Highly Stable Micromorph Tandem Solar Cells Fabricated by ECRCVD With Separate Silane Gas Inlets System

In this paper, hydrogenated amorphous silicon (a-Si:H) and microcrystalline silicon (μc-Si:H) films are deposited by electron cyclotron resonance chemical vapor deposition with two separate silane gas inlets. One of the silane gases (S2) is introduced near the substrate region. Effects of S2 flow rate on film properties and solar cell performance are investigated in comparison to traditional plasma-enhanced chemical vapor deposition (PECVD). The results show that the introduction of S2 gas leads to: 1) significant reduction of higher order silane radicals participating film growth; 2) dense film structure with a low microstructure factor of 0.06; and 3) lower surface roughness of the interface between top a-Si:H and bottom μc-Si:H subcells of micromorph tandem cells, favoring bottom μc-Si:H deposition. Single-junction amorphous silicon solar cells show light-induced degradation (LID) of 7.8%, almost half of that observed in PECVD cells. Micromorph tandem solar cells show a 13.3% initial conversion efficiency and a 12.7% stabilized efficiency. Highly stabilized micromorph tandem solar cell with 4.7% LID can be achieved.