Strength of Silicon Single-Crystal Wafers for Solar Cells

We consider methods for measuring strength characteristics of brittle materials under axisymmetric bending, for example, of a silicon single crystal obtained by crystallization from melt by the Czochralski method. This material in the form of thin (80-200 mu m) wafers is used in most high-efficiency solar cells with efficiency exceeding 20%. We analyze experimental and theoretical methods for determining stresses. The results of numerical calculation of stresses are compared with experimental data obtained from measuring the interplanar distance in the silicon crystal lattice under loading. It is shown that the familiar formulas calculating stresses and deflection in the theory of elasticity are valid only for loads much smaller than the breaking load. We obtain the load-deflection dependences under the loading ring in axisymmetric bending of thin silicon wafers of different sizes in different experimental geometries and determined their strength depending on the type of finishing of the surface, which substantially affects its strength.