A direct correlation between film structure and solar cell efficiency for HWCVD amorphous silicon germanium alloys |
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Authors: | AH Mahan Y Xu DL Williamson |
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Affiliation: | a NREL, 1617 Cole Boulevard, Golden, CO 80401, United States b Physics Department, Colorado School of Mines, Golden, CO 80401, United States |
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Abstract: | The film structure and H bonding of high deposition rate a-SiGe:H i-layers, deposited by HWCVD and containing ~ 40 at.% Ge, have been investigated using deposition conditions which replicate those used in n-i-p solar cell devices. Increasing the germane source gas depletion in HWCVD causes not only a decrease in solar cell efficiency from 8.64% to less than 7.0%, but also an increase in both the i-layer H preferential attachment ratio (PA) and the film microstructure fraction (R?). Measurements of the XRD medium range order over a wide range of germane depletion indicate that this order is already optimum for the HWCVD i-layers, suggesting that energetic bombardment of a-SiGe:H films may not always be necessary to achieve well ordered films. Preliminary structural comparisons are also made between HWCVD and PECVD device layers. |
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Keywords: | Amorphous silicon germanium Hot wire CVD H bonding Solar cells |
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