Spectroscopic ellipsometry measurements have been performed during the preparation of hydrogenated amorphous silicon p-i-n solar cells in the SnO2:F/p-i-n/Cr configuration. Postdeposition data analysis yields the evolution of bulk, surface roughness, and interface layer thicknesses with ∼0.2 Å sensitivity. In addition, the dielectric functions and optical gaps of the p-, i-, and n-layers are determined in the analysis. With the real time measurement approach, the layer properties are determined in the actual device configuration, rather than being inferred indirectly from studies of thick film counterparts.
We have applied real time spectroscopie ellipsometry (RTSE) to monitor the successive growth of p-type a-Si1-xCx:H and i-type a-Si:H on specular SnO2:F (i.e., the superstrate solar cell configuration) in a single-chamber deposition system. Both the microstructural evolution, which includes the surface roughness and bulk layer thicknesses versus time and bulk layer void volume fraction, as well as the optical properties, which include the dielectric function (1.5–4.0 eV) and optical gap of the individual layers, were determined from RTSE data collected during growth. The accuracy of our approach is demonstrated by correlating structural parameters obtained both by RTSE and atomic force microscopy. Based on prior information deduced by RTSE, the TCO/p/i structure was fabricated with optimized procedures that have sought to minimize TCO/'p and p/i interfacial problems. These studies illustrate that RTSE can be a valuable tool for identifying problems in the fabrication of a-Si:H solar cells and ultimately improving cell performance.
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