Microcrystalline silicon solar cells deposited at high rates

Hydrogenated microcrystalline silicon (mu c-Si:H) thin-film solar cells were prepared at high rates by very high frequency plasma-enhanced chemical vapor deposition under high working pressure. The influence of deposition parameters on the deposition rate (R-D) and the solar cell performance were comprehensively studied in this paper, as well as the structural, optical, and electrical properties of the resulting solar cells. Reactor-geometry adjustment was done to achieve a stable and homogeneous discharge under high pressure. Optimum solar cells are always found close to the transition from microcrystalline to amorphous growth, with a crystallinity of about 60%. At constant silane concentration, an increase in the discharge power did hardly increase the deposition rate, but did increase the crystallinity of the solar cells. This results in a shift of the mu c-Si:H/a-Si:H transition to higher silane concentration, and therefore leads to a higher R-D for the optimum cells. On the other hand, an increase in the total flow rate at constant silane concentration did lead to a higher R-D, but lower crystallinity. With this shift of the mu c-Si:H/a-Si:H transition at higher flow rates, the R-D for the optimum cells decreased. A remarkable structure development along the growth axis was found in the solar cells deposited at high rates by a "depth profile" method, but this does not cause a deterioration of the solar cell performance apart from a poorer blue-light response. As a result, a mu c-Si:H single-junction p-i-n solar cell with a high efficiency of 9.8% was deposited at a R-D of 1.1 nm/s. (C) 2005 American Institute of Physics.