High Efficiency and High Rate Deposited Amorphous Silicon-Based Solar Cells

Triple-junction a-Si based solar cells, having a structure ofSS/Ag/ZnO/n/n/b/a-SiGe-i/b/p/p/n/n/b/a-SiGe-i/b/p/p/n/n/a-Si-i/p/p/ITO, are fabricated at the University of Toledousing a multi-chamber, load-locked PECVD system. We studied the effect of heavily doped pand n layers deposited at the tunnel junction interfaces between the top and middle componentcells and between the middle and bottom component cells on the efficiency of triple-junctionsolar cells. Preliminary results show that thin, ~ 1nm, interfacep/n layers improve the solar cellefficiency while thicker interface layers, ~4nm thick, cause the efficiency to decrease.Incorporating the improved interface layers at the tunnel junctions, as well as earlierimprovements in the intrinsic layers, the p-i interface in terms of reducing the band-edge offset,and the a-SiGe component cells using bandgap-graded buffer layers, we fabricated triple-junction solar cells with 12.71% efficiency in the initial state and 10.7% stable efficiency after1000 hours of 1-sun light soaking. Samples sent to NREL for independent measurements show11.8% total-area (or 12.5% active-area) initial efficiency.