Fangwang Gou

Broadband absorption enhancement in ultrathin-film solar cells by combining dielectric nanogratings and metallic nanoribbons

Abstract. Optical absorption improvement and cost reduction of thin-film solar cells have been long-time issues. These two aims are achieved simultaneously by combining metallic nanoribbons and dielectric gratings at the front side of ultrathin-film amorphous silicon solar cells. Surface-plasmon-polariton waves excited by the nanoribbons at the long wavelength co-operates with Uller-Zenneck waves and cavity resonances excited by the gratings at the short wavelength with little cross-effect, leading to a complementary absorption enhancement of 31% when compared to planar structure. In addition, this design exhibits wide-angle absorption as well as a high fabrication tolerance. Compared to the previous work combining different mechanisms, this design provides fewer fabrication steps and an easier approach. Moreover, the nanoribbons can be used as a transparent conducting electrode for a low-cost alternative to expensive indium tin oxide thin-film.

Beam Steering with Nanoring Reflectarray Metasurfaces

One type of nanoring reflectarray metasurface is demonstrated to achieve high-efficiency beam steering in anomalous reflections. Rings with varied inner radius are designed to manipulate the phase front of the incident wave. The efficiency of anomalous reflections achieves more than 80% at the reflection angle of 53° under normal incidence. The light reflects along the surface of structure when the incident angle reaches to 12°. The anomalous reflection beams have the same polarization with the incoming light. This proposed structure can be applied in the high-efficiency waveplates, modulators, and couplers.

Absorption enhancement of a-Si thin film solar cells through surface plasmon polaritons and cavity resonance

A back metallic binary-rectangle grating is proposed to realize absorption enhancement through introducing plasmonic modes and cavity resonance modes. The grating contains a secondary grating whose height is optimized. Adding the structure can enhance absorption by a factor of 2.6 at λ = 915 nm and for the wavelengths in the range 550-790 nm, 875-900 nm the absorption is also enhanced.

A Design of a-Si Thin Film Solar Cell with A Dual Grating for Long Wavelength Absorption Enhancement

A structure combined dual diffraction grating is investigated. Great enhancement at the discussed wavelength rang can be seen. The maximum enhancement rate can reach 25 at the wavelength of 950 nm and enhancement is broadband.

The effect of transparent conductive oxides background spacer layer on light trapping in thin film solar cells

The influence of optical absorption in thin film solar cells induced by the transparent conductive oxide (TCO) spacer layer was numerically investigated. The paper results provide a guideline for designing TCO spacer layer.

Thin film solar cells based on cavity enhanced grating structure

A cavity enhanced one-dimensional grating structure is proposed to improve the light absorption within the α-Si thin film solar cell. Typically, dielectric or metal structure including gratings is added for the light absorption enhancement. Not only does the structure form the guided modes, and increase the surface area/surface angle, but also the thin film itself forms a cavity allowing light trapping for better absorption. However, the structure is optimized in these two mechanisms separately. In this paper, finite element method (FEM) was used to optimize thicknesses of two cavities and then combine them into a one –dimensional grating structure. Comparing to the flat thin film solar cell, we have get absorption enhancement factors of 1.12 and 1.51 normalized for the AM 1.5 spectrum for 300 nm to 950 nm by the two proposed structures.

Absorption enhancement for solar cells structured with quasi-periodic grating

Solar cells structured with quasi-periodic and periodic gratings are investigated. A broadband great enhancement can be observed. The quasi-periodic grating design is based on Fourier transform.

Hybrid Gratings for Complementary Absorption Enhancement in Ultra-thin Film Solar Cells

Amorphous silicon ultra-thin film solar cells with hybrid plasmonic and dielectric gratings on the surface of the active layer are studied numerically. Their respective advantages are combined to achieve the complementary absorption enhancement.

Dual-Cavity Resonance for Broadband and Wide angle Absorption Enhancement in Thin Film Solar Cells

A grating structure based on cavity resonance was proposed to broadband light absorption enhancement in a-Si thin film solar cells. Dual-cavity resonance is excited for better light harvesting especially in long wavelength range.

High performance absorber structure using subwavelength multi-branch dimers

As the desire growing of the thin film absorption structure for various sub-wavelength applications such as photo detector, thin-film thermal emitters, thermo photovoltaic cells, and multi-color filters, we proposed a type of subwavelength multi-branch dimers which exhibit several tunable dipole-dipole-like plasmonic resonances and integrated it into metal-insulator-metal structure as the top layer. The structures are studied through numerical calculation by finite element method. When normal incident is considered, the novel structure shows three absorption peaks in the considered wavelength range. One peak has near-perfect absorption and the other two also show excellent absorption.. When different angle oblique incident is considered, the absorption only has slight change, which is useful to an ultrathin absorber structure. In addition, we find that the thickness of the dielectric layer can tune the absorption rates for each absorption peak. In general, the multi-branch dimers can easily tune its absorption rates and spectrum via the change of their geometric parameters such as branch lengths, branch angles, and dielectric layer thickness.