Sidewall Profile Dependent Nanostructured Ultrathin Solar Cells With Enhanced Light Trapping Capabilities

Abstract

Theoretical studies of ultra-thin silicon solar cells with cylindrical, conical and parabolic surface nanostructures inherited from natural self-assembled anodic alumina oxide (NSA-AAO) were performed by finite-difference time-domain (FDTD) method. All nanostructured solar cells obtained an optimized efficiency enhancement as high as more than 33% comparing with that of the anti-reflective (AR) one. Numerical results reveal that the range of efficient structural parameters for the nanostructured (e.g., cylindrical) solar cell can be effectively enlarged as the period of the nanostructure changes from 0.1 μm to 0.5 μm. Moreover, the improvements of absorption photocurrent density (Jph) in conical and parabolic nanostructured solar cells are comparable with the cylindrical nanostructured one but less sensitive to the fill factor and structural height in the whole simulation region of 0.1-0.9 and 0-0.25 μm, respectively. Equivalent refractive index models were used to analysis the antireflection performance of surface nanostructures from the point of view of sidewall profiles. Resonance modes induced through nanostructures have greatly improved the absorptance of solar cells in broadening wavelength bands which consequently raised the Jph. This study serves as a way for the practical design and application of AAO nanostructure based high-efficiency ultra-thin solar cells.

High Anti-Reflection Large-Scale Cup-Shaped Nano-Pillar Arrays via Thin Film Anodic Aluminum Oxide Replication

“…The first one is to acquire a desired f and let the n eff satisfy n eff = √ n i n s , which is applicable for the vertical side-wall profile situation [ 17 , 24 ]. The other one is to tailor the side-wall profile of the nano-pillar to make a gradually changed equivalent refractive index along the pillar direction [ 27 ], like the CSNP structure proposed in this work. Figure 4 b shows the polarization-dependent angle reflectance curves; no obvious polarization dependent properties can be seen for both single-polished Si and CSNP Si.…”

“…The calculation of J ph represents the quantitative measurement of the nanostructured solar cell light-trapping ability [ 55 ]. Under the condition of solar radiation AM1.5, the J ph can be obtained by the following formula [ 27 , 28 ]: where e is the electron charge, h is the Planck constant, c is the speed of light in vacuum, I AM1.5 ( λ ) is the incident light spectrum AM1.5, A( λ ) represents the absorption of solar energy by Si, R( λ ) represents the reflection, and T( λ ) represents the transmission.…”

“…In order to establish the light trapping performance of CSNP, Table 1 lists the optimized J ph with different structural parameters of the solar cells in this study and those of recent literature as a reference [ 27 ]. The same parameters, such as device model, structure height, period, and fill factor, have been studied in the reference work so the comparison can be applicable.…”

“…Inspired by the anodic aluminum oxide (AAO) pattern fabrication process [ 26 ], self-assembled nanostructure replication method has been proven to be an effective nanoscale solution for lithography-free, low cost, large area, and high throughput [ 24 , 27 , 28 , 29 ]. The excellent properties of self-assembled nanostructures can be obtained by large area adjustment of the geometric appearance; for example, the pore size, hole spacing, etc., can be continuously adjusted from tens of nanometers to hundreds of nanometers [ 24 , 30 , 31 , 32 ].…”

“…Therefore, a thin film solar cell model was built to further study the light-trapping performance of the CSNP. The absorption of the CSNP-structured solar cell was greatly enhanced in the whole wavelength of 0.3–1.1 μm and showed even higher performance than the regular nanostructure (like cylinder, cone, and parabola) [ 27 ] solar cells. These results suggest that the CSNP could serve as an efficient AR structure and can be used to the application of high-performance optical components and devices.…”