Fabrication of Crystalline Si Thin Films for Photovoltaics

Abstract

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.

Dynamics of Plasma‐Assisted Epitaxial Silicon Growth Driven by a Hydrogen‐Incorporated Nanostructure for Novel Applications

“…[2,3,15] In the last decade, studies on plasma-epi Si have primarily focused on two aspects: improving the charge-carrier transport properties for electronic applications and suppressing the growth of plasma-epi Si for high-efficiency SHJ solar cells. [2,3,[6][7][8][9][10][11][12][13][14][15][16] Plasma-assisted epitaxially grown silicon (plasma-epi Si) is a new silicon-based material with a tailorable nanostructure. Nanovoids can be introduced into plasma-epi Si during growth, enabling the bottom-up fabrication of porous Si for applications such as batteries, hydrogen storage, and even explosives.…”

“…First, the low growth temperature of plasma‐epi Si restricts the surface mobility of reactive species, resulting in incomplete surface reconstruction and crystallographic defects such as dislocations and stacking faults. [ 16 ] Second, plasma‐epi Si consists of a high concentration of SiH bonds owing to the hydrogen radicals in the plasma. This hydrogen incorporation can also induce defects such as hydrogen‐incorporated nanovoids and platelets.…”

“…[ 2,3,15 ] In the last decade, studies on plasma‐epi Si have primarily focused on two aspects: improving the charge‐carrier transport properties for electronic applications and suppressing the growth of plasma‐epi Si for high‐efficiency SHJ solar cells. [ 2,3,6–16 ]…”