Optimization of protocrystalline silicon p-type layers for amorphous silicon n-i-p solar cells

Real time spectroscopic ellipsometry has been applied to develop deposition phase diagrams for p-type hydrogenated silicon (Si:H) films prepared at low temperature (200degreesC) by rf plasma-enhanced chemical vapor deposition using gas mixtures of SiH4, H-2, and BF3. These diagrams depict the regimes of accumulated thickness and H-2-dilution ratio R = [H-2]/[SiH4] within which p-type amorphous Si:H [a-Si:H], mixed-phase Si:H [(a+ muc)-Si:H], and single-phase microcrystalline Si:H [muc-Si:H] films are obtained in depositions on R = 0 a-Si:H surfaces. The performance of n-i-p solar cells incorporating p-layers deposited under the same conditions as those used in the phase diagram development has been correlated with the deduced p-layer characteristics. This correlation demonstrates that V., is maximized when the highest possible R value is used for the p-layer while ensuring single-phase amorphous film growth throughout its thickness. (C) 2004 Elsevier B.V. All rights reserved.