Thin-film Solar Cells With Binary Grating

The thin-film solar cells have broad market prospect and is always the main research direction ofphotovoltaic technology because of its advantages: less material, flexible structure, and easy large-scaleproduction, and so on. For the thin-film solar cells, it is difficult to full absorb the incident sunlight becauseof its thin absorbing layer. Grating structures are etched in the surface of the thin-film solar cells. Theoptical path length in the thin absorbing layer increases because of diffraction, therefore the cell efficiencyis improved. At present, the phase grating of various structures are etched between the transparentconductive film and the silicon thin film. They are usually the research focus because of simple processand strong practicality.The morphology of the phase grating are always rectangular, but this grating only has high diffractionefficiency in a specific wavelength. The thin-film solar cells have a very wide band. How to improve thediffraction efficiency of all waves, especially in the longer wavelengths, has become an important researchcontent of the grating structure of thin film solar cells. The binary optics emerging in the mid1980sprovides a new idea for solving the problem. Binary optics is a new optical branch on the basis of thetheory of light diffraction, and it is a forefront subject formation from the crossing and infiltration of opticsand microelectronics technology. Experimental and computational results show that triangular morphologygrating has higher diffraction efficiency than the conventional rectangular morphology grating, but theincline etching process is not suitable for industrial production. In the binary optics technology, toapproximate the triangular grating cant with bench-shape outline has formed a complete design methodand production process. In this paper we make the binary grating apply to the grating structure of the thinfilm solar cells, respectively study the diffraction efficiency of different steps of the binary grating in the visible and near-infrared bands. The results show that, the binary grating have high diffraction efficiency inthe entire bands, this grating structure is used in the thin film solar cells, the conversion efficiency of thethin film solar cells can be further improved.The thin-film solar cells with binary grating to enhance the diffraction efficiency were introduced inthis article. Diffraction field distribution of the binary gratings with vertical incidence are calculated by theFourier transform of the grating transmission function. The zero-order diffraction intensity in the visibleand near infrared band and the total diffraction efficiency varying with the different wavelength of thebinary grating were calculated. Take the thin-film silicon solar cells for example, the intensity distributionof general phase grating, two-step and three-step binary gratings, changing law with the zero-orderdiffraction intensity and the diffraction efficiency were calculated. The results show that the totaldiffraction efficiency in wider wavelength bands could be enhanced greatly adopting binary gratingsstructure compare than using general phase grating.