Laterally assembled nanowires for ultrathin broadband solar absorbers

Abstract

We studied optical resonances in laterally oriented Si nanowire arrays by conducting finite-difference time-domain simulations. Localized Fabry-Perot and whispering-gallery modes are supported within the cross section of each nanowire in the array and result in broadband light absorption. Comparison of a nanowire array with a single nanowire shows that the current density (J(SC)) is preserved for a range of nanowire morphologies. The J(SC) of a nanowire array depends on the spacing of its constituent nanowires, which indicates that both diffraction and optical antenna effects contribute to light absorption. Furthermore, a vertically stacked nanowire array exhibits significantly enhanced light absorption because of the emergence of coupled cavity-waveguide modes and the mitigation of a screening effect. With the assumption of unity internal quantum efficiency, the J(SC) of an 800-nm-thick cross-stacked nanowire array is 14.0 mA/cm², which yields a ~60% enhancement compared with an equivalent bulk film absorber. These numerical results underpin a rational design strategy for ultrathin solar absorbers based on assembled nanowire cavities.

Three-dimensional grating nanowires for enhanced light trapping

“…Note that t 0 indicates bare NWs. The J SC increases with increasing t up to ∼100 nm, while a maximum is observed at a ∼ 400 nm, which is consistent with previous literature [25,28]. For the grating NW with a 400 nm, J SC was calculated as a function of t with and without a backside Ag reflector [ Fig.…”

“…In addition, the grating NW shows remarkable absorption at short wavelengths compared with the other structures. Notably, the enhancement in absorption is more significant for TE polarization, where the oscillation direction of the electric field is perpendicular to the NW axis [25].…”

“…2(b). The pronounced peaks exhibit an alternating absorption intensity along the NW Letter axis, which indicates that periodic shells convert a normal plane wave into transversely propagating waveguide modes [18,25]. On the other hand, the common peaks follow a simple Fabry-Perot mode oscillation.…”

Influence of wetting state on optical reflectance spectra of Si nanopillar arrays

“…The scattering and absorption cross-sections of individual sub-wavelength NPs are much larger than their geometrical cross-section due to Mie resonance. [10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27] The resonance wavelength depends on geometric parameters, such as diameter, length, and pitch of the array. As a result, NPs with different dimensions can display various colors.…”

“…[10][11][12][13][14][15][16][17] In addition, the Mie resonance as well as the gradual decrease of the refractive index and multiple scattering of the NP array enables broad-band and omnidirectional antireflection (AR) effects. [18][19][20][21][22][23][24][25] NP arrays also can exhibit the second-order-scattering-induced reflection divergence and nonlinear depolarization 26 and enhanced Stoke Raman scattering. 27 Therefore, varying geometrical configurations of the NP array will significantly modify their optical characteristics.…”