In silicon solar cells (photoelectric conversion apparatuses) and the like, irregularities called a texture are provided in a light-receiving surface of a silicon substrate in order to suppress reflection of incident light and in order for the light taken-in by the silicon substrate not to be leaked to the outside. Generally, texture formation in a surface of the silicon substrate has been performed by a wet process in which an alkali (KOH) aqueous solution is used as an etchant. In the texture formation by the wet process, a washing process using hydrogen fluoride, a heat treatment process, and the like are necessary as a post treatment. Therefore, in this process, the surface of the silicon substrate may be contaminated, and there is a disadvantage in a cost aspect.
Furthermore, the silicon substrate in which the texture may be formed by the wet process is limited to a silicon substrate having substrate surface orientation (100) (refer to PTL 1 and the like), and it is difficult to form a texture in a surface of a silicon substrate having other substrate surface orientations by the wet process.
On the other hand, methods of forming a texture in a surface of a silicon substrate by a dry process have been suggested. For example, 1) a method of using a technology called reactive ion etching by plasma, 2) a method of etching the surface of the silicon substrate by introducing any one kind of gas selected from ClF3, XeF2, BrF3, and BrF5 into a reaction chamber, in which the silicon substrate is placed, under an atmospheric-pressure atmosphere (refer to PTL 2, PTL 3, and PTL 4), and 3) a method of forming irregularities in the surface of the silicon substrate by emitting a laser beam to the silicon substrate under an oxygen-containing atmosphere (refer to PTL 5 and PTL 6) have been suggested.
Furthermore, an attempt for increasing material efficiency of silicon by making a silicon substrate of a solar cell thin has been conducted (refer to PTL 7). Specifically, since the silicon substrate in the related art is obtained by cutting a silicon ingot into a wafer shape, the thickness thereof becomes several hundred micrometers. However, in the solar cell, a thickness necessary for the silicon substrate, which contributes to photoelectric conversion, is 100 μm or less. Accordingly, when the silicon substrate becomes thin, the material efficiency of the silicon increases.
PTL 7 discloses a method in which ions are implanted into a layer which is arranged at a predetermined depth of a silicon substrate, the silicon substrate to which the ions are implanted is heated, and the silicon substrate is cut at the above-described layer to obtain a thin silicon substrate. Similarly, a method of peeling a surface film of a substrate by emitting ion beams to a surface of the silicon ingot substrate has been suggested (refer to PTL 8 and PTL 9).
On the other hand, solar cells are largely classified into a both-surface electrode type solar cell in which an it electrode and a p electrode are disposed on a light-receiving surface and a rear surface thereof, respectively, and a rear-surface type solar cell in which the n electrode and the p electrode are disposed on the rear surface of the light-receiving surface. As one kind of the rear-surface type solar cell, an aspect in which a PN junction provided on the light-receiving surface and an electrode on the rear surface are connected by a through-hole has been disclosed, and this aspect is called “a metal-warp through structure hack contact cell” (for example, refer to PTL 10 and NPL 1).
USPTO Backgrounds
USPTO Backgrounds