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Robotic Research Platform Discovers New, More Efficient Material For Solar Cells

Rows of solar panels standing in a field.
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Researchers at North Carolina State University (NC State) have developed a new robotic materials acceleration platform (MAP), named the RoboMapper, that can rapidly synthesize and print new semiconductor materials.

In a demonstration of the RoboMapper platform, published in the journal Matter, the researchers also report the discovery of a new group of alloys that have the potential to outperform classic silicon solar cells when it comes to generating electricity from light.

Automating materials science experiments

Semiconductors are an essential aspect of today’s modern technologies, underpinning everything from electronics to transportation to clean energy. Developing a broad range of novel semiconductor materials is one of the key ways in which materials scientists are hoping to further these advancements and create new technological breakthroughs.

But conventional materials research is tricky. Despite attempts to automate what can be thought of as the “assembly line”, where a researcher prepares a new sample and sends it through multiple different instruments for analysis, current workflows are still very lengthy. One at a time, samples must be placed, aligned and calibrated, before being sent through a series of different analysis instruments to collect relevant data.

What is a semiconductor?

A semiconductor can be thought of as a material that conducts more electricity than insulators (such as rubber), but less than a pure conductor (like copper wire). By introducing different impurities into a semiconductor – through a process known as “doping” – it is possible to tune the conductivity of semiconductors to suit the applications they are needed for.

Semiconductors have found widespread use in a plethora of industries. Many semiconducting materials also display rather novel properties, such as the ability to react to light or heat, which makes them useful for energy conversion. Semiconductors are also a major part of the computing industry, where they are used to manage the flow of electrical current through complex electronic circuits.

In a bid to improve on current MAP systems, researchers at NC State sought to develop a new kind of robotics platform that can prepare dozens of semiconductor samples at once for testing. The platform they built is called the RoboMapper.

“RoboMapper allows us to conduct materials testing more quickly, while also reducing both cost and energy overhead – making the entire process more sustainable,” said study author Aram Amassian, a professor of materials science and engineering at NC State.

“RoboMapper also automates this process, but places dozens of samples on each chip by miniaturizing the material samples with the help of modern printing,” Amassian explained. “It still performs each step of the data collection process, but it does so for multiple materials in parallel, saving time and energy.”

The need for new perovskite materials

The new Matter paper focuses on a proof-of-concept study, intended to demonstrate the utility of RoboMapper in analyzing a large volume of perovskite material samples.

Perovskites are family materials with a very specific crystal structure; one that has shown great potential for different nanotechnology applications.

Here, perovskites are of interest to those working in the energy sector as they are better than silicon at absorbing light. That means that a solar cell (and by extension, full-sized solar panels) made from perovskites can be thinner and lighter than traditional silicon solar cells – without having any detrimental impact on the cell’s ability to convert light into electricity.

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However, in a strange twist of fate, perovskite materials come with one big problem. They tend to be rather unstable under strong light.

“Basically, the challenge is that perovskite materials tend to degrade when exposed to light, losing the properties that made them desirable in the first place,” Amassian said. “We’re looking for ways to engineer these materials so that they are stable – meaning they retain their desirable properties for a long time, even when exposed to light.”

RoboMapper discovers new material for solar cells

In their new study, the researchers programmed the RoboMapper to make alloys using a defined set of elements. In total, the platform created 150 unique alloy compositions, then conducted optical spectroscopy and X-ray structural assessments on the miniaturized samples.

RoboMapper’s tests were geared towards discovering which alloys had the favorable perovskite structure, and which also had the favorable optical and electronic properties that were needed to maintain stability and generate electricity under intense light.

After this initial round of testing, RoboMapper’s results were fed into a computer model to determine a specific alloy composition that should have the most optimal set of physical, optical and electronic attributes for a solar cell. This ideal alloy was then produced by both RoboMapper and the researchers using traditional techniques, before testing both.

“We are able to quickly identify the most stable composition from a possible set of perovskite alloys at a target band gap using the specific suite of elements we confined ourselves to for this proof-of-concept work,” Amassian said. “The material we identified using RoboMapper also turned out to be more efficient at converting light into electricity in solar cell devices.”

“Next steps for this work include expanding the range of potential alloys for testing in RoboMapper,” Amassian said. “We’re open to working with industry partners to identify new materials for photovoltaics or other applications. And with support from the Office of Naval Research, we are already using RoboMapper to advance our understanding of materials for both organic solar cells and printed electronics.”

Robotics as a greener approach to materials research

In addition to the perovskite experiment, the Matter paper also includes additional life cycle assessments which compare the environmental impacts of using the RoboMapper, versus other automated MAPs or manual experimentation.

The researchers determined that the RoboMapper was around 14 times faster than a fully manual process and 9 times faster than other automated procedures. Despite its use of robotics, the RoboMapper also performed favorably in life cycle analyses looking at cost and energy savings – where the RoboMapper was 18 times more energy efficient than existing MAPs.

“This makes searching for new materials far more efficient, more cost-effective and more sustainable in terms of our carbon footprint,” said Tonghui Wang, lead author of the paper and a PhD student at NC State. “It’s nearly 10 times faster than previous automated techniques.”

“It was remarkable to find that characterization is the major source of greenhouse gas emissions in materials research,” added environmental economist Lucía Serrano-Luján, study co-author and a researcher at Rey Juan Carlos University and the Technical University of Cartagena. “The RoboMapper’s ability to streamline the data collection process by placing dozens of materials on the same chip reduced greenhouse gas emissions 10-fold.”

Reference: Wang T, Li R, Ardekani H et al. Sustainable materials acceleration platform reveals stable and efficient wide-bandgap metal halide perovskite alloys. Matter. 2023;6:1-24. doi: 10.1016/j.matt.2023.06.040

This article is a rework of a press release issued by North Carolina State University. Material has been edited for length and content.