 4 steps in total. Notably, our primary focus was on the results of deposition of In on Cu substrate, heat treatment step at low temperature for binary formation by Cu diffusion and at high temperature to convert binary phase to CuInSe2 in the end. With such results from the experiment, we are analyzed the formation of CuInSe2 thin film and the microstructure and electrical properties of the thin film. We are also tried conventional CuInSe2 thin film deposition method relying on co-evaporation and traced the cause of non-formation of CuInSe2 thin film in co-evaporation conditions. The experimental results in this study will make significant contribution to the development of various research techniques concerning flexible solar cell manufacturing processes subsequently.

Properties of Cu(In,Ga)Se2 Thin Film Solar Cells on Ga Temperature Variation

In this paper the effect the Ga/(In+Ga) ratio, which was controlled by Ga cell temperature, on the growth behavior of Cu(In,Ga)Se2 (CIGS) thin film and its photovoltaic performance is presented. It was found that both the grain size and the void density of CIGS layer decreased due to higher incorporation of Ga in CIGS by increasing Ga temperature. It was revealed that the CIGS films satisfying the composition ratio of Ga/(In+Ga) = 0.3∼0.4 and Cu/(In+Ga) = 0.84∼1.04, which were obtained at the Ga temperature of 1033∼1035°C, has the comparable diffraction intensity of (112) and (220) peaks. The (112)/(220) peak ratio of either Cu-rich or heavily Cu-poor CIGS films was found to deviate from unity and the solar cells made at these composition range showed lower photovoltaic performances. The highest efficiency of solar cell obtained by adjusting Ga cell temperature was 8.93% on device area of 0.16 cm2 (fill factor, open circuit voltage, and short circuit current were 50.34%, 576 mV and 30.79 mA/cm2, respectively).