1. Technical Field
The present invention relates to solar cells, and more particularly to devices and methods which employ a single chamber process for fabricating photovoltaic devices.
2. Description of the Related Art
Fabrication of amorphous hydrogenated silicon (a-Si:H) solar cells is performed in a multi-chamber cluster tool. Constituent active layers in such devices include a p-type layer (or p-layer), an intrinsic layer (or i-layer) and an n-type layer (or n-layer), collectively a p-i-n or pin stack. The p, i and n (e.g., a-Si:H) layers are deposited in separate chambers, which results in reduced manufacturing efficiency.
In some processes, a same chamber is reconfigured for the deposition of each new layer. Solar cell fabrication using the single chamber suffers from drawbacks. For example, when diborane is used for a p-type dopant source (e.g., boron), boron is left over in the chamber. This results in a higher probability of the p-i interface being contaminated, resulting in poor device performance.
In another example, when trimethylborane (TMB) is used for a p-type dopant source, less boron is left over. However, for materials, e.g., a-Ge:H, a-Si:H, etc., it is extremely difficult to provide boron to these films without contaminating reactants being present (the process is not flexible for all device materials). TMB is also an order of magnitude more expensive than diborane doping, and unintentional carbon doping often occurs resulting in poor doping activation.