The annual SiliconPV conference visited TU Delft in the Netherlands last week and provided an important health check for the science and technology behind solar energy. pv magazine was there to hear the latest researchers working to improve efficiency with tandem cells and other innovations, and to reduce the consumption of rare and expensive materials in solar technology.
And the discussions at the event were somewhat urgent. This year’s SiliconPV coincided with the release in Science from an article written by many of the leading figures in the global solar industry and research community entitled “Photovoltaics at terawatt scale: Waiting is not an option”.
Arthur Weeber, conference chairman of the Dutch research organization TNO, stated in his opening speech based on this publication that the world needs 75 TW of solar electricity by 2050 and that the EU should define it as a strategically very important technology. to accelerate efforts to bring full value chain manufacturing back to the region.
Weeber went on to state that industrially, solar energy is at an inflection point, as the current generation of PERC technology will almost completely disappear by 2025. And the n-type technologies that replace it are a big step forward, but we need modules with at least 30 percent efficiency to meet the 2050 renewable energy goals.
The conference moved along this urgent line, and the close connection between PV researchers and industry was much more evident than in previous years, when the transition to a larger scale seemed only a dot on the horizon.
However, a large part of the work presented this year focused on processes and solutions suitable for industrial use. Those where it was less obvious were always followed by a series of questions about larger device size, industrial applicability, material usage, and more.
In some ways, the situation is the opposite – researchers have to keep up with the activities of the field faster than expected. Gallium doping as a solution to mitigate the degradation caused by the elevated temperature of light (more on this later) was practically implemented throughout the industry in about a year, and researchers are still investigating possible wider effects. Meanwhile, many labs still seem to be working with the older 166mm or smaller cell formats, while commercial formats today are almost all based on 182mm or 210mm products.
The material matters
Following a trend of industrial awareness, SiliconPV this year revealed a strong focus on ending solar’s reliance on rare or expensive materials that are unsuitable for the industry’s growing scale and shrinking costs.
In Thursday morning’s session on heterojunction technology, four of the six presentations dealt with ways to reduce or remove indium from the bill of materials, and there were several innovative solutions: CEA Ines’ Tristan Gageot spoke about the challenges of slimming down indium tin oxide. layer 20 nm to 15, 10 or even 5 nm. And Anamaria Steinmetz of Fraunhofer ISE demonstrated a cell that could completely remove indium. Both researchers rely on adding a layer of nanocrystalline silicon to the stack to achieve this, which remains a promising approach but difficult to implement in a large-scale deposition process.
The need to cut silver from all types of solar cells is already well documented. Copper or silver-plated copper has made a lot of progress as replacements. This year it was interesting to note that more work was focused on aluminum pastes, which have the advantages of further industrial development and can be used in the same screen printing processes that cell manufacturers have used for a long time.
We are not far from weakening
In keynote sessions on the first morning of the conference, Wolfram Kwapil of the University of Freiburg described light-elevated-temperature-induced decay (LETID) as “a PERC-era phenomenon, and Tarek Abdul Fattah of the University of Manchester outlined the state of the art – we know that the LETID mechanism involves hydrogen atoms and is affected by dopant properties, but little else it has been agreed.
Switching to gallium doping certainly makes the cells less susceptible to LETID-induced performance degradation, but it cannot be said to completely eliminate it. Various combustion process changes have also been shown to improve LETID performance, but work remains to be done.
Fully elucidating the mechanisms underlying LETID has become an important goal for PV researchers. A number of advanced models to explain the performance degradation were also presented, along with advanced imaging techniques aimed at tracking the behavior of hydrogen atoms in the material.
Bram Hoex of the University of New South Wales also shared new work on potential degradation, noting that this has been a growing problem in recent years due to the degradation mechanism affecting bifacial modules, particularly the rear. Hoex warned that newer TOPcon and HJT modules may also be more susceptible to PID than current modules, and outlined a new testing protocol to detect it early.
Tandems are the future (but not quite the present yet)
In his keynote speech at this year’s conference, Rutger Schlatmann of the Helmholtz Zentrum Berlin noted that the efficiency of solar electricity has increased by an average of 0.6% per year since the first cells were manufactured in the 1960s. He described perovskite-silicon tandem cells as the “missing link” in keeping the technology on this trajectory, noting further that there is a lot of knowledge in Europe to do this.
A later session on tandem cell research revealed a closer connection to industry than previously mentioned. Much of the work focused on optimizing the silicon cell processing for further integration into the second top cell, and the addition of a nickel oxide layer mentioned by a few researchers is a potentially useful innovation.