Incorporation of Photonic Structures for Improved Radiation Tolerance of Lattice Matched Triple Junction Solar Cells

A method of improving the radiation tolerance of a triple junction solar cell, lattice matched to germanium, by thinning the GaAs middle junction and maintaining power conversion efficiency through the use of a distributed Bragg reflector and patterned dielectric diffraction grating is discussed. Simulations using Sentaurus RSoft show that current density lost through reduction of the GaAs base thickness can be recovered by increasing the optical path length through the device using photonic structures such as a distributed Bragg reflector (DBR) and patterned dielectric gratings. In this paper, the simulation is further compared to experiment focusing on the GaAs middle cell, where prior to growing the diode a conductive DBR is grown epitaxially using MOCVD. Internal and external quantum efficiency, as well as performance under 1-sun illumination, is presented showing nearly complete recovery of performance to optically-thick conditions, while using half the thickness of GaAs absorber.