Current-Matched III–V/Si Epitaxial Tandem Solar Cells with 25.0% Efficiency

III–V/Si epitaxial tandems with a 1.7-eV GaAsP top cell promise stable power conversion efficiencies above the fundamental limit of Si single-junction cells. However, III–V/Si epitaxial tandems have suffered from limited minority carrier diffusion length in the top cell, leading to reduced short-circuit current densities (J_SC) and efficiencies. While conventional wisdom dictates that dislocation density in III–V/Si tandems must be reduced to boost efficiency, here, we show that heterointerface design and growth sequence also play critical roles in reducing recombination losses. Our improved GaAsP cells make use of a wide-band gap AlGaAsP electron-blocking layer that forms a pristine interface with GaAsP, resulting in a 10%–20% (absolute) boost in quantum efficiency over previous work in the critical red wavelength range (600–725 nm), despite similar dislocation density. Combining the improved top cell carrier collection with Si backside texturing, we obtain 25.0% efficient GaAsP/Si tandem cells with a closely matched J_SC of 18.8 mA/cm². Tandem solar cells consisting of a GaAsP top cell grown on Si can potentially offer an ideal combination of stability and efficiency. However, GaAsP/Si tandem cells are typically hampered by crystalline defects. Improving the quality of interfaces surrounding the GaAsP cell enables Fan et al. to demonstrate a 25% efficient tandem device.