Longpass Distributed Bragg Reflector for Improved Radiation Tolerance and Current Matching in Multijunction Solar Cells

Reducing the thickness of the GaAs absorber in a multijunction solar cell can increase radiation tolerance, while incorporation of a distributed Bragg reflector (DBR) can maintain current density by maintaining optical path length. In a closely current matched multijunction design, low energy sidelobe reflections of the DBR parasitically affect the subcell below the GaAs junction. A variation of the DBR design is proposed to mitigate this loss mechanism by maximizing transmission below the main Bragg peak. Through simulated multijunction and experimental verification of test structures, this paper will show how this “longpass” DBR can be optimized to improve current matching while maintaining radiation hardening afforded by thinning the GaAs junction.