HIGH-EF · Large grained, low stress multi-crystalline silicon thin film solar cells on glass by a novel combined diode laser and solid phase crystallization process

HIGH-EF will provide the silicon thin film photovoltaic (PV) industry with a unique process allowing for high solar cell efficiencies (potential for >10%) by large, low defective grains and low stress levels in the material at competitive production costs. This process is based on a combination of melt-mediated crystallization of an amorphous silicon (a-Si) seed layer (<500 nm thickness) and epitaxial thickening (to >2 µm) of the seed layer by a solid phase crystallization (SPC) process. Melting the a-Si layer and solidifying large grains (about 100 µm) will be obtained by scanning a beam of a diode laser array. Epitaxial thickening of the large grained seed layer (including a pn-junction) is realized by deposition of doped a-Si atop the seed layer and a subsequent SPC process by way of a furnace anneal. Such a combined laser-SPC process represents a major break-through in silicon thin film photovoltaics on glass as it will substantially enhance the grain size and reduce the defect density and stress levels of multi-crystalline thin layers on glass compared e.g. to standard SPC processes on glass, which provide grains less than 10 µm in diameter with a high density of internal extended defects, which all hamper good solar cell efficiencies. It is, however, essential for the industrial laser-SPC implementation that such a process will not be more expensive than the established pure SPC process. A low cost laser processing will be developed in HIGH-EF using highly efficient laser diodes, combined to form a line focus that allows the crystallization of an entire module (e.g. 1.4 m x 1 m in the production line or 30 cm x 39 cm in the research line) within a single scan. Specific attention has been given to identify each competence needed for the success of the project and to identify the relevant partners forming a balanced, multi-disciplinary consortium gathering 7 organizations from 4 different member states with 1 associated country.