Optical absorption in microstructured crystalline silicon thin films

Abstract

In Si solar cells, the cost of the Si wafer itself accounts for over 50 % of energy conversion; therefore, economic use of Si contributes significantly towards lowering cost. Thin-film (∼ 25 µm) crystalline Si (c-Si) solar cells films are ideally-suited for low-cost photovoltaics. These thin-film c-Si solar cells are manufactured through a wide range of industrial processes including epitaxial growth, smart-cut, and layer transfer. In these devices, weak optical absorption of Si fundamentally limits performance. Historically, several surface texturing mechanisms have evolved to enhance optical absorption in solar cells. Most of geometrical-optics based texturing mechanisms require etched features comparable to thin-film thickness. As a result, randomly-created subwavelength structures are finding increasing applications for reducing surface reflection as well as enhancing near IR absorption. We report on diffractive and physical optics mechanisms in enhancing absorption in thin Si films. Randomly-created subwavelength diffractive structures as well periodically-patterned deeply-etched subwavelength structures have been demonstrated to be highly effective in reducing reflection and creating broadband absorption using scattering and physical optics mechanisms.