Numerical simulations of triple-junction GaInP/GaAs/Ge solar cells to provide insight into fill-factor losses at high concentration

We have modeled a Ga_0.5In_0.5P/GaAs/Ge triple junction solar cell, including two Esaki diodes, to analyze how performance changes with illumination intensity. As has been observed experimentally, fill factor (FF) is the primary aspect of performance that limits efficiency at high concentration levels. The FF decreases because of series resistance and barriers created by the GaAs/GaInP back surface field. By adjusting carrier concentration or the material associated with the back surface field (BSF) and the carrier concentration in the absorber, FF losses can be reduced and efficiency enhanced at high concentration levels.