Electroforming can be used to separate electrodeposited metal from the surface of a metal or other conductive material to produce new metallic products with fine shapes. Because Si thin-film solar cells possess fewer absorption layers than other compound thin-film solar cells, light-trapping technology is required to increase the rate of light absorption. Various metal substrate shapes can be constructed in the electroforming process, depending on the shape of the mandrel surface. The objective of this study was to construct specific textured substrates through electroforming to improve light-trapping efficiency in silicon (Si) thin-film solar cells. We constructed pyramid-and V-shaped substrates at angles of 30°, 45°, and 60° by electroforming. To observe the reflective properties of the manufactured substrates, we used an ultraviolet/visible (UV/Vis) spectrometer to measure the total and diffused reflectance. We found that an increase in the contact angle due to changing texture led to a decrease in total reflectance in Fe-Ni alloy substrates. We concluded that substrate texture led to an increase in the light paths in the light-absorbing layers of the thin-film solar cells.
Electroplating is a widely used surface treatment method in the manufacturing process of electronic parts and uniformity of the electrodeposition thickness is very crucial for these applications. Since many variables including fluid flow influence the uniformity of the film, it is difficult to conduct efficient research only by experiments. So many studies using simulation have been carried out. However, the most popular simulation technique, which calculates secondary current distribution, has a limitation on the considering the effects of fluid flow on the deposition behavior. And modified method, which is calculating a tertiary current distribution, is limited to a two-dimensional study of simple shapes because of the massive computational load. In the present study, we propose a new electroplating simulation method that can be applied to complex shapes considering the effect of flow. This new model calculates the electroplating process with three steps. First, the thickness of boundary layers on the surface of the cathode plane and velocity magnitudes at the positions are calculated from the simulation of fluid flow. Next, polarization curves of different velocities are obtained by calculations or experiments. Finally, both results are incorporated into the electroplating simulation program as boundary conditions at the cathode plane. The results of the model showed good agreements with the experimental results, and the effects of fluid flow of electrolytes on the uniformity of deposition thickness was quantitatively predicted.
Differences in the thermal expansion of the semi-conductor layer and the substrate of thin film solar cells can lead to thermal deformation of the cell during thermal processing. To control this deformation, the substrate needs to have a thermal expansion behavior similar to that of the semi-conductive layer of the cell. In order to develop such a metal substrate for thin film silicon solar cells, a Fe-42 wt. %Ni alloy with low thermal expansion characteristics was fabricated by electroforming. The thermal expansion behaviors of as-deposited and heat-treated Fe-42 wt. %Ni alloys were measured using a Thermal Mechanical Analyzer. A rapid change in thermal expansion was observed between 350 and 400 C in the as-deposited Fe-42 wt. %Ni alloy. However, when the alloys were heat treated at temperatures higher than 500 C, their thermal expansion behaviors were stable and their thermal expansion coefficients were 4-5 Â 10 À6 / C. Based on such data, Finite Element Analysis was applied to calculate the thermal deformation of the cell that occurs during cooling from a virtual coating process temperature to room temperature, using the Algor program. The analyses showed that the cell on the heat-treated Fe-42 wt. %Ni alloy substrate had less residual stress and a lower amount of deformation compared to that on a commercial stainless steel substrate. V C 2014 AIP Publishing LLC. [http://dx.
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