Contact Formation on a-Si:H/c-Si Heterostructure Solar Cells

In this chapter a description of the contact formation in a-Si:H/c-Si heterojunction solar cell is detailed. Firstly the doping of amorphous films is reported together with the possibility to enhance the amorphous film conductivity by using Chromium Silicide formation on top of the doped films. Then a finite difference numerical model is used to describe the a-Si:H/c-Si heterojunction solar cell in which both contacts are made by amorphous films. In particular to evaluate the effect of the bandgap mismatch between amorphous and crystalline silicon at the base contact a detailed investigation is presented comparing experimental current voltage characteristics of heterojunction contacts with the results of a simulation based on numerical model. Subsequently, details about formation and properties of a transparent conductive oxide and a screen printing procedure to form metallic grids are presented as a common way to form the heterojunction solar cell electrodes. Finally three examples of heterojunction solar cells are proposed using different approaches to form the contacts. In particular a double side heterojunction cell fabricated on multicrystalline silicon is presented, a laser fired local contact for the rear side of the cell is shown and finally an interdigitated back contact is described. All the investigations are based on our experience on heterostructure solar cells developed in the past years.