35th EU PVSEC, 24 - 28 September 2018
SQUARE - Brussels Meeting Centre, Brussels, Belgium

30 January 2017

Kerf-less Wafers – Start-Ups Working On True Revolution For Crystalline Silicon Solar Wafer Manufacturing

Reducing silicon consumption has always been the focus of PV manufacturers – and it still makes a lot of sense. Though silicon is not expensive these days, this core material for most cells is still a significant contributor to module costs - with a share of over 20% for the cost leaders. One way to reduce silicon usage per cell is to decrease the thickness of the wafer. An even more interesting option is to reduce the so-called kerf. As much as close to 50% of the silicon is lost as waste (kerf) during the ingot sawing process to produce wafers. While reducing kerf losses is on the agenda of wafer makers, some companies, especially start-ups, are trying to eliminate kerf losses completely. Their kerf-less solutions not only dramatically save on silicon raw material, if it worked in large-scale manufacturing, it could revolutionize today’s value chain for crystalline silicon modules by eradicating the upstream production processes of ingot growing and wafering, but depending on the process, even polysilicon production. According to one company active in that field, NexWafe, their technology could save up to 60% of silicon lost during sawing, reduce energy consumption during manufacturing by up to 80%, and require 70% less investment cost for its scrap-free wafer production.

 

nextwafe

Photo Credit: NexWafe

NexWafe: Epitaxially grown wafers on reusable substrates

NexWafe, a spin-off of renowned German Fraunhofer Institute of Solar Energy Systems (ISE), is one of the promising start-ups in the field of kerf-less wafers. In its approach, a thick crystalline silicon layer is epitaxially deposited on a reusable template using Trichlorosilane (TCS) as a gaseous precursor. Then the fully grown wafer is detached from the seed wafer. NexWafe is aiming to produce wafers of standard thickness, 150 to 180µm. This means, they are a drop-in replacement for traditional CZ wafers. As a first step, NexWafe is aiming at the n-type wafer segment. The n-type wafers produced from the epi-process show average minority carrier lifetimes above 1000 μs, indicating the same quality as n-type CZ wafers. Small solar cells of 2 x 2 cm made out of these wafers reached 20% efficiency. These results were presented at the 31st EU PVSEC conference in Hamburg in 2015. While ISE provided the seed funds, NexWafe was able to secure €6 million in Series A financing from private equity firm Lynwood (Schweiz) AG in March 2016. Only very recently, in December 2016, NexWafe was selected one of the top award winners of the European Venture Contest.

Crystal Solar: From Gas to Wafer with Built-in Junction

Crystal Solar is working on a similar approach, which it calls “Direct Gas to Wafer”. But the US-based startup takes a slightly different path when it comes to the final product. Since the epitaxial process enables to induce the junction as part of the growth process, Crystal Solar is planning to supply such semi-processed wafers with built-in junction. Crystal Solar is working on both n-type and p-type wafers.The technology was selected in the prestigious SunShot Initiative’s Photovoltaic PV Incubator Program of the US Department of Energy (DOE) in 2011. Crystal Solar has been also cooperating with Belgium-headquartered research institute IMEC for cell processing. At the 32nd EU PVSEC conference in Munich in 2016, IMEC presented the results of its n-PERT cell process adapted to Crystal Solar’s n-type wafers with built-in rear p+ emitter – an efficiency of 22.5% for a substrate area of 238.9 cm2. The cell has an open circuit voltage of about 700 mV, which indicates a better quality of Crystal Solar’s wafer compared to standard products. In September 2016, Crystal Solar was awarded a $3 million cooperative agreement by the DOE’s SunShot Initiative to develop high efficiency epitaxial solar cells and demonstrate commercial level yields at its pilot production facility in the US.

1366: First Commercial Kerf-less Wafers in Sight

1366 Technologies is yet another kerf-less wafer technology pursuant – and again the technology of this most advanced startup in this segment is slightly different. First of all, 1366 is planning to produce multicrystalline silicon substrates directly from silicon melt. That means the technology relies on standard polysilicon as feedstock for its process – and explains why 1366 cooperates with a silicon manufacturer, Wacker Chemie from Germany, which even invested in the US start-up. The company has first reported about its technology at a EU PVSEC event a while ago – at the 27th edition in 2012, the inventor of the technology, MIT professor and 1366 CTO Elly Sachs presented a paper about “High Performance 156 mm Silicon Wafers At Half the Cost of Sawn,” demonstrating that the Direct Wafer process leads to wafers directly from the melt.

Since then 1366 has made considerable progress. Take, for example, the so-called 3D wafer technology. As presented at the 32nd EU PVSEC conference in Munich last June, it is all about making wafers with a thin bulk and a thick edge part, which better protects the silicon slices from breakage. The inherent ability of 1366’s process working at the melt level enables controlling the wafer thickness locally, resulting in 3D wafers. 1366 emphasized that its “solution can be delivered at a cost below <$0.40/wafer and silicon usage below 1.5 g/W." As for the cell processing side, 1366 is cooperating with Hanwha Q CELLS’ R&D team in Germany. The partnership has resulted in a considerable efficiency boost. Very recently, in December, Hanwha Q CELLS reached a 19.6% efficiency for PERC cells using 1366’s wafers. That’s close to 2% absolute gain in efficiency since the beginning of the strategic collaboration in March 2015. Now the solar community is waiting for commercial production to start, because unlike NexWafe and Crystal Solar, 1366 has already secured significant funds from investors in several financing rounds, a $150 million loan guarantee and access to an incentive package of up to $56 million from New York State for its first factory.

We are looking forward to discussing innovate PV technologies, such as kerf-less wafering, at the upcoming 33rd EU PVSEC in Amsterdam, The Netherlands from 25 - 29 September 2017. If you are working in the solar research field, please participate in our Call for Papers and provide us with your abstract by 10 February 2017.