Mews, M.; Schulze, T.F.; Mingirulli, N.; Korte, L.: Amorphous silicon passivation of surfaces promoting epitaxy. Energy Procedia 38 (2013), p. 855-861
Open Accesn Version
A two-step approach to passivation of crystalline silicon (c-Si) by hydrogenated amorphous silicon (a-Si:H) for amorphous/crystalline silicon (a-Si:H/c-Si) heterojunction solar cells is discussed: The combination of low temperature a-Si:H deposition of ultrathin (~7 nm) (i)a-Si:H and hydrogen plasma post deposition treatments is shown to yield charge carrier lifetimes of 8 ms on c-Si<100>, i.e. a crystal surface which can be difficult to passivate because it promotes epitaxial growth. It is shown that the passivation improvement upon hydrogen plasma treatment (HPT) stems from diffusion of hydrogen atoms to the heterointerface and subsequent dangling bond passivation. Upon HPT, the a-Si:H hydrogen density increases, leading to a valence band offset increase at the heterojunction. However, the film disorder is not increased. Thus, HPT allow for a-Si:H band gap and a-Si:H/c-Si band offset engineering. Furthermore hydrogen plasma treatments enable the application of a-Si:H/c-Si-heterojunction solar cells concepts on surfaces that promote epitaxy, like Si<100> and (nano)structured surfaces.