![]() The sample then was compressed mechanically at a pressure of 279 kg/cm 2. The TiO 2 paste was scraped by the doctor blading method on a transparent fluorine-doped-tin oxide (FTO) glass, which has sheet resistance 8 Ω/□. Spin-Coating Replicationġ0 wt % TiO 2 paste was prepared by mixing nanocrystalline TiO 2 particles (TG–P25, Degussa, Shinjuku, Tokyo, Japan the average nanoparticle diameter was about 25 to 30 nm) with tert-butyl alcohol and deionized water. After that, the pore diameter of the anodic alumina was further widened by immersing the sample in 6 wt % phosphoric acid at 40 ☌ for 12 min. ![]() The last anodization process was processed under the same conditions as the first anodization process, but the anodization period was reduced to 75 s. Then, the anodic alumina layer was removed by wet chemical etching in 6 wt % phosphoric acid (H 3PO 4) with 1.8 wt % chromic acid (H 2CrO 4) at 60 ☌ for 60 min. During the anodization, the solution was stirred by a pump circulation system. In the first anodization process, the pre-treated aluminum sheets were immersed in 0.1 M oxalic acid dihydrate (SIGMA-ALDRICH 99.5%, diluted by DI water) at a constant voltage of 80 V and a temperature of 4 ☌ for 3 h. The AAO template was fabricated by using a two-step anodization process. Super purity aluminum sheets (99.969%, Toyo Aluminium Foil, Osaka, Japan) of 0.25 mm thickness were used as a substrate to serve as the original mold. In this paper, we also developed a two-step process to overcome the issue. The process, however, needs heat treatment over 100 ☌, which is not compatible for the process for fabricating DSSCs. The efficiency increase can be up to 3%–5%. Using PMMA or PDMS as anti-reflection layers on solar cells has been reported with great improvement on light harvest efficiency. Moreover, since the thin PMMA films are flexible, they can be mounted on curved optical structures for many interesting applications. The additional PMMA AR films have gradual variation in the refractive index that can effectively absorb incident light and greatly reduce reflectivity. The additional AR layer was made by polymethyl methacrylate (PMMA) because of its high resolution, low cost and optical transparency in the wavelengths between visible and near-infrared regions. The moth-eye structure was fabricated based on the replication technology of an anodic aluminum oxide (AAO) template. In this paper, we propose a simple and cheap method to fabricate moth-eye structured additional AR layers that combine with dye-sensitized solar cell (DSSC) devices. Therefore, a cheap and efficient technique to fabricate moth-eye structured AR layers is needed for photovoltaic devices. However, these techniques are time consuming and expensive. E-beam lithography, photolithography, and nano-sphere lithography techniques are available for fabricating moth-eye patterns. On the other hand, subwavelength moth-eye structures have been explored in literature for decades, and it has been demonstrated that this structure has a low reflection over a broad spectral range. A similar texturing technique using acid solution has also been applied to multi-crystalline silicon-based solar cells. The idea arises from the gradual variation in the refractive index between air and silicon that reduces the loss of light from reflection. Besides multilayer coating, surface texturization by alkaline etching technique is an alternative method that has been widely used in silicon-based solar cells. However, the process instability, high cost, and high-temperature procedure limit the applications of these AR films. Multilayer AR film also have been developed in order to further reduce the loss. For example, silicon nitride AR coating has been widely used in solar cells since it is easy to fabricate however, its performance is not satisfying due to its narrow-band and narrow-angle properties. The literature has shown that there is still more than 30% of incident sunlight lost, even with adopting antireflection (AR) film in solar devices. Minimizing optical reflection in solar cells to improve conversion efficiency is always a major challenge.
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