Secret Hidden in Grains of Perovskite Could Boost Solar Cell Efficiency

A path towards 31-percent conversion efficiency could be possible for perovskite photovoltaics

2 min read
Map of crystal facets in a perovskite photovoltaic.
Image: Berkeley Lab

The rise of the crystal perovskite as a potential replacement for silicon in photovoltaics has been impressive over the last decade, with its conversion efficiency improving from 3.8 to 22.1 percent over that time period. Nonetheless, there has been a vague sense that this rise is beginning to peter out of late, largely because when a solar cell made from perovskite gets larger than 1 square centimeter the best conversion efficiency had been around 15.6 percent. This figure has been improved recently in the work of Michael Grätzel to an average of 19.6 percent.  However, the bright prospects for perovskite have dimmed in eyes of some.

Now researchers at the Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab) may have discovered something hidden in perovskite crystals that could boost the conversion efficiency of this material to as high as 31 percent.

In research described in the journal Nature Energy, the researchers peered into the nanoscale structure of these crystals with atomic force microcscopy. At that scale they found that each facet of each grain of the crystal performed differently in terms of conversion efficiency. Some facets of the crystal would have the theoretical conversion limit of 31 percent and these would be adjacent to facets with poor conversion efficiency.

Each facet of the perovskite acts as an individual solar cells and all of them are connected in parallel. In this arrangement, the current flows towards those cells that have the worst performance, leading to a lowering of the overall performance of the solar cell.

The researchers hit upon the idea of making all the facets of the crystal reach the goal of 31-percent conversion efficiency.

“If the material can be synthesized so that only very efficient facets develop, then we could see a big jump in the efficiency of perovskite solar cells, possibly approaching 31 percent,” said Sibel Leblebici, a postdoctoral researcher at the Molecular Foundry at Berkeley Lab, in a press release.

The researchers mapped the surface of perovskite solar cells at the resolution of 10 nanometers and also mapped the properties of photocurrent generation and open circuit voltage, which relate to conversion efficiency.

The maps revealed that there was as much as an order of magnitude difference between each facet in terms of photocurrent generation and a difference of 0.6 volts in open circuit voltage.

The real surprise for the researchers was to discover that facets with a high photocurrent generation had a high open circuit voltage, and those facets with a low photocurrent generation had a low open circuit voltage. This means that perovskite solar cells have facet-dependent photovoltaic efficiency.

“These results open the door to exploring new ways to control the development of the material’s facets to dramatically increase efficiency,” said Francesca Toma, one of the researchers, in a press release.

While the researchers have not yet made this optimized perovskite, they have developed a computer model that demonstrates that these facets should also impact the emission of light when used as an LED.

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Smokey the AI

Smart image analysis algorithms, fed by cameras carried by drones and ground vehicles, can help power companies prevent forest fires

7 min read
Smokey the AI

The 2021 Dixie Fire in northern California is suspected of being caused by Pacific Gas & Electric's equipment. The fire is the second-largest in California history.

Robyn Beck/AFP/Getty Images

The 2020 fire season in the United States was the worst in at least 70 years, with some 4 million hectares burned on the west coast alone. These West Coast fires killed at least 37 people, destroyed hundreds of structures, caused nearly US $20 billion in damage, and filled the air with smoke that threatened the health of millions of people. And this was on top of a 2018 fire season that burned more than 700,000 hectares of land in California, and a 2019-to-2020 wildfire season in Australia that torched nearly 18 million hectares.

While some of these fires started from human carelessness—or arson—far too many were sparked and spread by the electrical power infrastructure and power lines. The California Department of Forestry and Fire Protection (Cal Fire) calculates that nearly 100,000 burned hectares of those 2018 California fires were the fault of the electric power infrastructure, including the devastating Camp Fire, which wiped out most of the town of Paradise. And in July of this year, Pacific Gas & Electric indicated that blown fuses on one of its utility poles may have sparked the Dixie Fire, which burned nearly 400,000 hectares.

Until these recent disasters, most people, even those living in vulnerable areas, didn't give much thought to the fire risk from the electrical infrastructure. Power companies trim trees and inspect lines on a regular—if not particularly frequent—basis.

However, the frequency of these inspections has changed little over the years, even though climate change is causing drier and hotter weather conditions that lead up to more intense wildfires. In addition, many key electrical components are beyond their shelf lives, including insulators, transformers, arrestors, and splices that are more than 40 years old. Many transmission towers, most built for a 40-year lifespan, are entering their final decade.

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