Direct-gap 2.1?2.2 eV AlInP solar cells on GaInAs/GaAs metamorphic buffers

AlInP offers the highest direct bandgap (Eg) among non-nitride III-V materials, making it attractive for top cell applications in 5-6 junction solar cells. We present novel 2.07-2.19 eV, direct-gap AlInP solar cells, grown on GaInAs/GaAs graded buffers by metal-organic chemical vapor deposition. Despite the high Al content of 36-39% in the active regions, SIMS results indicate oxygen concentrations less than 2.3×10¹⁶ cm^-3. The AlInP devices we present here exhibit superior photovoltaic performance to GaP and are comparable to metamorphic GaInP solar cells, reaching a Eg-voltage offset of 0.58 V. Design enhancements based on device and material characterization led to improvements of up to 65% in short circuit current density from our first-generation AlInP devices. The promising results in this work provide an alternative path towards realizing high-Eg top junctions with applications in upright metamorphic multijunction solar cells.