Wide-bandgap metamorphic InyGa1-yP solar cells

Summary form only given: We have grown metamorphic In_0.39Ga_0.61P solar cells on optimized GaAs_0.8P_0.2/GaAs graded buffers via solid source molecular beam epitaxy to serve as the top cell in a multi-junction device. Calculations show that the incorporation of a 2.00-2.20 eV top cell into future 4-6 junction cells could enable efficiencies as high as 60%. We show that faceted trenches, a morphological defect formed during growth of the tensile-strained GaAs_xP_1-x graded buffers, led to local quenching of radiative recombination in forward-biased solar cell structures. Transmission electron microscopy revealed phase separation in the In_yGa_1-yP active region, regardless of composition, while selected area diffraction patterns showed a lack of Cu-Pt ordering. Although the disordered structure aids in the goal of attaining a wide bandgap, we speculate that phase separation has a detrimental effect on the ultimate open circuit voltage, due to the contribution of the lower-bandgap, In-rich regions to the dark current. Through optimized growth of GaAs_xP_1-x graded buffers, we produced 2.00 eV, metamorphic In_0.39Ga_0.61P solar cells free of faceted trenches that exhibited open circuit voltages as high as 1.42 V. These results indicate that metamorphic In_yGa_1-yP is a promising material for future multi-junction solar cells.