High End-of-life Power Density InP-on-Ge Solar Cells

InP SOLAR CELLS POSSESS UNIQUE INTRINSIC RADIATION HARDNESS AND SELFRECOVERY MECHANISMS WHICH MAKE THEM AN ENABLING TECHNOLOGY, ALLOWING MISSIONS IN HIGH-RADIATION ORBITS IN THE VAN ALLEN BELTS PREVIOUSLY AVOIDED WITH GaAs AND Si CELL TECHNOLOGIES. ONE-SUN InP CELLS EXCEEDING 19% EFFICIENCY AT AMO (A WORLD RECORD) HAVE BEEN BUILT AT SPIRE; EVEN GREATER EFFICIENCY COULD BE OBTAINED WITH InP CONCENTRATOR CELLS. HOWEVER, InP CELL USE HAS BEEN LIMITED BY THE COST AND FRAGILITY OF THE InP SUBSTRATES, WHICH REQUIRES USING THICKER AND HEAVIER SUBSTRATES, ADDING TO THE LAUNCH WEIGHT. SPIRE PROPOSES TO OVERCOME THESE LIMITATIONS BY EXPLORING THE PERFORMANCE OF InP CELLS ON Ge WAFERS, A CELL TYPE NEVER BEFORE INVESTIGATED. Ge WAFERS ARE LESS THAN 1/10TH THE COST OF InP IN LARGE QUANTITIES. THEY ARE MUCH STRONGER THAN InP WAFERS, SO MUCH THINNER AND LIGHTER SUBSTRATES CAN BE USED. IN HIGH RADIATION ORBITS EQUIVALENT TO FLUENCES OF 10 (17) 1 MeV ELECTRONS/CM2, WE PREDICT A 15% BEGINNING-OF-LIFE (BOL) InP-ON-Ge CELL WILL HAVE UP TO 20% HIGHER END-OF-LIFE (EOL) POWER DENSITY THAN A 19% BOL InP-ON-InP CELL, DUE TO ITS LIGHTER, LOWER COST Ge WAFER, AND MAY HAVE UP TO 250% HIGHER EOL THAN A 14% BOL Si CELL, DUE TO THE HIGHER InP EOL EFFICIENCY.