Optimization and optical characterization of vertical nanowire arrays for core-shell structure solar cells

- Regular nanowire arrays have been fabricated by MACE coupled with NLS.
- Optimization of nanowire geometry for a good light trapping.
- Structural variations lead to improved anti-reflection properties.
- Optical model for imperfect nanowire arrays has been developed.

In this work we study optical properties of vertical silicon nanowire (SiNW) arrays fabricated using metal assisted chemical etching (MACE) coupled with nanosphere lithography (NSL). We have studied optimal configurations minimizing total reflectance of 2 µm long SiNW arrays by modeling and compared their performance with experimental data. Fabricated SiNW arrays have shown lower total reflectance than modeled perfectly periodic ones. This has been found to be due to a variation of NW geometry and the presence of domains caused by the self-assembly during NSL process. We have developed a statistical model (based on rigorous coupled wave analysis) describing geometry variations and also demonstrated that different domains have rotated diffraction pattern with respect to their symmetry axes. The statistical model has been successfully validated on total reflectance and normalized Mueller matrix data. Furthermore, we have found that a very high light trapping can be achieved for nanowires only 125 nm long (Jsc equivalent of up to 42 mA/cm2), which can be exploited in thin and ultra-thin Si solar cells.