A method for preparing silicon substrate having average crystallite size greater than or equal to 20 μm, including at least the steps of: (i) providing polycrystalline silicon substrate of which average grain size is less than or equal to 10 μm; (ii) subjecting substrate to overall homogeneous plastic deformation, at temperature of at least 1000° C.; (iii) subjecting substrate to localized plastic deformation in plurality of areas of substrate, called external stress areas, spacing between two consecutive areas being at least 20 μm, local deformation of substrate being strictly greater than overall deformation carried out in step (ii); step (iii) being able to be carried out subsequent to or simultaneous to step (ii); and (iv) subjecting substrate obtained in step (iii) to recrystallization heat treatment in solid phase, at temperature strictly greater than temperature used in step (ii), in order to obtain desired substrate.