Enhanced short-circuit current density in epitaxial InGaP/GaAs/Si triple-junction solar cells enabled by wide bandgap n-AlGaAs buffers

Epitaxial integration of III−V solar cells on a silicon substrate offers large-scale, relatively low-fabrication cost, and high-efficiency photovoltaics. However, challenges remain in realizing wide bandgap III-V buffers with low threading dislocation density (TDD) and low parasitic absorption. To address the issues, we explore the epitaxial growth of n-Al_xGa_1-xAs (x = 0, 0.05, 0.10) buffers on Si to enhance short-circuit current (J_sc) of the III-V/Si tandem cells. Photoluminescence measurements confirm an increased bandgap of 1.55 eV for n-Al_0.10Ga_0.90As buffer. Higher Al composition increases the TDD while the buffer roughness remains almost constant. Notably, the 1.55 eV n-AlGaAs buffer achieves a TDD of 2.5 × 10⁷ cm⁻² with two asymmetric step-graded filters. As a proof of concept, GaAs/Si tandem and InGaP/GaAs/Si triple-junction cells achieve enhanced J_sc of 8.0 and 8.5 mA/cm², respectively. This study demonstrates the feasibility of high bandgap n-Al_xGa_1-xAs buffers to enhance the J_sc in Si bottom cells, advancing the development of high-efficiency, low-cost III-V/Si multi-junction solar cells.