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What causes the transformation of a solar cell is the behavior difference of thermal expansion occurred between the substrate and the layer of semiconductor used in the solar cell. Therefore, the substrate has to possess a behavior of thermal expansion that is similar with that of semiconductor layer. This study employed electroforming to manufacture Fe-Ni alloy materials of different compositions. To verify the result from a finite element analysis, a two-dimensional Mo substrate was calculated and its verification experiment was conducted. The absolute values from the finite element analysis of Mo/substrate structure and its verification experiment showed a difference. However, the size of residual stress of individual substrate compositions had a similar tendency. Two-dimensional CIGS/Mo/SiO2/substrate was modeled. Looking into the residual stress of CIGS layer occurred while the temperature declined from 550 o C to room temperature, the smallest residual stress was found with the use of Fe-52 wt%Ni substrate material.

3D ICs involve interconnected ICs as they contact each other by means of through-silicon-vias (TSVs). Although it is a cheap process and suitable to mass production, the conventional sputtering method has not been widely used to fabricate high aspect ratio vias due to its more or less rectilinear propagation property. In this study, the effect of sputtering conditions on the growth mechanism of seed layers was investigated to fabricate 10∶1 or higher aspect ratio TSVs through the conventional sputtering method. In order to improve the quality of Cu seed layers, a Mo buffer layer was pre-deposited because Mo has a good conductivity and an intermediate thermal expansion coefficient between Si and Cu. To obtain a homogeneous and continuous Cu/Mo layers on TSV, the effect of sputtering conditions and substrate tilting was examined. Cu/Mo seed layers with low electrical resistivity of 2.07 microohm centimeters were obtained when the sputtering target power was maintained 5 kW, 0.67 Pa, and with 500W bias. The film stress was tensile in the sputter pressure of 0.67 Pa but close to compressive in the 0.13 Pa conditions.

The effect of bath condition on Ni–Fe alloy coating was investigated. The composition of Ni–Fe alloys was highly dependent on the concentration of iron ions rather than nickel ions. Duty cycle and pH did not show an impact on the composition of Ni–Fe alloys, however the composition of alloys was highly dependent on the current density. When the temperature of the bath was over 45 °C, the composition of nickel was increased, since the limiting current density of nickel was increased. The optimum concentration of bath and operating concentration for the invar Ni–Fe alloy was obtained.

Thermal expansion behavior of Al, Ti, Mo, stainless steel and Fe–Ni alloy foils, which could be used for the substrate of flexible solar cells, were studied experimentally using thermomechanical analyzer (TMA). Electroformed Fe–Ni alloy foils and commercially available 50 μm thick Al, Ti, Mo and stainless steel were used for experiment. The thermal stresses and the displacement of solar cell systems consisted of metal foil substrate and virtual CIS top cell were numerically analyzed. Then measured coefficient of thermal expansion of metal foils and reference thermal expansion coefficient of CIS were used to compute the thermal stresses and the displacement of the thin film layers and the substrates of solar cell systems.

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 × 10−6/ °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.