Simulation of Optical Properties of the Si/SiO2/Al Interface at the Rear of Industrially Fabricated Si Solar Cells

The specular and diffuse reflection properties of sunlight at the rear surface of silicon solar cells with various degrees of roughness are computed by solving the Maxwell and material equations in two dimensions, using the COMSOL RF MODULE. The model is first tested on planar Si/SiO2/air interfaces, where perfect agreement with the Fresnel theory is attained within numerical precision. The chosen simulation domain is similar to typical experimental scattering measurements. A simulation with planar Si/SiO2/Al interfaces confirms an angular resolution of the specular beam of about 10°, and a lower resolution limit for scattering probability near 10. The simulations show that for wavelength of 800 nm, (i) maximum scattering is achieved with a standard deviation for roughness between 50 nmand 100 nm, (ii) the distribution probabilities for scattering are similar (but restricted to certain scattering angles) if roughness is produced by etching solely the grown SiO2 instead of the Si. Output parameters for geometrical ray tracers are computed.