The present disclosure relates to crystalline silicon solar cell manufacturing, and more particularly, to a method for texturing a crystalline silicon substrate utilizing an aqueous alkaline etchant solution which includes a nanoparticle slurry as one of the components thereof.
A photovoltaic device is a device that converts the energy of incident photons to electromotive force (e.m.f.). Typical photovoltaic devices include solar cells, which are configured to convert the energy in the electromagnetic radiation from the Sun to electric energy.
In a typical solar cell, single-crystalline silicon is generally used as one of the components of the cell. In such applications, the single-crystalline silicon needs to have a non-planar surface to improve light capture. Typically, the non-planar surface has concave and convex patterns with a minute pyramid (i.e., square pyramid) shape. In such solar cells, the light reflected from one spot impinges again to another spot on the surface of the crystalline solar cell by virtue of the ‘textured’ surface, penetrating into the solar cell to be effectively absorbed in the solar cell. Although a portion of the impinging light that has not been fully absorbed, but arrives at the back face of the solar cell, is reflected back to the surface again, that portion of impinging light can be reflected again at the surface comprising steeply inclined pyramidal surfaces, thereby confining the light in the solar cell to improve absorption of light and to enhance power generation.
In conventional single-crystalline silicon solar cells, the textured structure is formed by immersing the exposed (100) face of a single-crystalline silicon wafer into an alkaline solution, i.e., sodium hydroxide (NaOH) or potassium hydroxide (KOH), which may also include 5 to 30% by volume of isopropyl alcohol and/or 0.3 to 1.5% by weight of silicon. The silicon is etched into the bath as a bath conditioner.
The etching rate in anisotropic etchants of the kind described above depends on the crystallographic orientation of the silicon surface being etched. The etching rate on the (111) face is significantly lower than the other crystallographic orientations. Accordingly, the (111) face with the slowest etching rate is advantageously left on the surface. Since this (111) face is inclined by about 54 degree against the (100) face, pyramidal projections constituted of the (111) face and its equivalent faces are formed. The pyramid size and density depends on the KOH or NaOH concentration, the amount of silicon already dissolved in the bath, and additive such as isopropyl alcohol.