a-Si:H/a-Si:H stacked cell from VHF-deposition in a single chamber reactor with 9% stabilized efficiency R. Platz, D. Fischer, S. Dubail and A. Shah Institut de Microtechnique, Université de Neuchâtel Rue A.-L. Breguet 2, CH-2000 Neuchâtel Abstract In the present paper we 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. High dilution ratios of the i-layer are found to enhance contaminations. This is, for the single chamber reactor, due to the etching effect of the highly reactive H 2 -plasma. Additionally, oxygen incorporation into the i-layer is favored by the high hydrogen dilution. Different means to suppress these contaminations are employed and discussed. Regarding the stacked cell design, we 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 behavior after degradation. We present an a-Si:H/a-Si:H stacked cell with an initial efficiency of 9.8 % showing only 8 % relative degradation which results in a stabilized efficiency of 9 %. The deposition rate of the employed H 2 -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. Introduction Very encouraging results for stabilized solar cell efficiencies have been achieved at different laboratories, all of them using multichamber reactors for the deposition of a-Si:H based solar cells: triple junction: USSC 11.8% [1]; double junction: Sanyo 10.6% [2], Solarex 9.6% [3], Fuji 10% [4], PST 6.3% for a 0.6 m 2 commercial module [5], Research Center Jülich 9.2% [6]). In References [1-3], a-SiGe:H alloys are employed for the middle and/or bottom cells, references [4-6] do not use a-SiGe:H alloys. Today, most solar cells are deposited in a multichamber reactor, at least in the case of industrial production. However, still a number of industries (e.g. NAPS France [7], APS [8], Solems [9]) deposit cells in a single chamber system, as such a system can be an economically interesting alternative to expensive multichamber systems. When employing hydrogen (H 2 ) dilution for the deposition of more stable i-layers [10], contamination of the i-layer with oxygen, but also boron and phosphorus, can become a major problem. Oxygen contamination is probably to some extent a problem for all deposition systems whereas cross-contaminations of the dopant gases may not play such an important role in the case of multichamber systems. The VHF deposition technique at 70 MHz has shown to yield much higher growth rates than for "standard" 13.56 MHz deposition [11], which becomes even more interesting in the case of H 2 -dilution of the i-layer where deposition rates generally strongly decrease. However, there have still been questions persisting whether cells obtained from VHF deposition at higher growth rates would be less stable than Published in Solar energy materials and solar cells 47, issue 2, 157-172, 1997 which should be used for any reference to this work 1