Quasi-monocrystalline silicon wafers have appeared as a critical innovation in the PV industry, joining the most favorable characteristics of the conventional substrates: the higher solar cell efficiencies of monocrystalline Czochralski-Si (Cz-Si) wafers and the lower cost and the full square-shape of the multicrystalline ones. However, the quasi-monocrystalline ingot growth can lead to a different defect structure than the typical Cz-Si process. Thus, the properties of the brand new quasimonocrystalline wafers, based on low and high crystal defect densities, have been for the first time studied from a mechanical point of view, comparing their strength with that of both Cz-Si monocrystalline and typical multicrystalline materials. The study has been carried out employing the four line bending test and simulating them by means of FE models. For the analysis, failure stresses were fitted to a three-parameter Weibull distribution. High mechanical strength was found in all the cases. However, the quasi-monocrystalline wafers characterized by large density of bulk defects, due to the noticeable density of extended defects, showed lower fracture tensions.
-Drilling process on wafers to produce EWT or MWT solar cells is a critical fabrication step, which affects on their mechanical stability. The amount of damage introduced during drilling process depends on the density of holes, their size and the chemical process applied afterwards. To quantify the relation between size of the holes and reduction of mechanical strength, several sets of wafers have been prepared, with different hole diameter. The mechanical strength of these sets has been measured by the ring on ring bending test, and the stress state in the moment of failure has been deduced by FE simulation.
Commercial laminated glass is usually composed of two glass layers and an interlayer of PVB. The viscoelastic behaviour of the PVB layer has to be taken into account when dealing with dynamic loads. This paper shows different Finite Element (FE) models developed to characterize laminated glass. Results are contrasted with data from different reference test cases. First, a quasi-static test is reproduced with a 2d model through a transient analysis. In addition, flexural modes of vibration in a free-free test configuration have been analysed using 2d as well as 3d FE models. Apart from using transient analysis in order to simulate the dynamic behaviour of laminated glass, an iterative procedure has been employed which permits to identify the correct value of the shear modulus of the PVB layer for each mode in an eigenvalue analysis.
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