Optimal design for antireflective Si nanowire solar cells

We suggest a design guideline that optimally combines light absorptance and electrical performance in silicon nanowire (SiNW) solar cells. The design was experimentally developed using a tradeoff relation between wire length and space-filling ratio. Increasing (or decreasing) the wire length decreases (or increases) the wire filling ratio required to achieve the same amount of light absorption. The superior antireflection characteristics of SiNW arrays stem from optical impedance matching. A wire length of 1.2 μm suppressed light reflection enough to obtain 99% absorptance at a filling ratio of 38%. A short length (∼500 nm) design using nanopillars rather than nanowires effectively diminished the surface and bulk recombinations to achieve a short circuit current of ∼30 mA/cm2 while maintaining good light absorptance.