Argon dilution of silane as an alternative to hydrogen dilution for stable and high efficiency silicon thin films solar cells

Deposition of hydrogenated amorphous silicon (a-Si:H) thin films by rf-PECVD from a silane highly diluted into hydrogen mixture was shown to give more stable layers and solar devices. However, hydrogen-silane mixture is quite hazardous. That is why the possibility to obtain stable and device grade thin films using argon dilution of silane has been investigated. We present the correlations we found between transport, structural and deposition plasma properties of a-Si:H films prepared from silane-argon mixtures, these correlations leading to the choice of optimum deposition parameters resulted in device grade silicon thin films. We also present the results obtained on a large set (75 nos.) of I cm(2) p-i-n diodes for which all the layers were deposited under argon dilution including the p and n layers. A mean conversion efficiency of 6.5% was reached, the best devices exhibiting conversion efficiency of 8%. The light degradation is smaller than with diodes prepared with conventional a-Si:H and the best diodes present a 7% stabilized efficiency after 100 h under AM 1.5 illumination. We conclude that argon dilution of silane can be an alternative to the hydrogen dilution to prepare high conversion efficiency and stable devices by rf-PECVD with the major asset of a less hazardous process. (C) 2004 Elsevier B.V. All rights reserved.