Temperature dependence of InGaP/GaAs/InGaAs concentrators using bifacial epigrowth

Recently, Spire Semiconductor has demonstrated a bifacial InGaP/GaAs/InGaAs concentrator cell that achieved a previous record of 42.3% at 406 suns, AM1.5D, 25°C. However, as concentrators in modules typically operate at significantly higher than room temperature (~65°C), the dependence of cell performance as a function of temperature is of great importance to module manufacturers. Here the temperature coefficients of current, voltage, and efficiency for the 42.3% bifacial tandems are presented. The 42.3% efficient cell, exhibits a Δeff/ΔT of -0.098%/°C that is higher than the that of the Ge based triple junction (-0.06%/°C), because ΔJ_sc/ΔT is negative for the bifacial tandems and it is positive for the Ge based junction. Based upon temperature dependent IV and QE measurements, the negative ΔJ_sc/ΔT coefficient is attributed to insufficient current in the InGaAs subjunction. Finally, we discuss improvements made to the InGaAs junction that significantly improve the ΔEff/ΔT coefficient to a value comparable to that observed for Ge based junctions.