Polycrystalline silicon thin‐film solar cells: The future for photovoltaics?

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Abstract
Based on performance, material availability, consumer acceptance, life expectancy, environmental considerations and the potential for low cost, thin‐film polycrystalline silicon solar cells are well placed to have a significant impact in the future. of key importance will be the achievement of performance targets, because module efficiencies of at least 15% are probably necessary in the long term for photovoltaics to have a significant impact in grid‐connected applications. Strategies for achieving these performance levels with mediocre material quality and only moderate surface passivation and light trapping are presented. the challenges associated with the supporting substrate choice and layer depostion techniques and structures are discussed and the psesent practices reviewed. Important considerations include device performance, cost, throughput, device area and simplicity of fabrication and operation. Promising efficiencies in the vicinity of 15% have already been demonstrated using a number of different crystalline silicon layer‐formation techniques. Novel device structures based on incorporation of narrow bandgap materials (Si/Ge alloys) or defect layers, quantum wells and the impurity photovoltaic effect are considered, with particular emphasis given to approaches that compensate for the current loss in thin‐film cells. It appears increasingly likely that polycrystalline silicon thin‐film solar cells will have an impact on the development of photovoltaics in the future and may in fact provide the means for the substantial cost reductions necessary for significant penetration into utility markets.