Super-Multi-Junction Solar Cell, Device Configuration with the Potential of More Than 50 % of the Annual Energy Conversion Efficiency (Non-Concentration)

Abstract

The highest efficiency solar cell won in the efficiency race does not always give the most excellent annual energy yield in the real world solar condition that the spectrum is ever-changing. The study of the radiative coupling of the concentrator solar cells implied that the efficiency could increase by the recycle of the radiative recombination generated by the surplus current in upper junction. Such configuration of the multi-junction cells is often called by a super-multi-junction cell. We expanded it to non-concentrating installation. It was shown that this super-multi-junction cell configuration was found robust and can keep almost the same to the maximum potential efficiency (50 % in realistic spectrum fluctuation) up to 10 junctions by a Monte Carlo method. The super-multi-junction cell is also robust of the bandgap engineering of each junction. Therefore, the future multi-junction may not be needed to tune the bandgap for matching the standard solar spectrum, as well as relying upon artificial technologies like ELO, wafer-bonding, mechanical-stacking, and reverse-growth, but merely uses up-right and lattice-matching growth technologies. Although we have two challenging techniques; one is the optical cap layer that may be the directional photon coupling layer in the application of the photonics technologies, and another is the high-quality epitaxial growth with almost 100 % of the radiative efficiency.