Growth and characterization of GaAsP top cells for high efficiency III?V/Si tandem PV

We investigate the growth, microstructure and device characteristics of 1.71eV bandgap GaAs_0.76P_0.24 solar cells grown on Si substrates using Si_yGe_1-y graded buffers. Our optimized growth conditions suppress defect nucleation at the GaAsP/SiGe heterointerface and enable the demonstration of single junction solar cells with a threading dislocation density of 3.4×10⁶ cm^-2, a 3× reduction compared to reported GaAs_xP_1-x cells grown on Si. The solar cells have high open-circuit voltages (V_oc) of 1.22 V, bandgap-voltage offset (W_oc) of 0.48 V (representing a 45 mV reduction over prior art). The short-circuit current density (j_SC) is 11 mA/cm² and the fill factor (FF) 82%, under AM1.5G irradiance without an anti-reflection coating (ARC). Integration of an ARC would push these GaAs_0.77P_0.23 single junction solar cells to >15% efficiency, making them well suited to cascade with a Si solar cell for high efficiency tandem solar cells.