Crystalline silicon technology for photovoltaics

This paper reviews the CZ and FZ processes of growth of single crystal silicon ingots, the important directional solidification, including casting, techniques of growth of multicrystalline silicon ingots and crystalline silicon ribbon or sheet processes for obtaining wafers for fabrication of large area terrestrial solar cells, It also discusses the advancements which have brought about improvements in solar cell design and processing and have yielded small area laboratory cells of AM 1.5 efficiency, similar to 24% under normal sunlight and similar to 28% under concentrated sunlight, Of these, some advanced structures have been adopted for silicon space cells because of improved power to weight ratio and radiation resistance of these structures, However, the PV industry has so far refrained from adopting the more sophisticated high efficiency solar cell structures, e.g., laser grooved buried contact structure, for commercial terrestrial silicon solar cells as they lower the throughput of solar cell production and do not seem to offer, at this stage, any cost per watt benefit despite giving higher efficiency, Thus, there still remains a need and the challenge to develop a solar cell structure for silicon commercial cells which would yield cells of 16-18% or higher production level efficiencies using a low cost and high throughput process that would help achieve the cost goal of US $ 2 per watt on module level.