Can Organic Solar Cells Reach Old Age?

Engineers report progress on keeping organic photovoltaics alive

2 min read
Can Organic Solar Cells Reach Old Age?
Photo: NIST

Although organic photovoltaic cells are less efficient than silicon-based ones, experts expect their to one day be a big market for them. That’s because they are cheap to manufacture, flexible, and light-weight. However, there is a big obstacle to their wide-scale use: their lifetime is limited by oxygen and by ultraviolet radiation.

There’s hope, according to Monica Lira-Cantu, an engineer investigating organic solar photovoltaics at the Catelan Institute of Nanoscience and Nanotechnology in Bellaterra, Spain. She was one of the three organizers of ISOS-7 International Summit on OPV Stability (ISOS) held in Barcelona, on 6-8 October.

"The technology controlling the stability of organic solar cells is really advancing; they are getting more stable each year, and that is what we need to reach the market, " she says. Niche markets might open up earlier: "The application of organic solar cells for short-term applications is clear, such as mobile applications or military applications," she says.

We have to do something about organic solar lifetimes because researchers from industry are publishing values all over the place

Determining the lifetime of an organic photovoltaic cell has been fraught with difficulties from the beginning of OPV research. "ISOS 1 was started in 2008 when competing companies got together and said, 'OK we have to do something about organic solar lifetimes because researchers from industry are publishing values all over the place' ," says Moritz Riede, a physicist at the University of Oxford , and also organizer of the summit. "We wanted to make sure that solar cells are being measured under comparable conditions, and that the lifetimes that are cited can stand up to scrutiny," says Riede.

In response, ISOS developed measurement protocols, such as specifications for climate chambers and for certified light sources. "These are not yet international standards, but they are recommendations, so people know better under which circumstances the lifetime of a photovoltaic cell was obtained," says Riede.

Another complication is that the definition of "lifetime" can vary. Usually it is defined as the time it takes for a decrease of the initial efficiency to 80 percent, but there is a less common definition, used by the International Electrotechnical Commission that allows cells to degrade only by 10 percent.

Further, the proliferation of a huge number of organic PV cells is complicating things further. "There is no 'the organic solar cell;' there are thousands of compounds and even millions of ways you can combine the compounds into solar cells," says Riede. Even with identical materials, you can obtain different results depending on which electrodes you use. With some test conditions the efficiency may even increase for the first 1000 hours, and then slowly degrade, he says.

Notwithstanding all these complexities, Riede and Lira-Cantu identified some notable progress:

  • Solliance showed 7000 hours of damp-heat stability (85°C, 85 percent relative humidity) for fully flexible organic solar modules with barrier technology developed at the Holst Centre and device technology of one of their partners.
  • Heliatek showed over 22,000 hours light stability (under a halogen light) on a high performance 2.3-meter-long organic solar module encapsulated in glass and built on from its fabrication line.
  • Solar modules from Chose reported efficiencies of  7-13  percent depending on the device structure and detailed a one or two step process for perovskite deposition.
  • TU Dresden showed improved stress resistance and enhanced performance of flexible barriers by combining atomic layer deposition with molecular layer deposition.

 Most of the talks will be made available online at the ISOS website.

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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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