Doubling Absorption in Nanowire Solar Cells with Dielectric
Shell Optical Antennas
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Abstract
Semiconductor
nanowires (NWs) often exhibit efficient, broadband
light absorption despite their relatively small size. This characteristic
originates from the subwavelength dimensions and high refractive indices
of the NWs, which cause a light-trapping optical antenna effect. As
a result, NWs could enable high-efficiency but low-cost solar cells
using small volumes of expensive semiconductor material. Nevertheless,
the extent to which the antenna effect can be leveraged in devices
will largely determine the economic viability of NW-based solar cells.
Here, we demonstrate a simple, low-cost, and scalable route to dramatically
enhance the optical antenna effect in NW photovoltaic devices by coating
the wires with conformal dielectric shells. Scattering and absorption
measurements on Si NWs coated with shells of SiN<sub><i>x</i></sub> or SiO<sub><i>x</i></sub> exhibit a broadband enhancement
of light absorption by ∼50–200% and light scattering
by ∼200–1000%. The increased light–matter interaction
leads to a ∼80% increase in short-circuit current density in
Si photovoltaic devices under 1 sun illumination. Optical simulations
reproduce the experimental results and indicate the dielectric–shell
effect to be a general phenomenon for groups IV, II–VI, and
III–V semiconductor NWs in both lateral and vertical orientations,
providing a simple route to approximately double the efficiency of
NW-based solar cells