The  challenge for Si thin-layers on foreign substrates in PV applications is to produce an active Si layer of sufficient electronic quality, with a thickness on the order of 10 μm, and at a fast deposition rate of about 1 μm/min on a low-cost substrate such as glass. The principal electronic quality requirement is a long minority-carrier diffusion length comparable to the layer thickness, which demands that the grain size be similar.  Unfortunately, efforts around the world have thus far only resulted in partial solutions (e.g., fast epitaxy of high-quality layers on Si substrates, fast deposition of submicron-grain-size layers on high-temperature glass, or slow solid-state crystallization from slowly deposited a-Si layers yielding stressed films).

We had partial success with a gas-phase growth technique that produces continuous Si layers of 5-20-μm thickness with 5-10-μm grain size on high-temperature glass at a growth rate of 1-10 μm/min.  So far, the layer quality is not sufficient, and more work is needed to improve its properties and PV performance.