GaInP/GaInAs/GaInNAs/Ge Four-Junction Solar Cell Grown by Metal Organic Chemical Vapor Deposition with High Efficiency

We directly grow a lattice matched GaInP/GaInAs/GaInNAs/Ge (1.88 eV/1.42 eV/1.05 eV/0.67 eV) four-junction (4J) solar cell on a Ge substrate by the metal organic chemical vapor deposition technology. To solve the current limit of the GaInNAs sub cell, we design three kinds of anti-reflection coatings and adjust the base region thickness of the GaInNAs sub cell. Developed by a series of experiments, the external quantum efficiency of the GaInNAs sub cell exceeds 80%, and its current density reaches 11.24 mA/cm^2. Therefore the current limit of the 4J solar cell is significantly improved. Moreover, we discuss the difference of test results between 4J and GaInP/GaInAs/Ge solar cells under the 1 sun AM0 spectrum.