I was reading an article on how solar cells work in this website- http://science.howstuffworks.com/environmental/energy/solar-cell2.htm
In that website I have a doubt in the first paragraph i.e.-
"Silicon has some special chemical properties, especially in its crystalline form. An atom of silicon has 14 electrons, arranged in three different shells. The first two shells -- which hold two and eight electrons respectively -- are completely full. The outer shell, however, is only half full with just four electrons. A silicon atom will always look for ways to fill up its last shell, and to do this, it will share electrons with four nearby atoms. It's like each atom holds hands with its neighbors, except that in this case, each atom has four hands joined to four neighbors. That's what forms the crystalline structure, and that structure turns out to be important to this type of PV cell."
In that paragraph there is this line that silicon's outer shell has 4 electrons which is half full so it means that its capacity of holding electrons in the outer shell is 8 electrons but according to the $2n^2$ formula silicon's outer shell should have a capacity of holding 18 electrons but why it is not written like that there in the article??
And if its a misprint and i am correct then the whole working of the PV cell in that article should change so whats the correct working??