Cheaper solar cells through kerfless wafers

April 18, 2016 // By Graham Prophet
With the use of kerfless epitaxial wafers, the Belgian research organisation Imec together with Calfornia-based Crystal Solar say that they potentially have a disruptive solution for the solar cell industry, substantially reducing the cost of Si solar cells.

Crystal Solar is a pioneer in direct wafer growing technologies for the next generation of solar photovoltaic products. With nanotechnology body imec, the collaboration has announced that they have achieved a 22.5% cell efficiency (certified by FhG ISE CalLab) with nPERT (n-type passivated emitter, rear totally-diffused) silicon (Si) solar cells manufactured on 6-inch (150 mm) mono-crystalline epitaxially grown kerfless wafers.

[Editor's note; the term kerf denotes the width of a saw blade or the cut it makes in a workpiece. Conventional manufacture of silicon involves first growing a single-crystal ingot, then sawing it (by steel or diamond-coated wire) into wafers. This is energy-intensive and wasteful of material; even best practice loses nearly half of the grown silicon to the saw cuts. Many efforts have been made, and venture capital invested (and lost) to produce wafers with equivalent quality of monocrystaline lattice structure by some form of alternative process – direct production of the wafer, in effect. Such wafers would avoid the losses to sawing, hence; kerfless.]

Claiming an industry first, imec and Crystal Solar have demonstrated the highest efficiency to-date for homojunction solar cells on epitaxially grown silicon wafers, paving the way toward industrialization of this promising technology.

Crystal Solar’s manufacturing technology called Direct Gas to Wafer enables direct conversion of feedstock gas to mono crystalline silicon wafers by high throughput epitaxial growth. By skipping the polysilicon, ingoting and the wire-sawing steps altogether, this approach not only results in lowest cost/Watt for the wafers but also significantly reduces the capital required to set up a manufacturing plant. Furthermore, this process enables the growth of high quality p-n junctions in-situ which reduces cell making steps while increasing the efficiency.