Incheon National University researchers have demonstrated the first transparent solar cell. Their innovative technique rests on a specific part of the solar cell: the heterojunction, made up of thin films of materials responsible for absorbing light. By combining the unique properties of titanium dioxide and nickel oxide semiconductors, the researchers were able to generate an efficient, transparent solar cell.

In recent decades, solar cells have become cheaper, more efficient, and environment friendly. However, current solar cells tend to be opaque, which prevents their wider use and integration into everyday materials, constrained to being lined up on roofs and in remote solar farms.

The solar cell created by the team is transparent, allowing its use in a wide range of applications. Image Credit: Joondong Kim, Incheon University. Click image for the largest view.

But what if next-generation solar panels could be integrated to windows, buildings, or even mobile phone screens? That is the hope of Professor Joondong Kim from the Department of Electrical Engineering at Incheon National University, Korea.

In a recent study published in Journal of Power Sources, he and his colleagues detail their latest invention: a fully transparent solar cell. “The unique features of transparent photovoltaic cells could have various applications in human technology,” said Prof. Kim.

The idea of transparent solar cells is well known, but this novel application where scientists have been able to translate this idea into practice is a crucial new finding. At present, the materials making the solar cell opaque are the semiconductor layers, those responsible for capturing light and translating it into an electrical current. Hence, Prof. Kim and his colleagues looked at two potential semiconductor materials, identified by previous researchers for their desirable properties.

The first is titanium dioxide (TiO2), a well-known semiconductor already widely used to make solar cells. On top of its excellent electrical properties, TiO2 is also an environment-friendly and non-toxic material. This material absorbs UV light (a part of the light spectrum invisible to the naked eye) while letting through most of the visible light range. The second material investigated to make this junction was nickel oxide (NiO), another semiconductor known to have high optical transparency. As nickel is one of the most abundant elements on Earth, and its oxide can easily be manufactured at low industrial temperatures, NiO is also a great material to make eco-friendly cells.

The solar cell prepared by the researchers was composed of a glass substrate and a metal oxide electrode, on top of which they deposited thin layers of the semiconductors (TiO2 first, then NiO) and a final coating of silver nanowires, acting as the other electrode in the cell. They ran several tests to evaluate the device’s absorbance and transmittance of light, as well as its effectiveness as a solar cell.

Their findings were encouraging; with a power conversion efficiency of 2.1%, the cell’s performance was quite good, given that it targets only a small part of the light spectrum. The cell was also highly responsive and worked in low light conditions. Furthermore, more than 57% of visible light was transmitted through the cell’s layers, giving the cell this transparent aspect. In the final part of their experiment, the researchers demonstrated how their device could be used to power a small motor. “While this innovative solar cell is still very much in its infancy, our results strongly suggest that further improvement is possible for transparent photovoltaics by optimizing the cell’s optical and electrical properties,” suggested Prof. Kim.

Now that they have demonstrated the practicality of a transparent solar cell, they hope to further improve its efficiency in the near future. Only further research can tell whether they will indeed become a reality, but for all intents and purposes, this new technology opens quite literally, a window into the future of clean energy.

This team has done something very interesting. One might temper the excitement noting the limited spectrum gathered and about half the visible light still blocked. On the other hand, the team has almost two thirds of the light coming through and they’re getting the hard to catch ultra violet generating power. That’s two impressive accomplishments. This tech now has some legs to run on for more innovation and research.

Kyushu University researchers have a blue light source organic light-emitting diode matching the excellent performance of the red and green ones. Using a new combination of emitter molecules, the researchers have demonstrated the promise of a novel approach to finally overcome a major challenge facing displays with high efficiency, maintaining brightness for a relatively long time, and without any expensive metal atoms.

By splitting energy conversion and emission processes between two molecules, the researchers achieved the devices that produce pure-blue emission. Acclaimed for their vibrant colors and ability to form thin and even flexible devices, organic light-emitting diodes, or OLEDs for short, use carbon-containing molecules to convert electricity into light.

The molecule HDT-1 rapidly converts non-emitting triplets into singlets and transfers the energy to ν-DABNA for pure-blue emission. Use of a tandem structure further improved color purity and lifetime. Image Credit: Kyushu University. Click image for the largest view.

Unlike LCD technologies employing liquid crystals to selectively block emission from a filtered backlight covering many pixels, the separate red, green, and blue emitting pixels of an OLED display can be completely turned on and off individually, producing deeper blacks and reducing power consumption.

However, blue OLEDs in particular have been a bottleneck in terms of efficiency and stability.

The researchers have reported the study results in Nature Photonics.

Chin-Yiu Chan, a researcher at Kyushu University’s Center for Organic Photonics and Electronics Research (OPERA) and author on the study said, “A growing number of options exist for red and green OLEDs with excellent performance, but devices emitting high-energy blue light are more of a challenge, with tradeoffs almost always occurring among efficiency, color purity, cost, and lifetime.”

While stable blue emitters based on a process known as fluorescence are often used in commercial displays, they suffer from a low maximum efficiency. So-called phosphorescent emitters can achieve an ideal quantum efficiency of 100%, but they generally exhibit shorter operational lifetimes and require an expensive metal such as iridium or platinum.

As an alternative, OPERA researchers have been developing molecules that emit light based on the process of thermally activated delayed fluorescence, commonly abbreviated as TADF, which can achieve excellent efficiency without the metal atom but often exhibits emission containing a wider range of colors.

Chihaya Adachi, director of OPERA explained, “The range of colors a display can produce is directly related to the purity of the red, green, and blue pixels. If blue emission is not pure with a narrow spectrum, filters are needed to improve the color purity, but this wastes emitted energy.”

Takuji Hatakeyama’s group at Kwansei Gakuin University recently reported a promising path to overcome the purity issue based on a unique molecular design for a highly efficient, pure-blue TADF emitter, but the molecule, named ν-DABNA, quickly degrades under operation.

Collaborating with Hatakeyama, the OPERA researchers have now found that lifetime can be greatly improved while still obtaining narrow emission by combining ν-DABNA with an additional TADF molecule developed at OPERA as an intermediate, high-speed energy converter.

“Three-fourths of electrical charges combine to form energy states called triplets in OLEDs, and TADF molecules can convert these non-emitting triplets into light-emitting singlets,” explained Masaki Tanaka, an OPERA researcher who worked closely with Chan on the study. “However, ν-DABNA is somewhat slow at converting the high-energy triplets, which often play a role in degradation. To get rid of the dangerous triplets more quickly, we included an intermediary TADF molecule that can more rapidly convert triplets into singlets.”

Though the intermediary molecule is fast at converting triplets to singlets, it has a wide emission spectrum producing a sky-blue emission. Nonetheless, the intermediary can transfer many of its singlets in a high-energy state to ν-DABNA for fast and pure blue emission.

“Compared to most emitters, the wavelengths that ν-DABNA can absorb are very close to the color it emits. This unique property makes it able to receive much of the energy from the wide-emission intermediary and still emit a pure blue,” said Chan.

Using this two-molecule approach, which has been termed hyperfluorescence, the researchers achieved longer operational lifetimes at high brightness than previously reported for highly efficient OLEDs having a similar color purity.

“That this kind of approach can extend the lifetime of pure-blue emission from a molecule we previously developed is really exciting,” says Hatakeyama.

Adopting a tandem structure that basically stacks two devices on top of each other to effectively double the emission for the same electrical current, lifetime was nearly doubled at high brightness, and the researchers estimated that devices could maintain 50% of their brightness for over 10,000 hours at more moderate intensities.

“Though this is still too short for practical applications, stricter control of fabrication conditions often leads to even longer lifetimes, so these initial results point to a very promising future for this approach to finally obtain an efficient and stable pure-blue OLED,” said Adachi.

“In the near future, I hope that blue hyperfluorescence OLEDs can replace current blue OLEDs for ultra-high-definition displays,” added Chan.

This development could very well bring the OLED TVs and monitors to a very high color performance level and as manufacturing scales up, perhaps even lower costs to go along with the energy savings. Things have already come a very long way from the old CRT monitors, and there is more to come.

Oak Ridge National Lab researchers are accelerating a research engine that gives scientists and engineers an unprecedented view inside the atomic-level workings of combustion engines in real time. The effort seeks to support advanced vehicles with higher energy efficiency and ultra-low emissions.

The new capability is an engine built specifically to run inside a neutron beam line. This neutronic engine provides a unique sample environment that allows investigation of structural changes in new alloys designed for the environment of a high-temperature, advanced combustion engine operating in realistic conditions.

Researchers Martin Wissink, left, and Ke An worked with colleagues to design and test a running combustion engine prototype in the VULCAN beamline at the Spallation Neutron Source at ORNL, proving a new, non-destructive capability to analyze materials for advanced vehicles at the atomic level in a realistic setting. Image Credit: Genevieve Martin/ORNL. Click image for the largest view.

ORNL first unveiled the capability in 2017, when researchers successfully evaluated a small, prototype engine with a cylinder head cast from a new high-temperature aluminum-cerium alloy created at the lab. The experiment was the world’s first in which a running engine was analyzed by neutron diffraction, using the VULCAN neutron diffractometer at the Department of Energy’s Spallation Neutron Source, or SNS, at ORNL.

The results of the research, published in the Proceedings of the National Academy of Sciences, not only proved the hardiness of the unique alloy, but also demonstrated the value of using non-destructive methods such as neutrons to analyze new materials.

Neutrons are deeply penetrating even through dense metals. When neutrons scatter off atoms in a material, they provide researchers with a wealth of structural information down to the atomic scale. In this case, scientists determined how the alloys perform in operating conditions such as high heat and extreme stress or tension to identify even the smallest defects.

The experiment’s success has prompted ORNL to design a purpose-built research engine at industry-relevant scale for use in VULCAN. The capability is based on a two-liter, four-cylinder automotive engine, modified to operate on one cylinder to conserve sample space on the beamline. The engine platform can be rotated around the cylinder axis to give maximum measurement flexibility. The engine is custom designed for neutron research, including the use of fluorocarbon-based coolant and oil, which improves visibility into the combustion chamber.

The capability will provide researchers with the experimental results they need to quickly and accurately vet new materials and improve high-fidelity computational models of engine designs.

Martin Wissink, lead of the project at ORNL said, “Around the world, industry, national labs and academia are looking at the interface between turbulent combustion that happens in the engine, and the heat transfer process that happens through the solid components. Understanding and optimizing that process is really key to improving the thermal efficiency of engines. But currently, most of these models have almost no in situ validation data. The objective is to fully resolve stress, strain, and temperature in the entire domain over all the metal parts in the combustion chamber.”

The engine has been designed to ORNL specs and is currently undergoing final development with the Southwest Research Institute, and will be commissioned at DOE’s National Transportation Research Center, or NTRC, at ORNL before its first use at SNS, which is expected by late 2021. Both the NTRC and SNS are DOE scientific user facilities, providing access to the most advanced tools of modern science to researchers around the world.

The VULCAN instrument at the SNS is ideal for the research, as it accommodates larger structures, said Ke An, lead scientist for the instrument. VULCAN is designed for deformation, phase transformation, residual stress, texture and microstructure studies. According to An, they are preparing the platform for the neutronic engine with a new exhaust system and other retrofits, including a new control interface for the engine.

An said, “This is what will get people excited, producing results on a larger, state-of-the-art engine. (The neutronic engine) will provide even more options to users seeking to validate their models to resolve issues like stress, strain and temperature. It shows the direct value of neutrons to an important manufacturing sector.”

Measurements from the neutronic engine will be fed into high-performance computing, or HPC, models being developed by scientists to speed breakthroughs for advanced combustion engines.

Researchers are interested in creating accurate predictions of phenomena such as heat losses, flame quenching and evaporation of fuel injected into the cylinder, especially during cold-start engine operations when emissions are often highest. The data from the neutronic engine are expected to provide new understanding of how the temperature of metal engine components changes throughout the engine over the course of the engine cycle.

The resulting high-fidelity models can be quickly run on supercomputers such as Summit, the nation’s fastest and most AI-capable computer. Summit is housed at ORNL as part of the Oak Ridge Leadership Computing Facility, also a DOE scientific user facility.

“We’re bridging these fundamental science capabilities to applications and making measurements in real engineering devices and systems,” Wissink said. “The full measurement of strains and temperatures in engine components is something that has not been possible before. It’s crucial to have these data as either a validation or as a boundary condition for the HPC models that can be shared with researchers in the automotive industry.”

The neutronic engine augments existing capabilities at ORNL and other national labs in the work to create more energy-efficient and ultra-clean engines, said Robert Wagner, director of ORNL’s Buildings and Transportation Science Division.

“The ability to operate an engine in the neutron beamlines enables us to make unprecedented measurements under realistic engine conditions,” Wagner said. This capability adds to the one-of-a-kind resources that the national laboratories bring to advance the efficiency and emissions of combustion engines, such as the optical engine research at Sandia National Laboratories and with the Advanced Photon Source at Argonne National Laboratory.

The power of these unique resources is currently being aligned to solve the most challenging problems through a six-laboratory consortium called Partnership to Advance Combustion Engines, led out of the DOE Vehicle Technologies Office.

“What sets us apart here at ORNL is the portfolio of science available,” Wagner said. “We are making use of the world’s most powerful neutron source, the nation’s fastest supercomputer, and world-class materials science in coordination with our expertise in transportation to take on the grand challenges of a more sustainable energy future.”

Sometimes the government research looks very useful indeed. The internal combustion engine will be with us for decades to come as the necessity for remote energy use will not go away. More fuel efficiency and cleaner emissions are coming – welcome additions to better standards of living for everyone.

Hiroshima University researchers have blended together various polymer and molecular semiconductors as photo-absorbers to create a solar cell with increased power efficiencies and electricity generation.

These types of solar cells, known as organic photovoltaics (OPV), are devices that generate electricity when light is incident upon their photo-absorbers. The efficiency of a solar cell is determined by comparing how much electricity is generated to how much light is incident upon the cell. This is referred to as “photon harvest,” or how many particles of light are converted into electrical current. The more efficient the solar cell, the more cost effective and pragmatic the cell is for commercial use.

Schematic illustration of the distribution of the materials in the semiconductor layer for the OPV cell.  ITIC is selectively located at the interface of PTzBT and PCBM domains, which leads to an efficient charge carrier (photocurrent) generation. Image Credit: Hiroshima University. Click Image for the largest view.

The team at the Graduate School of Advanced Science and Engineering added only a small amount of a compound that absorbs long wavelengths of light resulting in an OPV that was 1.5 times more efficient than the version without the compound. The compound was able to enhance the absorption intensity due to the optical interference effect within the device. The group went on to show that how they are distributed is key to further improved power generation efficiency.

Itaru Osaka, corresponding author of the paper, published in Macromolecules said, “The addition of a very small amount of a sensitizer material to an OPV cell, which consists of a semiconducting polymer that we developed previously and along with other materials.”

Osaka explained, “This leads to a significant increase in the photocurrent and thereby the power conversion efficiency due to the amplified photon absorption that originates in the optical interference effect. A key is to use a very specific polymer, one that allows us to have a very thick semiconductor layer for OPV cells, which significantly enhances optical interference effect compared to a thin layer.”

As for future work, Osaka has his eye set on pushing the boundaries of state of the art solar cells.

“Our next step is to develop better semiconducting polymers as the host material for this type of OPV and better sensitizer materials that can absorb more photons in the longer wavelength regions. This would lead to the realization of the world’s highest efficiency in OPV cells.”

A 150% gain in efficiency is quite an achievement. Admittedly, organic photovoltaics do have a long way to go to catch semi-conductor solar cells. But, they shouldn’t have to, as they are vastly less expensive to make, and contain way less objectionable material. You can bet manufacturers in this field are taking notice.

Incheon National University scientists encapsulated a methanol fuel cell catalyst in a protective molecular sieve that selectively prevents undesired reactions.

Direct methanol fuel cells (DMFCs), which produce electricity using methanol, will be an alternative solution in the transition away from fossil fuels and toward a ‘hydrogen’ economy. However, undesired methanol oxidation on the cathode side in DMFCs degrades the essential platinum catalyst, causing performance and stability problems. Now, scientists from Korea have found a simple method to coat platinum nanoparticles with a protective carbon shell. This selectively excludes methanol from reaching the catalyst’s core on the cathode, solving a long-standing problem in DMFCs.

Graphic of a synthesized carbon-encapsulated Pt cathode catalyst. Image Credit: Incheon National University. Click image for the largest view.

Many scientists worldwide are focused on finding efficient alternatives. Though high hopes have been placed on hydrogen fuel cells, the reality is that transporting, storing, and using pure hydrogen comes with a huge added cost, making this process challenging with current technology. In contrast, methanol (CH3O3), a type of alcohol, does not require cold storage, has a higher energy density, and is easier and safer to transport, making a transition into a methanol-based economy is a more realistic goal.

However, producing electricity from methanol at room temperature requires a direct methanol fuel cell (DMFC); a device that, so far, offers subpar performance. One of the main problems in DMFCs is the undesired “methanol oxidation” reaction, which occurs during “methanol crossover”, that is, when it passes from the anode to the cathode. This reaction results in the degradation of the platinum (Pt) catalyst that is essential for the cell’s operation. Although certain strategies to mitigate this problem have been proposed, so far none has been good enough owing to cost or stability issues.

In a recent study published in ACS Applied Materials & Interfaces, a team of scientists from Korea came up with a creative and effective solution. They fabricated – through a relatively simple procedure – a catalyst made of Pt nanoparticles encapsulated within a carbon shell. This shell forms an almost impenetrable carbon network with small openings caused by nitrogen defects. While oxygen, one of the main reactants in DMFCs, can reach the Pt catalyst through these “holes,” methanol molecules are too big to pass through.

Professor Oh Joong Kwon from Incheon National University, Korea, who led the study explained, “The carbon shell acts as a molecular sieve and provides selectivity toward the desired reactants, which can actually reach the catalyst sites. This prevents the undesirable reaction of the Pt cores.”

The scientists conducted various types of experiments to characterize the overall structure and composition of the prepared catalyst and proved that oxygen could make it through the carbon shell and methanol could not. They also found a straightforward way to tune the number of defects in the shell by simply changing the temperature during a heat treatment step. In subsequent experimental comparisons, their novel shelled catalyst outperformed commercial Pt catalysts and also offered much higher stability.

Prof Kwon has been working on improving fuel cell catalysts for the past 10 years, motivated by the many ways in which this technology could find its way into our daily lives.

Prof Kwon noted, “DMFCs have a higher energy density than lithium-ion batteries and could therefore become alternative power sources for portable devices, such as laptops and smartphones.”

This development looks very intuitive and clever. The insight from 10 years of effort surely played a role and the results must be very gratifying indeed. The idea of a squirt of methanol powering up a device instead of long charging cycle certainly has a high consumer attraction level and methanol is very common, relatively safe, and cheap.

Lets hope this will economically scale up to commercial manufacturing for consumer applications. Your humble writer would certainly look eagerly at a reliable methanol power source for several devices.


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