Photoelastic characterization on multicrystalline silicon substrates for solar cell

By using a scanning infrared polariscope (SIRP), the absolute difference of refractive index vertical bar Delta n vertical bar and the principal direction psi of strain-induced birefringence have been characterized in a multicrystalline silicon substrate sliced from an ingot grown by conventional casting technique. The vertical bar Delta n vertical bar is concentrated with gradual variation of psi in the shapes of distorted square-pillar and straight needle along and around a part of the grain boundaries. The averaged value of vertical bar Delta n vertical bar is 2.9 x 10(-5) over whole the substrate and the maximum value of vertical bar Delta n vertical bar attains 2 x 10(-4). The vertical bar Delta n vertical bar is also decreased with drastic change of psi in the shapes of straight line and cell-like structure inside the grain, which corresponds plastic deformations caused by crystal defects such as dislocation and/or subgrain. Since the concentration of strain-induced birefringence as well as its local relief by plastic deformations observed here is considerably associated with the mechanical strength of the substrate, we can conclude that the SIRP measurement is useful for practical diagnoses of commercial substrates of multicrystalline silicon for solar cell. (c) 2006 Published by Elsevier Ltd.