Parameterization of the Back-Surface Reflection for PERC Solar Cells Including Variation of Back-Contact Coverage

Simulation is essential for a comprehensive analysis of the performance of solar cells. The rear contact pitch of passivated emitter and rear cells (PERC cells) is a crucial device parameter that influences not only the electrical performance but also the optical performance of these cells. This article investigates the applicability of the analytical light trapping model by Basore to account for the optical influence of the rear contact pitch as a simpler alternative to ray tracing. First, we manufacture three different groups of cells with different rear contact pitches, where the metallization fraction f
_met
varies between 0 and 54%. Second, the reflectance of the cells is measured. Subsequently, we fit the model parameters R
_f
and R
_b
(internal reflection on the front and back surface, respectively) to the measured reflectance. While we confirm a nonlinear relation between f
_met
and the measurable spectra found in previous works, our results reveal linear relations between f
_met
and R
_b
with the adjusted coefficients of determination of R
_adj
²
> 0.97, as well as between f
_met
and the charge carrier generation rates with R
_adj
²
> 0.94. These relations allow a simple and rapid optical simulation of f
_met
variation for PERC cells. The same approach is likely applicable to any local contacts also in other cell concepts.