Characterization of amorphous silicon solar cell preparation processes by real time spectroscopic ellipsometry

Advances in the characterization of amorphous silicon (a-Si:H) solar cell preparation processes using real-time spectroscopic ellipsometry (RTSE) are described. RTSE has been applied to determine critical solar cell properties including the p, i, and n layer thicknesses and their optical bandgaps in the device configuration. First, results for heterojunction solar cells in the SnO₂:F/p-i-n and Cr/n-i-p configurations have been compared. Here, the focus is on the a-Si_1-xC_x:H p layer. The p layer properties determined by RTSE have been related to the open-circuit voltages (V_oc) of co-deposited cells. Second, RTSE has been applied to determine the optical gap profile in alloy-graded a-Si_1-xC_x:H prepared by continuously varying the [CH₄]/{[SiH₄]+[CH₄]} flow ratio. Such graded layers have been incorporated at the p/i interfaces of a-Si_1-xC_x:H solar cells and improvements in V _oc have been obtained