Kerf-less removal of Si, Ge, and III-V layers by controlled spalling to enable low-cost PV technologies

Kerf-less removal of surface layers of photovoltaic materials including silicon, germanium, and III-Vs is demonstrated by controlled spalling technology. The method is extremely simple, versatile, and applicable to a wide range of substrates. Controlled spalling technology requires a stressor layer, such as Ni, to be deposited on the surface of a brittle material, and the controlled removal of a continuous surface layer could be performed at a predetermined depth by manipulating the thickness and stress of the Ni layer. Because the entire process is at room temperature, this technique can be applied to kerf-free ingot dicing, removal of preformed p-n junctions or epitaxial layers, or even completed devices. We successfully demonstrate kerf-free ingot dicing, as well as the removal of III-V single-junction epitaxial layers from a Ge substrate. Solar cells formed on the spalled and transferred single-junction layers showed similar characteristics to nonspalled (bulk) cells, indicating that the quality of the epitaxial layers is not compromised as a result of spalling.