The current technologies to produce photovoltaic modules exhibit features, which prevent cost-reduction to below 0,5 /Wp: - Sawing/Wafering and Module assembly is costly and material intensive for wafer solar cells. Efficiency is comparatively low for classical thin-film solar cells (CdTe, CIS, a-Si/µc-Si, dye, organic). One approach to avoid both disadvantages is the so-called crystalline Si thin-film lift-off approach, where thin c-Si layers are stripped from a silicon wafer. This approach has the potential to reach > 20% efficient solar cells, however handling issues stop quick progress so far.
The basic idea of the current project is to enable the use of lift-off films in a nearly handling-free approach, to avoid limitations by handling issues. The technological realization has the following key features and steps:
- Continuous separation of a very thin (< 10 µm) c-Si foil from the circumference of a monocrystalline silicon ingot - Attachment to a high-temperature stable substrate of large area (e.g. graphite, Sintered Silicon, or ceramics), which can also serve as module back side.
- High-temperature re-organisation of the silicon foil followed by in-situ epitaxial thickening (~40 µm base thickness) in an in-line chemical vapour deposition reactor, including pn-junction formation
- Processing of high-efficiency solar cells and formation of integrated interconnected high-voltage modules
- Encapsulating into a module (glass / encapsulant only if needed)
The resulting module to be demonstrated in R2M-Si has a cost potential around 0.55 /Wp, at 18% module efficiency and thus low Balance-of-System cost. Future enhanced R2M-Si modules can exceed even 20% efficiency, at costs below 0.5 /Wp. The project shall demonstrate the feasibility of the most critical process steps like continuous layer detachment, bonding to a carrier substrate, high-quality epitaxy, handling-free solar cell processing and module integration. As a deliverable, a mini module of higher than 18% efficiency shall be prepared.
