Submicrometer gratings for solar energy applications

Material costs may be reduced and electrical properties improved by utilizing thinner solar cells. Light trapping makes it possible to reduce wafer thickness without compromising optical absorption in a silicon solar cell. In this work we present a comprehensive comparison of the light-trapping properties of various bi-periodic structures with a square lattice. The geometries that we have investigated are cylinders, cones, inverted pyramids, dimples (half-spheres), and three more advanced structures, which we have called the roof mosaic, rose, and zigzag structure. Through simulations performed with a 20 μm thick Si cell, we have optimized the geometry of each structure for light trapping, investigated the performance at oblique angles of incidence, and computed efficiencies for the different diffraction orders for the optimized structures. We find that the lattice periods that give optimal light trapping are comparable for all structures, but that the light-trapping ability varies considerably between the structures. A far-field analysis reveals that the superior light-trapping structures exhibit a lower symmetry in their diffraction patterns. The best result is obtained for the zigzag structure with a simulated photo-generated current Jph of 37.3 mA/cm2, a light-trapping efficiency comparable to that of Lambertian light-trapping.

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“…This argument is similar in nature to the one of Ref. 9. The results we see here also match well with what has been suggested recently by Refs.…”

Section: A Interpretation Of Resultssupporting

confidence: 93%

“…Such structures have been thoroughly analyzed in the past, [8][9][10] but have attracted renewed attention lately. [11][12][13][14] Recently, it has been shown that periodic structures may increase light trapping beyond that of the Lambertian 4n 2 limit, 15,16 but with a significant angular dependency.…”

Section: Introductionmentioning

confidence: 99%

Comparison of periodic light-trapping structures in thin crystalline silicon solar cells

Gjessing

Sudbø

Marstein

2011

Journal of Applied Physics

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“…In this case, the only way to assess absorption enhancement is by rigorous numerical solution of Maxwell's equations for the multilayer structure, taking into account the exact nature of all interfaces. Based on such techniques, significant absorption enhancement has been predicted for binary and ideally blazed gratings; [29][30][31] tailoring of surface textures for solar cells is still a rather young field. 32 Moreover, not all theoretically imaginable shapes are also feasible for solar cell processing.…”

Section: Resonance Excitation In Periodic Devicesmentioning

confidence: 99%

Resonances and absorption enhancement in thin film silicon solar cells with periodic interface texture

Haug

Söderström

Naqavi

et al. 2011

Journal of Applied Physics

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We study absorption enhancement by light scattering at periodically textured interfaces in thin film silicon solar cells. We show that the periodicity establishes resonant coupling to propagating waveguide modes. Ideally, such modes propagate in the high index silicon film where they are eventually absorbed, but waveguide modes exist also in the transparent front contact layer if the product of its refractive index and thickness exceeds half the wavelength. Taking into account that the absorption coefficient of realistic transparent conducing films exceeds the one of silicon close to its band gap, certain waveguide modes will enhance parasitic absorption in the transparent front contact. From an analysis based on the statistic distribution of energy among the available waveguide and radiation modes, we conclude that conventional thin film silicon solar cells with thick and nonideal contacts may fail to reach the previously noted bulk limit of 4n 2Si ; instead, a more conservative limit of 4 n 2 Si À n 2 TCO À Á applies.

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“…For the case of mono-crystalline silicon, periodic photonic nanostructures have been barely investigated optically but they have not been integrated in a solar cell so far [17][18][19][20][21][22].…”

mentioning

confidence: 99%

Photonic assisted light trapping integrated in ultrathin crystalline silicon solar cells by nanoimprint lithography

Trompoukis

Daïf

Depauw

et al. 2012

Applied Physics Letters

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We report on the fabrication of two-dimensional periodic photonic nanostructures by nanoimprint lithography and dry etching, and their integration into a 1-μm-thin monocrystalline silicon solar cell. Thanks to the periodic nanopatterning, a better in-coupling and trapping of light is achieved, resulting in an absorption enhancement. The proposed light trapping mechanism can be explained as the superposition of a graded index effect and of the diffraction of light inside the photoactive layer. The absorption enhancement is translated into a 23% increase in short-circuit current, as compared to the benchmark cell, resulting in an increase in energy-conversion efficiency.

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Submicrometer gratings for solar energy applications

Cited by 353 publications

References 11 publications

Comparison of periodic light-trapping structures in thin crystalline silicon solar cells

Comparison of periodic light-trapping structures in thin crystalline silicon solar cells

Resonances and absorption enhancement in thin film silicon solar cells with periodic interface texture

Photonic assisted light trapping integrated in ultrathin crystalline silicon solar cells by nanoimprint lithography

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