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 effi
cient 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 chang
es in the morphology and structure of b-Si. As a result, after thermal and chemical treat
ments, the optical characteristics of the b-Si are retrogressed.  
A new fabrication sequence of b-Si solar cells has been proposed and tested, accord
ing 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.