Cheaper and more flexible multiple thin crystalline silicon wafers

Researchers have found a way to make the manufacture of crystalline silicon materials faster and more affordable. The technology enables a large number of crystalline layers, controlled for thickness, to be produced from a single crystalline silicon wafer in just a single step. The outcome is a kind of crystalline silicon ‘millefeuille’ produced more efficiently, more rapidly and more affordably than by existing methods.

The methodology developed by the scientists from the Nanoengineering Research Centre (CRnE) and the Department of Electronic Engineering at the Universitat Politècnica de Catalunya BarcelonaTech (UPC) is based on making small pores in the material and applying a high temperature during the manufacturing process.

Multiple separate crystalline silicon wafers are obtained by carefully controlling the pore profiles. Precise control over diameter controls both the number of layers and their thickness. The millefeuille silicon layers are then separated by exfoliation. The resulting number of silicon layers is determined by the thickness of the layers themselves and the initial thickness of the wafer. The CRnE researchers have succeeded in creating up to 10 thin wafers (5-7 mm thick) from a single 300 mm thick wafer. Silicon wafers have potential photovoltaic applications in the medium term in the conversion of sunlight to electricity and the production of more affordable, more flexible and lighter solar cells.

The demand for thin and ultrathin crystalline silicon wafers responds to the application possibilities offered by 3D circuit integration of microelectromechanical systems (MEMS) with conventional microchips and also to the latest generation of photovoltaic technology. Wafer cutting for solar cell production, for example, has been steadily improving. Thickness has been reduced (350 mm in the 1990s to 180 mm currently) while efficiency has been enhanced, resulting in reduced manufacturing costs; nonetheless, greater reductions are likely to be difficult to achieve. It has been shown that, despite lesser thickness, the wafers retain a high capacity to absorb solar energy and convert it into electricity.

The results of the research, conducted by David Hernández, Trifon Trifonov and Moisés Garín, led by Professor Ramon Alcubilla, have recently been published in the online version of the landmark journal Applied Physics Letters.