Absorption enhancement in thin-film silicon solar cells in SOI configuration using physical and geometrical optics

High performance in crystalline thin (∼ 10 μm) film silicon solar cells requires complete optical absorption over its spectral range. Geometrical schemes are ineffective due to their large feature dimensions. Enhanced optical absorption can be achieved through two mechanisms based on diffractive and physical optics. In diffractive approach, light confinement is achieved through obliquely propagating transmission orders that effectively fill the frequency space. In the physical optics approach, rigorous coupled wave analysis is used to calculate optical absorption in subwavelength grating structures based on wave guiding mechanism, A 10-μm thick Si film in SOI configuration was chosen to perform a comparative evaluation of these two approaches. Optical transmission of planar Si films was compared with randomly textured and deeply etched two-dimensional gratings structures. Transmission from random structures was diffuse and translucent, while that from gratings, was weak and wavelength-dependent. Although SOI substrates are not practical for large-scale manufacturing, they have been determined to highly effective for understanding and optimizing optical transmission and device performance.