Optical Modeling of Alkaline Saw-Damage-Etched Rear Surfaces of Monocrystalline Silicon Solar Cells

In this study, we propose a geometric optical model to represent alkaline saw-damage-etched (SDE) surfaces of monocrystalline silicon wafers. An experimental study is carried out to characterize the optical properties of alkaline SDE surfaces on monocrystalline silicon wafers. Based on the surface characteristics measured by goniometry and height profiling, a geometric optical model is developed to describe the SDE surface with two parameters: characteristic angle and planar fraction. Using the path-tracing method, spectral reflectance simulations are carried out for four different types of samples. With the measured characteristic angle of 22° and planar fraction of 0.25 or 0.36, we find that this representation of SDE surface can predict the reflection and transmission with a root-mean-square error (RMSE) of the equivalent current density from 0.19 to 0.57 mA/cm². The developed model is also applied to the optical loss analysis of aluminum local back surface field (Al-LBSF) solar cells with an SDE rear surface. We find that SDE rear surfaces provide better light trapping than planar surfaces. As a consequence, Al-LBSF solar cells with pyramids on the front and an SDE rear are predicted to produce 0.6 mA/cm ² more photocurrent than similar cells with a planar rear surface.