| Person in charge of the project: |
Low-cost Si solar cells based on stress-induced layer transfer|
Today, the cost of standard silicon solar cells is still too high for general application. The main reason for this is that solar cells are made with rather thick wafers of high purity silicon. In order to reduce, the industry is moving to thinner and thinner wafers. Nevertheless, conventional wire-sawing consumes at least 300 µm for one wafer (including kerf loss), and cannot produce wafers thinner than 140 µm.
Recently, IMEC has introduced a completely new wafering method for the production of ~50-µm-thick crystalline silicon wafers. It is a lift-off process that requires only simple equipment. On a thick substrate a layer is deposited with mismatched thermal expansion coefficient with respect to the substrate (for instance a metal layer). Upon cooling, the differential contraction induces a large stress field which is released by the initiation and the propagation of a crack parallel to the surface. Films with an area of 25 cm2 and a thickness of 30-50 µm have been obtained.
The topic of this PhD is to investigate this technique, understand the process and to control the stress-induced spalling process. The purpose is to lift-off multiple layers from the same wafers, leading to a very low Si consumption per solar cell. This involves both experimental work and simulation. Handling issues and wafer breakage also need to be looked at, as well as the processing of these thin silicon foils into efficient solar cells.
Faculty of Engineering
Doctoral Programme in Engineering
Duration of the project:
01.10.2008 - 01.10.2012