Effect of light degradation on bifacial Si solar cells

We fabricated bifacial-type rear-floating-emitter solar cells and triode solar cells from several types of wafers and investigated the light degradation of solar-cell performance. Rear efficiency of a rear-floating-emitter bifacial solar cell degrades in proportion to bulk-minority carrier lifetime. This degradation of cell efficiency is much larger than that reported so far. Bifacial cells must therefore be made from wafers that are not degraded by light. And it was found that magnetic-field-applied CZ wafers or gallium-doped CZ wafers meet this requirement very well. Three-terminal measurement showed that light degradation does not have much influence on rear efficiency of triode cells compared with that of two-terminal bifacial cells.