Physics of quantum well solar cells

Incorporating quantum wells into multi-junction III-V solar cells provides a means of adjusting the absorption edge of the component junctions. Further, by using alternating compressive and tensile materials, a strain-balanced stack of quantum well and barrier layers can be grown, defect free, providing absorption-edge / lattice parameter combinations that are inaccessible using bulk materials. Incomplete absorption in the quantum wells has been addressed using a distributed Bragg reflector, extending the optical path length through the cell and enabling photon recycling to take place. State of the art single-junction quantum well solar cells have now reached an efficiency of 27.3% under 500X solar concentration and are projected to reach 34% in a double junction configuration.