THICKNESS REDUCTION OF LARGE SIZE HIGH EFFICIENCY SCREEN-PRINTED MULTICRYSTALLINESILICON SOLAR CELLS – POSSIBILITIES AND LIMITATIONS FOR INDUSTRIAL PRODUCTION

摘要

Important efforts have been centred on the modelling of crystallization conditions and the study of thedefects formed during non-optimised growth conditions. This study improved the understanding of the phenomenacausing the formation of internal inclusions and constraints, “grit structure”, and has resulted in a reduction of thenumber of crystallographic defects in the multicrystalline silicon ingots. These improvements enabled the cutting ofthin and large size wafers.A significant part of the subsequent work concerned the development of the thin wafer sawing process andthe study of the origin of mechanical defects coming from thin wafer cutting (150μm for 125mmx125mm dimensionwafers). The wire sawing of 150μm thick wafers was carried out successfully and has showed a potential 30%productivity increase.As the wafer thickness is decreased, it becomes more and more necessary to passivate the cell surface inorder to limit the recombination of the minority carriers. A new cell structure has been used, combining local BSFformed by aluminium deposition and a SiNx:H layer for hydrogen bulk passivation.An encapsulated cell efficiency of 15.3% has been demonstrated on a limited scale production of 150μmthick and of 125mm x 125mm multi-crystalline silicon cells. The mechanical yield of different production steps hasbeen evaluated and compared to the standard thickness cell process. The technological difficulties encountered forkeeping an acceptable mechanical yield in the critical production steps have been analysed. These results showed thepossibilities and the limitations of thin multicrystalline silicon solar cells fabrication.