Significantly enhanced coupling to half-space irradiation using a partially capped nanowire for solar cells

Abstract

Single nanowire solar cells are of great interests due to their promising prospects as nano-electronic power sources. Here, we propose a semiconductor nanowire partially covered with a dielectric cap. We demonstrate that with an appropriate degree of the coverage, the partially capped nanowire (PCNW) exhibits strongly enhanced light harvesting in comparison with the bare nanowire (BNW) and core-shell nanowire (CSNW). The enhancement can be attributed to reshaping the radiation patterns due to the symmetry breaking and the strong coupling between the incident light from the upper half space and the leaky mode resonance. We find that the absorption cross section of the PCNW structure integrated over whole space satisfies the fundamental absorption limit, and agrees with the transient coupled-mode theory. We also show that the angle range with high absorption can be adjusted through tuning the degree of coverage. Great increase in short-circuit current and open-circuit voltage enable the PCNW to possess a high power conversion efficiency of 55.31%, which is 141% and 42.7% increase in comparison with that of the BNW (22.95%) and CSNW (38.76%), respectively. The array composed of PCNW also displays superior light absorption and emission efficiency characteristics in comparison with those composed of BNW, CSNW, and the unstructured films. The cap makes the PCNW solar cell a promising candidate for diverse integrated nanosystems, such as photodetectors, nanoelectronic power sources, and super miniature cells.