instead of crystalline silicon to produce solar cells. The production cost for amorphous (like glass) silicon is much lower than semiconductor grade crystalline silicon, but the efficiency is considerably lower. According to this article, 3 companies were gearing up in 1997 to produce amorphous silicon solar cells.

In addition to the lower efficiency (on the order of 8% conversion rate), amorphous silicon apparently had some problems with degradation. The previous article mentioned that proper selection of materials makes the degradation manageable. I'm not certain about the current status of the projects. Here's some more info from Down Under.