Fabrication of Crystalline Si Thin Films for Photovoltaics

Crystalline Si (c-Si) thin films have been widely studied for their application to solar cells and flexible electronics. However, their application at large scale is limited by their fabrication process. As reviewed in this paper, many approaches have been studied, but only some of them have been made into large-scale industrial production. The standard wire sawing of Si ingots cannot be scaled down to produce thin c-Si wafers and films due to the brittle nature of c-Si material, the resulting significant thickness variations, and the waste of material. Therefore, techniques based on the kerf-less processes including “top-down” and “bottom-up” approaches have been developed in recent decades. In this review, photovoltaic applications of thin c-Si wafers with thicknesses ranging from 50 μm down to 1 μm are presented first. Then, methods to fabricate c-Si thin films based on both approaches are detailed, including slim-cut, “smart-cut,” epi-free, as well as various growth processes such as molecular beam epitaxy, liquid phase epitaxy, ion beam, and chemical vapor deposition processes at a wide range of growth temperatures, from 1000 °C down to 150 °C. The advantages and disadvantages of these methods are presented and compared.