a-Si:H/a-Si:H stacked cell with 9% stabilised efficiency
deposited in a single-chamber reactor at high rate due to VHF-GD
R. Platz, D. Fischer, S. Dubail and A. Shah
Institut de Microtechnique, Université de Neuchâtel, Rue A.-L. Breguet 2, CH-2000 Neuchâtel
Tel.: +41-32-718 33 53 Fax: +41-32-718 32 01 E-Mail: firstname.lastname@example.org
In the present paper the authors present results on a-Si:H/a-Si:H stacked cells deposited in a single-chamber
reactor by the very high frequency - glow discharge (VHF-GD) deposition technique at 70 MHz. Hydrogen
dilution of the i-layer yields more stable amorphous p-i-n solar cells, similar to what is observed for RF
deposition at 13.56 MHz plasma excitation frequency. Regarding the stacked cell design, the authors show by
experiment and simulation that it is important to carefully adjust the current mismatch between the component
cells such as to obtain a slight top-cell-limited behaviour after degradation. The authors present an a-Si:H/a-
Si:H stacked cell with an initial efficiency of 9.8 % showing only 8 % relative degradation; this results in a
stabilised efficiency of 9 % as confirmed by an independent laboratory. The deposition rate of the employed
H2-diluted i-layer material is 4 Å/s. It is therefore demonstrated that it is possible to make highly efficient
stacked cells showing good stability also in a single-chamber system and employing the VHF technique to
obtain higher rates.
Keywords: stability - 1: stacked solar cells - 2: rapid growth - 3.
The VHF deposition technique at 70 MHz has shown to
yield much higher growth rates than those obtained for
"standard" 13.56 MHz plasma deposition ; this becomes
even more important in the case of H2-dilution (as used to
obtain i-layers with higher stability), where deposition rates
generally strongly decrease. However, the question
persisted as to whether cells obtained from VHF deposition
at higher growth rates would be as stable as "slowly"
grown cells from "conventional"