3-dimensional optical model for thin film silicon solar cells

This paper addresses optical effects in small area thin film silicon p-i-n solar cells deposited on a glass/TCO substrate. An existing one-dimensional model was extended to three dimensions to include the effect of substrate glass thickness and lateral solar cell area. With its help we can model real laboratory cells where the cell dimensions are comparable to the glass thickness. For a quantitative evaluation we compare the external quantum efficiency of an infinitely large solar cell with small area cells. Here the modeling results show increasing differences with increasing glass thickness, decreasing cell area and improving light scattering properties of the TCO. This is explained by internal light trapping in the glass substrate, which causes loss or gain of light intensity absorbed in the cell area. Neglecting such effects can lead to about 11% error in short circuit current density calculated from quantum efficiency measurements.