SUGAR · Silicon sUbstrates from an inteGrated Automated pRocess

Since the silicon wafer still accounts for a substantial part of the cost of solar modules, reducing the silicon consumption per watt peak is one of the most effective ways of reducing the overall cost of PV systems. In this project we propose a methodology to produce a high-efficiency solar module with a very limited amount of Si. The methodology is based on two technologies: the first one for the fabrication of the solar wafers, the second one for the processing of this new material.For the fabrication of the ultra-thin solar wafers, a material, for instance a metallic material, with a high coefficient of thermal expansion, is deposited on the substrate at high temperature. The system is then cooled down, and the difference of thermal expansion induces some stress in the silicon substrate. When the stress exceeds the mechanical strength of silicon, a crack propagates parallel to the surface, and the top layer (which thickness reaches in this case around 50 µm) of silicon is detached from the parent substrate. The thin silicon layer and the metal layer are rolled due to some remaining stress. This stress can be annihilated by dipping the sample in a chemical bath.The processing of this material into a solar module is not trivial and the second technology developed in this project proposes to glue the ultra-thin wafer to a definitive glass superstrate. The Si material is then processed into a solar cell, and encapsulated into a module. The module and the solar cell process are integrated and are performed at low temperature (heterojunction-based interdigitated back contact) to be compatible with the glass thermo-mechanical properties.The project directly addresses a core issue of photovoltaic research and proposes an elegant, low-cost and very innovative solution to solve it.