Radiation-Hard, High Efficiency InP/InN Tandem Cells

Spire proposes to investigate InP/InN tandem solar cells for applications where extreme radiation-hardness is needed. Indium phosphide (InP) has proven itself as a radiation-hard cell material, and indium nitride (InN) has shown superior radiation resistance to 2MeV protons. InP (1.34 eV) and InN (0.7eV) bandgaps allow current-matching (38 mA/cm2) under the AM0 spectrum, enabling two-terminal operation. We will investigate use of a pseudomorphic InGaP window to boost InP top cell efficiency from its current 19% one-sun AM0 level to 22%. We describe a process that allows the InP top cell to be undisturbed by dislocations from the InN growth. The 0.7eV InN bottom cell has an upper efficiency limit of ~9% AM0; however, the growth of InN would introduce substantial dislocations, and its efficiency would likely be about 4%. However, the dislocations should not compromise the InN radiation hardness, and we believe that the proposed research should lead to tandem space cells with efficiencies of ~26% (1 sun AM0, 25C) which would be flat in power output to fluences beyond 1e16 1MeV electrons/cm2.