High Efficiency Quantum Dot Molecule Solar Cells for High Concentration Sunlight Application

InAs quantum dot molecule (QDM) solar cells are fabricated by modified molecular beam epitaxy technique. With multi-stacks and high dot density greater than 10¹² cm^-2, a QDM solar cell with hetero-structure provides high conversion efficiency of 25.9 % under 100 mW/cm² AMI solar simulator. The improved efficiency of this novel nanostructure solar cell is due to the extension of solar response to long wavelength region beyond the band edge of GaAs, which is used as the substrate for the hetero-structure of AlGaAs/GaAs having InAs quantum dot molecules as the active part of the solar cells. It is also found that QDM solar cells perform better at high concentration sunlight due to the low dimensionality of quantum dot structure.