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 GaAs0.76P0.24 solar cells grown on Si substrates using SiyGe1−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 GaAsxP1−x cells grown on Si. The solar cells have high open-circuit voltages (Voc) of 1.22 V, bandgap-voltage offset (Woc) of 0.48 V (representing a 45 mV reduction over prior art). The short-circuit current density (jSC) 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 GaAs0.77P0.23 single junction solar cells to >15% efficiency, making them well suited to cascade with a Si solar cell for high efficiency tandem solar cells.