Quadruple-Junction Thin-Film Silicon Solar Cells Using Four Different Absorber Materials

We fabricated and studied quadruple-junction wide-gap a-Si:H/narrow-gap a-Si:H/a-SiGex:H/nc-Si:H thin-film silicon solar cells. It is among the first attempts in thin-film photovoltaics to make a two-terminal solar cell with four different absorber materials. Several tunnel recombination junctions were tested, and the n-SiOx:H/p-SiOx:H structure was proven to be a generic solution for the three pairs of neighboring subcells. The proposed combination of absorbers led to a more reasonable spectral utilization than the counterpart containing two nc-Si:H subcells. Besides, the use of high-mobility transparent conductive oxide and modulated surface texture significantly enhances the total light absorption in the absorber layers. This work paved the way toward high-efficiency quadruple-junction cells, and a practical estimation of the achievable efficiency was given.