Chapter IC-1 - Thin-Film Silicon Solar Cells

Abstract

Amorphous silicon thin films were first deposited by plasma-enhanced chemical vapor deposition (PECVD). The amorphous silicon layers deposited from silane by PECVD could be doped by adding to the plasma discharge either phosphine to form n-type layers, or diborane to form p-type layers. The conductivity of these thin amorphous silicon layers could be increased by several orders of magnitude. Amorphous silicon solar cells at first found only niche applications, especially as the power source for electronic calculators. For 15 years or so, they have been increasingly used for electricity generation: they seem particularly well-suited for wide applications in building-integrated photovoltaics. One of their main advantages is that they are available in the form of monolithically integrated large-area modules. In amorphous silicon thin films, both the bond angles and the bond lengths vary in a random fashion: There is a whole distribution of values. If the amorphous silicon layer has just a low “amount of disorder,” then the distributions for bond angles and bond lengths will be very narrow.