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 89˚C/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.

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 90˚C showed the best performance for flexural strength.

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.

The subacute toxicity of xylooligosaccharide (XO) was evaluated in SD rats. Groups of 60 male and 60 female rats were orally administered with 0, 333, 1000 or 3000 mg/kg of XO for 13 weeks. The changes of body weight, food and water consumption were investigated for 17 weeks, while heamatological values and histopathological findings were investigated at the end of the 13 weeks and 17 weeks including 4 weeks of recovery periods. No death and toxic effects were observed during the test periods. There were statistically significant changes in several parameters, but these change had no direct relationship to dosage. Clinical changes were general occurrence and no specific toxicity was related to XO. Gross necropsy and histopathology revealed that no target organs were found in the treated mouse with XO. According to the results, no-observed effect level of XO is estimated to be above 3000 mg/kg.

To evaluate the bacterial reverse mutation of xylooligosaccharide(XO)s the in vitro Ames test using Salmonella typhimurium (TA98, TA100, TA1535, TA1537) and Escherichia coli (WP2 uvrA) was performed. XO was negative in Ames test with Salmonella typhimurium and Escherichia coli with and without rat liver microsomal enzyme (S-9 fraction). According to the results, XO does not cause bacterial reverse mutation.

The acute toxicity of xylooligosaccharide(XO) was evaluated in SD rats. Groups of 15 male and 15 female rats were orally administered XO (0, 5000 or 10000 ㎎/㎏). The changes of body weight and clinical signs were investigated for 14 days after treatments. No death and toxic effects were observed for 14 days. Soft stool and diarrhea appeared right after treatment for over dose and non-digestive feature of XO but these clinical signs disappeared on the next day. No significant changes in body weight and abnormal gross findings were observed in relation to XO. According to the results, XO has no special toxic effects and LD50 values of XO are above 10000 ㎎/㎏ in male and female rats.