Chuanhong Liu

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.

Double grating antireflection nanostructure based on nano-cone

A type of half-embedded cone grating nanostructure is proposed for antireflection (AR). It can achieve reflectance of down to 0.5% under normal incidence and 6% under incidence angle as large as 40 degrees in the 300-1100 nm wavelength range. Besides, it can maintain good performance in a large dimension range with a fixed period or vertex angle. Furthermore, the refractive index of the grating can be varied in a large range while keeping the high antireflective ability, namely that the material of the grating can be freely chosen without the limitation of single material. More importantly, it can tolerates the interlayer between the double cone grating much with just a slightly fluctuation of the reflectance less than 0.03%. These properties reduce both the design difficulty and the fabrication difficulty, making it a potential solution for use in various applications such as renewable energy and optical-electro devices.

Multiple-level grating used for nanostructured thin film solar cells

Surface recombination plays a key role in hign efficiency nanostructured thin film solar cells. How to reduce the recombination in a nanostructured cell or further increase absorption without increase of surface recombination is meaningful in solar cell design. We further increases light absorption without increase of surface recombination, and the extra light absorption contribute to the device efficiency. This concept of multiple-level grating shows significant importance in effective nanostructure light trapping.

Shape-induced effect on c-Si thin film solar cell efficiency

Nanophotonic light trapping methods play a key role in high thin film solar device. Even many parameters are discussed in cell designs; the shape of the semiconductor grating is rarely included. In this paper, we investigated the shape-induced effects on the absorption of solar cell and demonstrated that even for the structures at the nanometer scale; the shape of the grating is also an indispensable consideration for solar cells.

Combination of Ag nanoparticles and conformal triangular gratings in a-Si thin film solar cells

Conformal triangular gratings embedded Ag nanoparticles for thin film a-Si solar cells are studied numerically. With appropriate location they can work cooperatively to enhance light absorption in the long range of 750-900 nm.

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.