Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Solvents save steps in solar cell manufacturing

20.10.2015

Advances in ultrathin films have made solar panels and semiconductor devices more efficient and less costly, and researchers at the Department of Energy's Oak Ridge National Laboratory say they've found a way to manufacture the films more easily, too.

Typically the films--used by organic bulk heterojunction solar cells, or BHJs, to convert solar energy into electricity--are created in a solution by mixing together conjugated polymers and fullerenes, soccer ball-like carbon molecules also known as buckyballs.


Fullerenes appear as small silver spheres spread consistently throughout a network of small molecules, or polymers, in this schematic illustration of the morphology of a BHJ film with solvent additives.

Credit: Oak Ridge National Laboratory

Next, the mixture is spin cast on a rotating substrate to ensure uniformity, then sent to post-processing to be annealed. Annealing the material--heating then cooling it--reduces the material's hardness while increasing its toughness, which makes it easier to work with.

Pliability makes BHJs more appealing than their more costly crystalline silicon counterparts, but the annealing process is time consuming.

Now ORNL researchers say a simple solvent may make thermal annealing a thing of the past.

In a collaboration between ORNL's Spallation Neutron Source (SNS) and the Center for Nanophase Materials Sciences (CNMS)--both DOE Office of Science User Facilities--postdoctoral researcher Nuradhika Herath led a team of neutron and materials scientists in a study of the morphology, or structure, of BHJ films.

"Optimizing a film's morphology is the key to improving device performance," Herath said. "What we want to find out is the relationship between the blend structures and photovoltaic performance." Finding ways to tune the film's morphology is as important as answering why certain film morphologies are more favorable than others, she added.

Researchers compared thermal annealing with a method that adds a small amount of solvent that aids in dissolving the fullerenes within the blend and helps to make the film's structure more uniform.

The idea is to get the most uniform mixture of light absorbing molecules (e.g., polymers or other molecules) and fullerenes throughout the film. If the mixture is not uniform, clusters form and cause passing electrons to get absorbed, weakening the film's ability to transport electrical current, which in turn decreases device performance.

Because the films are typically about 100 nanometers thick (for comparison, a human hair is about 75,000 nanometers in diameter) and the depth profile of the composition is highly complex, special instruments are needed to measure the material's morphology. For this, researchers turned to neutron scattering.

After mixing and spin casting two different samples at CNMS--one annealed, the other with solvent additive--the team put both films under the eye of SNS's Magnetism Reflectometer (MR), beam line 4A. MR provided them with an accurate depiction of the structural profiles, which revealed exactly how the polymers and fullerenes were arranging themselves throughout both films. The difference between them was evident.

Whereas the annealed sample's morphology clearly showed significant separation between the polymers and fullerenes, the sample containing the solvent additive was remarkably consistent throughout and performed better.

"The reason is that when we use a solvent instead of annealing, the sample dries very slowly, so there is enough time for the system to become fully optimized," said MR Lead Instrument Scientist Valeria Lauter. "We see that additional annealing is not necessary because, in a sense, the system is already as perfect as it can be."

Neutron reflectometry is a powerful method because it effectively makes many materials transparent, Lauter explained. Instead of searching for the key that opens the metaphorical black box that prevents researchers from seeing a material's atomic structure, she says, neutrons simply go straight through it, giving researchers both qualitative and quantitative information about their problem.

Not only will the information obtained from neutrons help increase the efficiency of solar cells' performance, but they will also streamline the process of manufacturing them. Using solvent additives to optimize the morphology of BHJ films could negate the need to invest more into a less effective process--a savings of time, money, and resources.

"In addition, optimization of photovoltaic properties provides information to manufacture solar cells with fully controlled morphology and device performance," Herath said. "These findings will aid in developing 'ideal' photovoltaics, which gets us one step closer to producing commercialized devices."

###

The researchers discuss their findings in the journal Scientific Reports, 5, 13407 (2015).

Herath's coauthors include Sanjib Das and Gong Gu from the University of Tennessee; and ORNL's Jong K. Keum, Jiahua Zhu, Rajeev Kumar, Ilia N. Ivanov, Bobby G. Sumpter, James F. Browning, Kai Xiao, Pooran Joshi, Sean Smith and Valeria Lauter.

This research used resources of the Spallation Neutron Source and the Center for Nanophase Materials Sciences at ORNL, which are DOE Office of Science User Facilities.

Media Contact

Jeremy Rumsey
rumseyjp@ornl.gov
865-576-2038

 @ORNL

http://www.ornl.gov 

Jeremy Rumsey | EurekAlert!

More articles from Power and Electrical Engineering:

nachricht Researchers take next step toward fusion energy
16.11.2017 | Texas A&M University

nachricht Desert solar to fuel centuries of air travel
16.11.2017 | SolarPACES

All articles from Power and Electrical Engineering >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: A “cosmic snake” reveals the structure of remote galaxies

The formation of stars in distant galaxies is still largely unexplored. For the first time, astron-omers at the University of Geneva have now been able to closely observe a star system six billion light-years away. In doing so, they are confirming earlier simulations made by the University of Zurich. One special effect is made possible by the multiple reflections of images that run through the cosmos like a snake.

Today, astronomers have a pretty accurate idea of how stars were formed in the recent cosmic past. But do these laws also apply to older galaxies? For around a...

Im Focus: Visual intelligence is not the same as IQ

Just because someone is smart and well-motivated doesn't mean he or she can learn the visual skills needed to excel at tasks like matching fingerprints, interpreting medical X-rays, keeping track of aircraft on radar displays or forensic face matching.

That is the implication of a new study which shows for the first time that there is a broad range of differences in people's visual ability and that these...

Im Focus: Novel Nano-CT device creates high-resolution 3D-X-rays of tiny velvet worm legs

Computer Tomography (CT) is a standard procedure in hospitals, but so far, the technology has not been suitable for imaging extremely small objects. In PNAS, a team from the Technical University of Munich (TUM) describes a Nano-CT device that creates three-dimensional x-ray images at resolutions up to 100 nanometers. The first test application: Together with colleagues from the University of Kassel and Helmholtz-Zentrum Geesthacht the researchers analyzed the locomotory system of a velvet worm.

During a CT analysis, the object under investigation is x-rayed and a detector measures the respective amount of radiation absorbed from various angles....

Im Focus: Researchers Develop Data Bus for Quantum Computer

The quantum world is fragile; error correction codes are needed to protect the information stored in a quantum object from the deteriorating effects of noise. Quantum physicists in Innsbruck have developed a protocol to pass quantum information between differently encoded building blocks of a future quantum computer, such as processors and memories. Scientists may use this protocol in the future to build a data bus for quantum computers. The researchers have published their work in the journal Nature Communications.

Future quantum computers will be able to solve problems where conventional computers fail today. We are still far away from any large-scale implementation,...

Im Focus: Wrinkles give heat a jolt in pillared graphene

Rice University researchers test 3-D carbon nanostructures' thermal transport abilities

Pillared graphene would transfer heat better if the theoretical material had a few asymmetric junctions that caused wrinkles, according to Rice University...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Ecology Across Borders: International conference brings together 1,500 ecologists

15.11.2017 | Event News

Road into laboratory: Users discuss biaxial fatigue-testing for car and truck wheel

15.11.2017 | Event News

#Berlin5GWeek: The right network for Industry 4.0

30.10.2017 | Event News

 
Latest News

Antarctic landscape insights keep ice loss forecasts on the radar

20.11.2017 | Earth Sciences

Filling the gap: High-latitude volcanic eruptions also have global impact

20.11.2017 | Earth Sciences

Water world

20.11.2017 | Life Sciences

VideoLinks
B2B-VideoLinks
More VideoLinks >>>