Periodic Upright Nanopyramids for Light Management Applications in Ultrathin Crystalline Silicon Solar Cells

Abstract

Silicon wafers account for approximately 61% of the price of today's silicon solar cells [1]. For the primary benefit of reduced material cost [2], [3], the thickness of industrial silicon wafer solar cells has been reduced to ∼180 <italic>μ</italic>m and is expected to continue decreasing. New technologies to produce thin and kerfless wafers with disruptive potential [4] have enabled high-performance thin silicon solar cells with thicknesses less than 50 <italic>μ</italic>m. For instance, the company Solexel has achieved 21.2% efficiency with 35 <italic>μ</italic>m silicon thickness [5]. Laboratory studies explored thicknesses down to 20 <italic>μ</italic>m by wafer thinning or epitaxial growth [2], [3], [6], [7].

This emerging concept of ultrathin silicon solar cell is also motivated by a few other benefits including better tolerance in material quality [2], [7], likely higher open-circuit voltage [3], [8]– [10], and possibilities for novel flexible designs [11], [12]. The technological innovations developed for thinner wafers such as directly growing epitaxial wafers from gas [13], directly producing wafers from molten silicon without casting [14], [15], and diamond wire sawing [16] also reduce the Capex, offering great growth impetus to the photovoltaic industry [17].

In contrast, the reduction in the thickness of silicon absorber layers also comes with two crucial issues: First, a thin silicon solar cell is faced with lower optical absorption than a typical wafer solar cell, as the average absorption length in the active layer is reduced; second, the conventional micron-scale pyramid textures including random upright pyramids and inverted pyramids cannot be directly transferred to ultrathin silicon solar cells with only a few micrometers thickness.

Citation

Wang, P., Liu, Z., Xu, K., Blackwood, D.J., Hong, M., Aberle, A.G., Stangl, R. and Peters, I.M., 2017. Periodic Upright Nanopyramids for Light Management Applications in Ultrathin Crystalline Silicon Solar Cells. IEEE Journal of Photovoltaics, 7(2), pp.493-501.

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Categories: Solar & Photovoltaics