Design and growth of III–V nanowire solar cell arrays on low cost substrates

State-of-the-art III-V multijunction cells have achieved a record efficiency of 42.8%, which has fueled great interest in the utility sector for large-scale deployment. However, III-V solar cells have thus far proven too expensive for widespread terrestrial applications due to the combined cost of substrates, growth processes, and materials. Here, we propose a novel III-V solar cell based on the epitaxial growth of AlGaAs/GaAs on Ge nanowires, pre-patterned on low cost substrates to achieve cost-effective, large-scale deployment. This approach is based on our recent discovery that the surface kinetics and epitaxial growth by MBE and MOCVD are dramatically altered when growing on nanostructures instead of planar surfaces. These growth kinetics enable uniform, single crystal growth of low-defect, lattice mismatched materials on nanostructures with high aspect ratios. We present the device design, TCAD simulation results, and experimental growth results for GaAs/Ge core-shell nanowires on silicon substrates. Finite-difference time-domain (FDTD) simulation results show that this GaAs/Ge nanowire array has reduced reflection and wider incident angle acceptance than its planar counterpart, and outperforms planar anti-reflective coatings under some conditions. GaAs is epitaxially grown on Ge nanowires via MBE and MOCVD. TEM measurements on the wires confirm that the GaAs/Ge core-shell structure is single crystal. Based on these results, we are in the process of fabricating GaAs/Ge nanowire solar cell arrays. We will present further characterization of these core-shell arrays as well as electrical measurements of solar cell devices.