Silicon solar thin film spalling using epoxy resin with varying Young’s modulus

Abstract

In a photovoltaic field, a thin film solar cell has benefits on low cost and flexibility. To achieve the thin silicon film without using classical methods which have disadvanges of difficulty, material loss, or expensive process, spalling is introduced in this research. Spalling which applies the fracture phenomenon uses difference of mechanical properties between the substrate and the film deposited on the substrate. By propagating crack with a constant depth, a uniform thin film is achieved by the spalling process. Based on the theoretical model of Z.Suo and J.W. Hutchinson, the depth depends on the spalled Si thickness depends on film/substrate elastic properties(elastic modulus, Poisson’s ratio), and thickness of the film and the substrate. Unlike the usual case which uses metals as materials of stressor layer, the epoxy resins were used in this research. 4 different epoxy resin film were synthesized and analyzed to examine their mechanical properties(the elastic modulus) by nanoindentation. With the DGEBA/MPDA which is one of investigated epoxy resins, the spalling experiment was conducted to exfoliate a thin silicon film from the substrate. Various profiles of the spalled film were achieved and analyzied. The relation of the spalled film and the stressor layer was identified, and compared with analytical calculation from the model of Z.Suo and J.W. Hutchinson. Various surface of the Si film were observed in terms of fracture mechanics. Finally, thin Si films could be obtained with curing epoxy resins. The epoxy resins have advantage on low temperature experiment, and this process is really simple and easy compared with other methods to get the thin silicon film. With more stabilization, the spalling method will be a great technique developing the photovoltaic field.