Protocrystalline Silicon for Micromorph Tandem Cells on Gen. 5 Size

Inventux Technologies AG is a high volume producer of Micromorph (a-Si: H/mu c-Si: H) tandem modules. The light-induced degradation of hydrogenated amorphous silicon (a-Si: H), called Staebler-Wronski effect (SWE), limits the stabilized efficiency of a-Si: H-based solar cells. Several laboratories have reported on the development of a-Si: H with increased resistance against light-soaking. This so-called 'protocrystalline' silicon can be grown with plasma-enhanced chemical vapor deposition (PECVD) by diluting the silane source gas with hydrogen. The aim of the work presented in this paper was to scale-up the laboratory results on protocrystalline silicon to a size of 1.43 m(2) (Gen. 5) using a process that is suitable for high volume production. We demonstrate that the strict boundary conditions regarding uniformity and growth rate, which are necessary for a production process, can be met. The reduced light-induced degradation of protocrystalline solar cells fabricated with the newly developed process is confirmed by a light-soaking experiment. As an outlook towards future work, we discuss issues related to the implementation of a protocrystalline top cell in the Micromorph tandem configuration. The challenge of choosing the right top-cell thickness is illustrated by experimental results on two tandem cells. The top cells of these tandems contain protocrystalline i-layers of different thicknesses.