Radiation damage and defect behavior in ion-implanted, lithium counterdoped silicon solar cells

Boron-doped silicon n+p solar cells were counterdoped with lithium by ion implantation and the resultant n+p cells irradiated by 1 MeV electrons. Performance parameters were determined as a function of fluence and a Deep Level Transient Spectroscopy (DLTS) study was conducted in order to correlate defect behavior with cell performance. It was found that the lithium counterdoped cells exhibited significantly increased radiation resistance when compared to boron doped control cells. Isochronal annealing studies of cell performance indicate that significant annealing occurs at 1000C. Isochronal annealing of the deep level defects showed a correlation between a single defect at E /sub v+/ .43 eV and the annealing behavior of short circuit current in the counterdoped cells. It was concluded that the annealing behavior was controlled by dissociation and recombination of this defect. The DLTS studies also showed that counterdoping with lithium eliminated at least three deep level defects and resulted in three new defects. It was speculated that the increased radiation resistance of the counterdoped cells is due primarily to the interaction of lithium with oxygen, single vacancies and divacancies and that the lithium-oxygen interaction is the most effective in contributing to the increased radiation resistance