Diffraction grating structures in solar cells

Abstract

Sub-wavelength periodic texturing (gratings) of crystalline-silicon (c-Si) surfaces for solar cell applications can be designed for maximizing optical absorption in thin c-Si films. The authors have investigated c-Si grating structures using rigorous modeling, hemispherical reflectance and internal quantum efficiency measurements. Model calculations predict almost /spl sim/100% energy coupling into obliquely propagating diffraction orders. By fabrication and optical characterization of a wide range of 1D and 2D c-Si grating structures, they have achieved broadband, low (/spl sim/5%) reflectance without an antireflection film. By integrating grating structures into conventional solar cell designs, they have demonstrated short-circuit current density enhancements of 3.4 and 4.1 mA/cm/sup 2/ for rectangular and triangular 1D grating structures compared to planar controls. The effective path length enhancements due to these gratings were 2.2 and 1.7, respectively. Optimized 2D gratings are expected to have even better performance.