Design and growth of III-V on Si microwire array tandem solar cells

Tandem Ga_(1-x)In_xP/Si microwire array solar cells are a route towards a high efficiency, low cost, flexible, wafer-free solar technology. Coupled full-field optical and device physics simulations of a Ga_(0.51)In_(0.49)P/Si wire array tandem are used to predict device performance. A 500 nm thick, highly doped “buffer” layer between the bottom cell and tunnel junction is assumed to harbor a high density of lattice mismatch and heteroepitaxial defects. Under simulated AM1.5G illumination, the device structure explored in this work has a simulated efficiency of 23.84% with realistic top cell SRH lifetimes and surface recombination velocities. The relative insensitivity to surface recombination is likely due to optical generation further away from the free surfaces and interfaces of the device structure. To move towards realizing these device structures, GaP and Ga_(1-x)In_xP layers were grown heteroepitaxially with metalorganic chemical vapor deposition on Si microwire array substrates. The layer morphology and crystalline quality have been studied with scanning electron microscopy and transmission electron microscopy, and they provide a baseline for the growth and characterization of a full device stack.