Annealing of defect sites in radiation damaged indium phosphide solar cells through laser illumination

Abstract

This thesis reports the results of a laser annealing technique used to remove defect sites from radiation damaged indium phosphide diffused junction solar cells. This involves the illumination of damaged solar cells with a continuous wave laser to produce a moderate heating and a large forward-biased current. The InP cells were irradiated with 27 MeV electrons to a given fluence, and tested for degradation. Light from an argon laser was used to illuminate each cell with an irradiance of 2.5 W/sq cm, producing a current density 7 to 10 times larger than under AMO conditions. Cells were annealed at 48.5 deg C, 60 deg C, and 75 deg C for periods of 15 to 60 minutes, and cooled to 25 deg C for power recovery determination. Annealing at 48.5 deg C resulted in a recovery of 17 to 18% of the power lost due to irradiation, and annealing cells at 60 deg C produced a recovery of 43 to 48%. A single test of the technique at 75 deg C produced a net recovery of only 21% of the power lost. These results indicate that significant power recovery results from the annealing of defects within InP solar cells. Continuing research should involve the repeating of the test at 75 deg C, and irradiations with electrons or protons of energies expected in the space environment.