Some observations on seeding and stability of nc-Si solar cells

We describe a study on the critical seeding step for preparation of nanocrystalline silicon (nc-Si) p-i-n type solar cells by single-chamber RF-PECVD on native SnO₂ coated glass superstates. A novel seeding scheme using closed-chamber (CC) plasma has proved effective in eliminating the Si:H incubation layer and reduce optical loss without using ZnO coating. This seeding process does not accumulate a film. Rather, it modifies the surface region of a pre-deposited film. The efficacy of this approach is, however, hindered both by dopant cross-contamination and process sensitivity to the degree of substrate texture. This method is compared with conventional p-layer seeding using non-static plasma which, on ZnO-coated SnO₂, has resulted in 6.5% single cells with ZnO/AI back contact. Also compared is i-layer seeding. Our ´near-the-edge´ nc-Si single junction cells show excellent stability under light and in the dark, without post-deposition oxidation. An 8.7% a-Si/nc-Si tandem solar cell (post light soaking) has been confirmed by NREL.