Effects of Surface Conditions of Substrates upon Performance of a-Si Photovoltaic Cells

Abstract
The growth process of a-Si film deposited onto an ITO substrate by a glow discharge reaction in SiH4 was investigated by transmission electron microscopy. The a-Si film grows to form an island structure at the first step (0–200Å-thick) of the growth process. The p-layer of conventional ITO/p-i-n photovoltaic cells has an island structure with a thickness in the range of 50 to 200Å. A multi-junction model in which a-Si photovoltaic cells consist of an ITO/p-i-n junction (hetero-face junction) and an ITO/i-n junction (hetero junction) is proposed. The radius of the island structure in the p-type a-Si is calculated with this model. The result of the calculation is in approximate agreement with that of the observation by transmission electron microscopy. The dependence of the open-circuit voltage of Glass/ITO/p-i-n photovoltaic cells upon the p-layer thickness can be explained by the multi-junction model.

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