Three dimensional crystalline silicon solar cells

Baytemir, Gülsen
Three-dimensional crystalline silicon solar cells have been attracting attention with its remarkable electrical and optical performance. In this geometry, nano/micropillars allow minority carrier collection in the radial direction and shorten the path length of the photogenerated carriers. Furthermore, with appropriate geometry of the pillars the solar cell efficiency is enhanced due to the reduced surface reflectance and increased light harvesting. Throughout this study, metal assisted etching (MAE), a top-down method was applied through photolithography to fabricate micropillars. Firstly, radial junction cells with different micropillar lengths, including the longest ~6 µm, were fabricated by applying different etching durations. The maximum efficiency value, 15.90 %, was obtained from the cell with longest micropillars since with the increase in pillar length, higher Jsc values were obtained due to the reduced surface reflection and higher junction area. Radial and planar junction solar cells were then fabricated using Si wafers contaminated with Au impurities having U-shape diffusion profile in Si. The efficiencies of the radial junction solar cells, which allow photogenerated carriers to be collected over shorter distances, were less affected by contamination than planar junction solar cells. This is consistent with the expectation that the cells with radial geometry are less sensitive to the quality of the material used. Moreover, the solar cells with different thicknesses were fabricated to increase the proportion of the region containing micropillars in the cell and to reduce the fabrication cost by allowing the use of thin Si substrates. Firstly, longer micropillars were obtained by increasing HF concentration in the MAE solution to suppress the lateral etching and instead of H2O, using ethanol which has a lower surface tension to obtain smooter etching. The efficiency value of 17.27 %, one of the highest efficiency values in radial junction cells, was obtained from the cell containing 11.5 µm micropillars. By decreasing the thickness of the cells, it was observed that the efficiency values were less affected in three dimensional solar cells than in planar junction cells due to less decrease in Voc and Jsc values.


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Citation Formats
G. Baytemir, “Three dimensional crystalline silicon solar cells,” Ph.D. - Doctoral Program, Middle East Technical University, 2018.