Epitaxial GaAsP/Si Tandem Solar Cells with Integrated Light Trapping

We investigate the effect of Si random pyramid texturing on 1.7eV/1.1eV GaAs0.77P0.23/Si 2-terminal tandem solar cells (hereafter GaAsP/Si). Due to the light trapping effect, rear surface texturing increases the short-circuit current density of the Si bottom cell by 2.76 mA/cm2 relative to an untextured cell. For the GaAsP top cell, we investigate the use of lattice-matched AlGaAsP as the back surface field (BSF) layer and also as an intermediate barrier between the n-GaAsP emitter and n-AlInP window. Despite parasitic absorption in the n-AlGaAsP barrier, our 1.0 cm2 GaAsP/Si tandem cell with backside textured Si bottom cell exhibits an NREL-certified AM1.5G efficiency of 18.7%. A reduction of device area from 1.0 cm2 to 0.13 cm2 results in an efficiency of 19.5% due to lower series resistance. Development of u003e20%-efficient tandem cells is ongoing.