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EU consortium cuts photovoltaic production times in half A
research project led by the Fraunhofer Institute for Solar Energy Systems (ISE) has
developed a proof of concept for a silicon solar cell production line with a throughput of 15,000 to 20,000 wafers per hour. This represents double the usual
throughput and is due to improvements to several individual process steps. The concept was presented at the World Conference on Photovoltaic Energy Conversion in Milan at the end of September. The research project is being funded by
the Federal Ministry for Economic Affairs and Climate Action and involves plant manufacturers, metrology companies and research institutions.
‘In 2021, 78 per cent of all silicon solar
cells were produced in China,’ says Ralf Preu, Division Director of PV Production Technology at Fraunhofer ISE. ‘In order to deploy more solar installations as quickly as possible and to make our supply chains more robust, Europe should re-establish its own production centres for high-efficiency solar cells.’
New concepts for silicon solar cell production The consortium investigated every stage of the production of high-efficiency silicon solar cells to optimise the entire process. Several process steps required new developments.
Experimental wafer stack design for diffusion in special quartz boats ‘For some processes, established
production workflows needed to be accelerated, other processes needed to be reinvented from scratch,’ explains Dr Florian Clement, project manager at Fraunhofer ISE. ‘Compared to the numbers we currently see, the production systems developed within the scope of the project achieve at least double the throughput.’ One of the new developments saw the
researchers implement new on-the-fly laser equipment which continually processes the wafers as they move at high speed under the laser scanner. For the metallisation of solar cells, the consortium introduced
Ultrafast laser scientist wins ‘Swiss Nobel Prize’
Physics professor Ursula Keller has received the Swiss Science Prize Marcel Benoist for her pioneering work in ultrafast lasers. Her theoretical models and experimental discoveries have repeatedly tested the boundaries of ultrafast laser physics. Scientists see the Marcel Benoist Prize, worth 250,000 Swiss francs, as a type of Swiss Nobel Prize. It will be awarded on 3 November. Ever since the laser was
invented, scientists have been keen to use the technology – to transform materials, for example. Unfortunately this was not possible with continuous- wave lasers, as they were too imprecise, and unsuitable for heat-sensitive materials. The eventual solution was to
use a pulsed laser beam, although this required more complex technology. ETH Professor Ursula Keller solved the problem by using semiconductors, and in 1991 invented semiconductor saturable absorber mirror (SESAM) technology. With SESAM, she handed science, industry and medicine a new instrument that enabled previously unimaginably precise interventions. SESAM makes it possible to send light pulses from solid-state lasers at femtosecond intervals. One femtosecond is equivalent to one millionth of one billionth of a second (10-15). Over this incredibly short time it is possible to measure the movement of atoms, for example, or investigate the mechanisms of chemical reactions.
Keller was first female
appointed as professor of physics at ETH Zurich almost 30 years ago, which she said was partly ‘thanks to a policy of recruiting more female scientists to leadership roles.’ As professor of physics,
Keller has continued to develop the SESAM concept. She also succeeded in producing ever shorter laser pulses, until only one or two light oscillations were contained in one laser pulse. However, these oscillations were not synchronised from one pulse to the next, which was a critical factor for the development of further applications. The solution to this problem
led to a revolution in frequency measurement and the invention of the most accurate clocks in
Swiss Science Prize Marcel Benoist winner Ursula Keller
the world: the ‘optical clock’ and the ‘attoclock’. The optical clock allows time measurement to be improved by a factor of roughly five in comparison with existing standards. The attoclock is so accurate that it can measure the fundamental processes of quantum mechanics, such as the speed of electron tunnelling.
rotary screen printing instead of the current standard process, flatbed screen printing. Solar cells require differently doped sections, for example where silicon layer and metal contacts meet. The Fraunhofer ISE researchers integrated the diffusion process used in this context and the thermal oxidation of the wafers into one process step. Wafers are no longer placed individually but stacked on top of each other to be processed in the furnace. As a result, the oxidation process creates the final doping profile and achieves surface passivation at the same time increasing the throughput of the process by a factor of 2.4.
www.electrooptics.com | @electrooptics
November 2022 Electro Optics 5
Heidi Hostettler
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