Capacitance-Voltage Characterization Technique Adapted to Tandem Solar Cell

Abstract : This paper presents a simple and non-destructive method to determine doping densities and built-in potential of subcells by adapting the well-known capacitance-voltage (C-V) technique to two-terminal (2T) tandem solar cells. Because of the electrical coupling between the two subcells in a monolithic 2T tandem solar cell the standard method using a Mott-Schottky plot (1/C 2 vs. V) cannot be applied. Using numerical modeling, it is demonstrated that, by under chosen illumination conditions where only one subcell can absorb the light, it is possible to explore the bias dependence of the capacitance and to extract the parameters of the other subcell if the appropriate frequency conditions are present. This method is experimentally applied to an AlGaAs/Si tandem cell and parameters of both AlGaAs and Si cells are extracted. Finally, the validity of that method is assessed by the very good agreement obtained when comparing the values extracted from our measurements on the tandem cell to those extracted from measurements on isotype cells and to the values targeted during the fabrication process of the AlGaAs/Si tandem solar cell.