Funnel-shaped silicon nanowire for highly efficient light trapping

Abstract

In this Letter, funnel-shaped silicon nanowires (SiNWs) are newly introduced for highly efficient light trapping. The proposed designs of nanowires are inspired by the funnel shape, which enhances the light trapping with reduced reflections in the wavelength range from 300 to 1100 nm. Composed of both cylindrical and conical units, the funnel nanowires increase the number of leaky mode resonances, yielding an absorption enhancement relative to a uniform nanowire array. The optical properties of the suggested nanowires have been numerically investigated using the 3D finite difference time domain (FDTD) method and compared to cylindrical and conical counterparts. The structural geometrical parameters are studied to maximize the ultimate efficiency and hence the short-circuit current. Carefully engineered structure geometry is shown to yield improved light absorption useful for solar cell applications. The proposed funnel-shaped SiNWs offer an ultimate efficiency of 41.8%, with an enhancement of 54.8% relative to conventional cylindrical SiNWs. Additionally, short-circuit current of 34.2 mA/cm2 is achieved using the suggested design.

Recent Trends in Plasmonic Nanowire Solar Cells

“…In addition, Ko et al [71] demonstrated that an ultimate efficiency of 28.9% can be obtained by decreasing the cone bottom diameter to 20 nm. Further, the SiNWs funnel shape achieved an ultimate efficiency of 41.8% [29].…”

“…In this study, λ g is taken as 1100 nm, corresponding to the energy gap of the silicon material. The short-circuit current density (J sc ) is related to the ultimate efficiency by assuming perfect carrier collection efficiency, i.e., each photon absorbed with energy higher than the bandgap produces one electron-hole pair, and all generated carriers are collected to produce current without recombination losses [28,29]. The short-circuit current density J sc of the proposed design can be expressed as [29] J sc = η The open-circuit voltage can be related to the maximum short-circuit current density by [75]:…”

“…Additionally, the proposed design offers continuous reflections between the SiNWs until the incident angle becomes smaller than the critical angle resulting in high light trapping and broadband absorption. Furthermore, the absorption enhancement can be also explained from the waveguide modal dispersion of the NWs [29]. The leaky mode resonance relies on the NW diameter.…”

“…The absorption of the Si NW funnel design [29] without plasmonic material is also plotted in Figure 4. It may be noted from this figure that the absorption through the plasmonic metal is small.…”

“…The textured silicon surface structures can be etched by various etchants, such as NaOH [21], TMAH [22,23], and KOH [24]. Different textured structures have been introduced, including the pyramidal textured surfaces [25], inverted pyramidal [26], honeycomb [27], nanowire [28,29], gratings [30], V-grooved [31], and other types of structures [32][33][34]. Most of these structures have large size and are not suitable for thin-film SCs with micrometer or sub-micrometer ranges [30].…”