Sliver Solar Cell Technology: Pushing the Material Boundaries
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Sliver Solar Cell Technology: Pushing the Material Boundaries Evan Franklin, Andrew Blakers, Klaus Weber, Vernie Everett The Australian National University, Canberra, ACT 0200 Australia. ABSTRACT One of the primary objectives of the global photovoltaic research community is to effect significant manufacturing cost reductions, either by reducing material and processing costs or by increasing solar cell efficiency. One very promising technology for achieving both of these goals is Sliver technology, which offers potential for a 10- to 20-fold reduction in the consumption of purified silicon, while at the same time achieving very high cell efficiencies by fully exploiting the advantages of mono-crystalline silicon. Sliver solar cells are thin, mono-crystalline silicon solar cells fabricated using a combination of micro-machining techniques and standard silicon device fabrication technologies. Rather than fabricating a single solar cell on the surface of a wafer, many hundreds to several thousand individual Sliver solar cells are fabricated within a single wafer. The dimensions of a Sliver cell depend upon wafer size, wafer thickness, and the micro-machining method employed. Cells typically have a length of 5 – 12cm, a width of 0.5 – 2mm, and a thickness of 20 – 60 micron. 20% efficient Sliver solar cells using standard cell processing methods and a robust processing sequence, have been fabricated at ANU. Current research efforts are directed towards developing and establishing new fabrication techniques to further simplify the fabrication sequence and to improve cell efficiency. This paper presents an overview of Sliver technology. The fabrication method and some key challenges in producing Sliver cells is presented along with the measured performance of cells fabricated in the ANU solar research laboratory. INTRODUCTION The global photovoltaic market has grown at well over 40% per annum over the past decade, with estimated production of 27.2 GW [1] and a reported installed capacity of 18.2 GW [2] in 2010. During this period of growth, the manufacturing base has expanded from a relatively small number of players, typically linked to existing large corporations with a wide variety of interests (BP, Shell and Sharp for example), to a number of large and specialized photovoltaic manufacturers with interest across many parts of the entire solar cell value chain, from silicon feedstock to solar system sales (REC, Trina and Suntech for example). The rapid growth within the industry, coupled with continual advances in solar cell technology, has gone hand-in-hand with a decline in costs, as demonstrated by the often cited photovoltaic ‘learning curve’, a recent update of which shows a long-term trend learning rate of around 20% [3]. It remains to be seen, as the industry continues to grow and mature, how far and how fast costs will keep declining. One thing however is clear: there is the ongoing need to find cost reductions through manufacturing scale and efficiency, and through advances in technology. The standard solar cell
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