Soonwoo Kwon

Effect of Saw-Damage Etching Conditions on Flexural Strength in Si Wafers for Silicon Solar Cells

【We have studied methods to save Si source during the fabrication process of crystalline Si solar cells. One way is to use a thin silicon wafer substrate. As the thickness of the wafers is reduced, mechanical fractures of the substrate increase with the mechanical handling of the thin wafers. It is expected that the mechanical fractures lead to a dropping of yield in the solar cell process. In this study, the mechanical properties of 220-micrometer-solar grade Cz p-type monocrystalline Si wafers were investigated by varying saw-damage etching conditions in order to improve the flexural strength of ultra-thin monocrystalline Si solar cells. Potassium hydroxide (KOH) solution and tetramethyl ammonium hydroxide (TMAH) solution were used as etching solutions. Etching processes were operated with a varying of the ratio of KOH and TMAH solutions in different temperature conditions. After saw-damage etching, wafers were cleaned with a modified RCA cleaning method for ten minutes. Each sample was divided into 42 pieces using an automatic dicing saw machine. The surface morphologies were investigated by scanning electron microscopy and 3D optical microscopy. The thickness distribution was measured by micrometer. The strength distribution was measured with a 4-point-bending tester. As a result, TMAH solution at

The flexural strengths of silicon substrates with various surface morphologies for silicon solar cells

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Aluminum fire-through with different types of the rear passivation layers in crystalline silicon solar cells

showed the best performance for flexural strength.】

Back surface field properties with different surface conditions for crystalline silicon solar cells

The influence of various surface morphologies on the mechanical strength of silicon substrates was investigated in this study. The yield for the solar cell industry is mainly related to the fracturing of silicon wafers during the manufacturing process. The flexural strengths of silicon substrates were influenced by the density of the pyramids as well as by the size and the rounded surface of the pyramids. To characterize and optimize the relevant texturing process in terms of mechanical stability and the fabrication yield, the mechanical properties of textured silicon substrates were investigated to optimize the size and morphology of random pyramids. Several types of silicon substrates were studied, including the planar type, a textured surface with large and small pyramids, and a textured surface with rounded pyramids. The surface morphology and a cross-section of the as-textured and fractured silicon substrates were investigated by scanning electron microscopy.

Constant capacitance technique to study electrical instabilities in InP MIS provided by PECVD silicon nitride

Aluminum penetration during dielectric layer annealing on silicon was studied for solar cell application. The thickness and uniformity of the aluminum-doped region was examined in variously annealed dielectric layers. Three types of silicon wafers were used with (1) bare Si, (2) SiO2 layer (80 nm)/Si, and (3) SiNX layer (80 nm)/Si. Local metal contacts were made through laser-drilled holes, and annealing was tested at four different temperatures. Reactions between aluminum and silicon were observed by cross-sectional scanning electron microscopy. Reactions occurred at 660 °C on bare Si and at ca. 690 °C on the SiO2 layer. However, the SiO2 did not withstand annealing at higher temperatures. The SiNX layer showed no Al-BSF region in samples annealed at up to 760 °C, making it a suitable material for rear passivation layers in local contact Si solar cells. A Si solar cell fabricated by laser drilling and screen printing showed an efficiency of 12.41% without optimization.

Improvement on surface texturing of single crystalline silicon for solar cells by saw-damage etching using an acidic solution

【To reduce manufacturing costs of crystalline silicon solar cells, silicon wafers have become thinner. In relation to this, the properties of the aluminium-back surface field (Al-BSF) are considered an important factor in solar cell performance. Generally, screen-printing and a rapid thermal process (RTP) are utilized together to form the Al-BSF. This study evaluates Al-BSF formation on a (111) textured back surface compared with a (100) flat back surface with variation of ramp up rates from 18 to

Effects of textured morphology on the short circuit current of single crystalline silicon solar cells: Evaluation of alkaline wet-texture processes

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Effect of surface morphology on screen printed solar cells

/s for the RTP annealing conditions. To make different back surface morphologies, one side texturing using a silicon nitride film and double side texturing were carried out. After aluminium screen-printing, Al-BSF formed according to the RTP annealing conditions. A metal etching process in hydrochloric acid solution was carried out to assess the quality of Al-BSF. Saturation currents were calculated by using quasi-steady-state photoconductance. The surface morphologies observed by scanning electron microscopy and a non-contacting optical profiler. Also, sheet resistances and bulk carrier concentration were measured by a 4-point probe and hall measurement system. From the results, a faster ramp up during Al-BSF formation yielded better quality than a slower ramp up process due to temperature uniformity of silicon and the aluminium surface. Also, in the Al-BSF formation process, the (111) textured back surface is significantly affected by the ramp up rates compared with the (100) flat back surface.】

The effect of tertiary-butyl alcohol on the texturing of crystalline silicon solar cells

Abstract The charge trapping behaviour in silicon nitride/InP metal insulator semiconductor (MIS) capacitors is investigated by a constant capacitance technique at room temperature. Silicon nitride films were formed by a conventional plasma enhanced chemical vapor deposition (PECVD) technique where MIS structures were grown simultaneously on n- and p-type InP to observe the effect of electron and hole trapping, respectively. We have found that the carrier trapping by direct tunneling near the silicon nitride/InP interface is dominant under low insulator fields for both n- and p-type samples. The amount of injected charges was similar for both types of MIS prepared under same condition. This behaviour is attributed to the amphoteric nature of silicon dangling bonds. The injection of carriers to the bulk of the silicon nitride assisted by the electric field occurs at high insulator fields. This phenomena is apparent particularly for MIS diodes prepared with a smaller ammonia to silane partial pressure ratio in deposition. It is also confirmed that the trap density near the silicon nitride/InP interface is about one order of magnitude higher than that of the silicon nitride bulk due to the initial transient phenomena of the PECVD process.