Eun-Woo 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.

Dependence of Cu(In,Ga)Se2 Solar Cell Performance on Cd Solution Treatment Conditions

In the current study, chemical bath deposition (CBD) was used to grow CdS thin films on a Cu(In,Ga)Se2 (CIGS) absorption layer, in order to examine the effects of CdS deposition conditions on the properties of CIGS solar cell devices. The dip time leading up to the start of CdS synthesis is thought to be an important process variable determining the concentration of Cd ions diffused into the CIGS as well as the condition of the CIGS surface. Accordingly, the behavior of the CIGS solar cell efficiency variation was observed while different dip times were applied, at 4, 15 and 30 minutes, respectively. When the dip time was extended, the series resistance (Rs) of the device fell by a substantial margin, leading to improved photoelectric conversion efficiency and enhanced uniformity in device properties. This can be attributed to the effect of CIGS surface cleaning by the NH4OH contained in the reaction solution.

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.

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).