Weibull strength size effect of diamond wire sawn photovoltaic silicon wafers

Abstract

A good comprehension of the mechanical properties of photovoltaic silicon wafers is crucial to maintain low breakage rates during solar cell manufacturing. As brittle material, silicon wafers are theoretically subject to a strength size effect. This study aims at determining whether this effect should be considered when comparing the strength of photovoltaic wafers. We derive a theoretical strength scaling law and perform an extensive experimental study on 240 diamond-wire sawn silicon wafers, which have the particularity of exhibiting an anisotropy in Weibull parameters. We compare test results from three different bending configurations and show that a size effect is only observable when loading the wafers perpendicular to the saw marks. Strength values obtained when loading the wafers in the direction of the wire yield identical results regardless of the size of the tested area. These findings can open up prospects for the standardization of testing methods for photovoltaic wafers.