1. Field of Invention
The present invention relates to a solar cell and, more particularly, to a method for making a thin-film poly-crystalline silicon solar cell on an indium tin oxide (“ITO”)-glass substrate at a low temperature.
2. Related Prior Art
Various materials have been used to make solar cells in various processes in various research institutions around the world. For example, there are solar cells based on Si, GaAs, InP, GaInP, CdTe and CuInSe2. The internal quantum efficiencies of the solar cells are different. The silicon solar cells are the most popular among these solar cells in consideration of the internal quantum efficiencies and costs. The silicon solar cells includes single-crystalline, poly-crystalline and amorphous silicon solar cells. The internal quantum efficiencies of the single-crystalline silicon solar cells are about 24.7%, the poly-crystalline silicon solar cells 19.8%, and the amorphous silicon solar cells 14.5%. The internal quantum efficiencies of the single-crystalline and poly-crystalline silicon solar cells are high, but the prices are also high. The prices of the amorphous silicon solar cells are low, but the internal quantum efficiencies are also low. To reduce the costs, there have been devised thin-film poly-crystalline silicon solar cells.
The internal quantum efficiencies of the thin-film poly-crystalline silicon solar cells made in laboratories can be higher than 30%. However, the internal quantum efficiencies of the thin-film poly-crystalline silicon solar cells on the market are lower than 20%. Referring to FIG. 7, a typical thin-film poly-crystalline silicon solar cell includes a laminate 5 including a substrate 51, a conductive film 52 coated on the substrate 51 and a poly-crystalline silicon film 53 coated on the conductive film 52. However, the grains of the laminate 5 cannot reduce the odds of the electrons and holes hitting the crystal boundaries. Because the limited mobility and diffusion length are limited, the internal quantum efficiency of the conventional thin-film silicon solar cell is low.
The present invention is therefore intended to obviate or at least alleviate the problems encountered in prior art.