A-SI-H A-SI-H STACKED CELL FROM VHF-DEPOSITION IN A SINGLE CHAMBER REACTOR WITH 9-PERCENT STABILIZED EFFICIENCY/

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-cha mber reactor, due to the etching effect of the highly reactive H-2-pla sma. Additionally, oxygen incorporation into the i-layer is favored by the high hydrogen dilution. Different means to suppress these contami nations are employed and discussed. Regarding the stacked cell design, we show by experiment and simulation that it is important to carefull y adjust the current mismatch between the component cells such as to o btain 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% show ing only 8% relative degradation which results in a stabilized efficie ncy of 9%. The deposition rate of the employed H-2-diluted i-layer mat erial is 4 Angstrom/s. It is therefore demonstrated that it is possibl e to make highly efficient stacked cells showing good stability also i n a single-chamber system and employing the VHF technique to obtain hi gher rates.