FABRICATING AND TESTING BLACK SILICON SOLAR CELLS

Abstract

Black Si (b-Si) is a needle-like surface of crystalline Si. The optical radiation incident on it is almost completely absorbed due to multi-reflections from the side surfaces of the needles, which makes b-Si attractive for solar cell applications as antireflection surfaces. Currently, b-Si solar cells are fabricated based on the sequences used for traditional (pyramidal textured) solar cells, namely first, an antireflection surface is formed, and then high-temperature treatments such as oxidation and diffusion are carried out. However, in this case, due to large surface area, the diffusion of dopants within b-Si is much more efficient than in a planar, without texture, wafer. It leads to high doping concentrations and non-uniformity in the dopant. In addition, during the diffusion process, a surface layer of glass is grown, and subsequently removed by wet etching, which leads to noticeable changes in the morphology and structure of b-Si. As a result, after thermal and chemical treatments, the optical characteristics of the b-Si are retrogressed. A new fabrication sequence of b-Si solar cells has been proposed and tested, according to which, the b-Si with preferable height of needles is formed after the main chemical and thermal treatments of the technological process. It has been shown that all performance parameters (open-circuit voltage, short current, fill factor and conversion efficiency) of the new b-Si solar cells are higher than those of the conventional solar cells. Joint use of b-Si and pyramidal textured surfaces can get a more tangible effect.