Thermal annealing of proton-irradiated silicon solar cells

Solar cells made from 1.5- and 10-Ωċcm p-type silicon, with silver-titanium evaporated electrodes, were irradiated by 4.6-MeV protons at room temperature to fluences ranging from 1 × 10¹⁰to 1 × 10¹²protons/cm². The photovoltaic current-voltage characteristics, the photovoltaic spectral response, and the minority carrier diffusion length were studied as the solar cells were annealed isochronally to temperatures up to 600°C. The proton radiation damage annealed in two stages, the first occurring between 50° and 150°C, and the second between 350° and 450°C. The removal of proton damage in this manner differs markedly from the annealing reported for 1-MeV electron damage, where practically no recovery of the photovoltaic properties is observed below 350°C. At any selected annealing temperature, the 10-Ω ċ cm cells were observed to recover to a slightly greater degree than the 1.5-Ω ċ cm type.