Annealing and anomalous high-energy electron irradiation effects in low-cost silicon N+P solar cells

Publisher Website
Google Scholar
Abstract
Silicon solar cells of N+P type made from multiple ingots grown from a single crucible were either subjected to 1‐MeV electron irradiation (fluence up to 1016 electrons/cm2) and then annealed at 450 °C for 20 min or to the annealing alone with no electron irradiation. Electron irradiation gave the expected degradation of longer‐wavelength cell response but at shorter wavelengths produced a marked enhancement of response with peak change of some 40% at 0.44 μm. Subsequent thermal anneal at 450 °C reduced the long‐wavelength degradation, but the enhancement at shorter wavelengths persisted. Excitation at the shorter wavelength is predominantly in the N+‐diffused layer and to some extent in the junction region of the cell. Anneal of unirradiated cells at 450 °C also produced the shorter‐wavelength enhancement at about half of that due to electron irradiation and more enhancement into the longer wavelength region (up to 0.8 μm), finally giving a small degradation. These effects in the different cell regions are attributed to a decrease in interstitial oxygen‐impurity complexes which act as deep recombination levels and the formation of substitutional oxygen‐silicon vacancy centers which act as donors. The investigations indicate that thermal regimes during cell processing can produce cell spectral characteristics that might be further improved by modification of such regimes.