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Innovations
New Research Accelerates Development of Organic Solar Cells
Ateam of researchers is working to replace heavy and expensive silicon solar cells currently being used in the solar industry with light and low-cost organic solar cells - made from materials and elements found in plants and animals - which could help in the battle against climate change.
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Most of today’s solar cells are made from silicon and are heavy, rigid, and expensive to produce. By contrast, organic solar cells hold the promise of being lightweight, flexible, and cheap to make. However, organic solar cells have not yet reached the sunlight-toelectricity efficiencies of their silicon-based counterparts, preventing their commercialisation.
Now, researchers from the University of Cambridge, in a global collaboration with experts from Canada, Belgium, New Zealand, and China, have discovered a new fundamental way for energy to move in organic materials at a speed up to 1000’s of times faster than normal, getting steps closer to fully realise the promise of organic photovoltaics. Their findings are reported in the journal Science Advances.
This new movement mechanism, coined “transient exciton delocalization,” allows energy to move and transfer to the surrounding electrical wires incredibly much faster than normal.
“This improvement is made possible by the quantum-mechanical nature of reality, where energy can exist in many places at once, simultaneously”, said first author Alexander Sneyd, a PhD student at Cambridge’s Cavendish Laboratory. “By taking advantage of these quantum-mechanical elements which allow for highly-efficient energy movement, we can make better, more efficient solar cells.”
The research team began by using a highly advanced nanotechnology technique called ‘living crystallization driven self-assembly’ to create nanofibers made from a sulphur and carbon-based polymer. This allowed them to precisely control the position of each of the atoms in the organic nanofiber to create a ‘perfect’ model material. “This was really the secret to the success”, said Dr. Akshay Rao of the Cavendish Laboratory who led the research. “We were able to attain an unprecedented level of structural control, which one could only dream of until very recently.”
The team then shone a laser at the nanofibers to mimic sunlight, and watched the energy move over time using a technique called transient-absorption microscopy to create ‘films’ of the energy transport.
Researchers Make High-activity Photocatalyst Using Gold Nanoclusters
Researchers from Japan have designed a stable, high-performance photocatalyst from gold nanoclusters (NCs) by removing the protective molecules around them.
In a new study published in Angewandte Chemie, Prof. Negishi led a team of researchers, including Assistant Professor Tokuhisa Kawawaki, Mr. Yuki Kataoka, Ms. Momoko Hirata, and Mr. Yuki Akinaga, to dig deep into the mechanism of the ligand removal process in NCs.
Catalysts, which help drive reactions, are ubiquitous, whether as an enzyme in the body that digests food or the catalytic converter in the car that breaks down pollutants. In chemical reactions, catalysts play an important role in making it more efficient. Recently, atomically precise metal NCs that can accelerate various thermal, electrochemical, and photochemical reactions have been used to design useful catalysts. These NCs are tiny particles (less than 2 nanometers) whose properties can be modified by changing their atomic composition. This is why, metal NCs have received considerable attention, with scientists trying to find various ways of synthesizing NCs with unique functions. A popular way of fabricating atomically precise metal NCs is using ligands (molecules or ions that attach themselves to a central metal core). These ligands not only protect the tiny NCs but also affect their chemical reactivity and selectivity. Sometimes, however, the reactivity is lower than expected. To increase the catalytic activity of ligandprotected metal NCs, they are heated in a furnace at high temperatures without oxygen (a process called “calcination”) to remove the ligands from the main cluster. However, heating the particles at very high temperatures can cause the NCs to accumulate, often leading to a decrease in reactivity.
“When the ligands are removed without special treatment, the metal NCs easily aggregate on the support and lose their size-specific properties. It is essential understand the mechanism of ligand calcination to create highly functional heterogeneous catalysts under appropriate conditions,” says Prof. Yuichi Negishi of Tokyo University of Science, Japan, who researches on the synthesis of nanoclusters.
For their experiments, the Japanese researchers synthesized gold NCs protected by two ligands, 2-phenylethanethiolate and mercaptobenzoic acid and then supported them on a photocatalytic metal oxide. Next, the team heated the prepared material at different temperatures ranging from 195°C to 500°C.
Researchers Devise New Methods for 'Solar-to-fuel' Production
In an article published in Coordination Chemistry Reviews, researchers have highlighted the potential of covalent organic frameworks (COFs), a new class of light-absorbing materials, in solar-to-fuel production.
Photocatalysts absorb energy from light to make a chemical reaction happen. The best known photocatalyst is perhaps chlorophyll, the green pigment in plants that helps turn sunlight into carbohydrates. While carbohydrates may be falling out of favor, photocatalysis is garnering more attention than ever. In a photocatalytic process, light falls on a photocatalyst, increases the energy of its electrons and causes them to break their bonds and move freely through the catalyst.
These “excited” electrons then react with the raw materials of a chemical reaction to produce desired products. A top priority in the field of alternate energy research is using photocatalysts to convert solar energy to fuel, a process called “solar-to-fuel production.”
As co-author Dr. Pardeep Singh explains, “Solar energy has been successfully tapped to make electricity, but we are not yet able to efficiently make liquid fuels from it. These solar fuels, like hydrogen, could be an abundant supply of sustainable, storable, and portable energy.”
The specialty of COFs lies in their ability to improve catalysis and add special substituent molecules called “functional groups” to their structure, providing a way around the limitations of existing photocatalysts. This is due to certain favorable properties of COFs such as chemical stability, controllable porosity, and strong electron delocalization, which make them extra stable.
Like the name suggests, COFs consist of organic molecules that are bonded together into a structure that can be tailored to suit various applications. Moreover, strong electron delocalization means that, unlike in semiconductor photocatalysts, the excited electrons recombine midway only infrequently, resulting in more excited electrons for the chemical reaction.
Since these reactions occur at the surface of the photocatalyst, the increased surface area and modifiable porosity of COFs is a huge advantage. COF-photocatalysts find application in the conversion of water to hydrogen, and the production of methane from carbon dioxide, thus promising the dual benefit of producing fuel and mitigating global warming. Furthermore, they can even help with nitrogen fixation, plastics production, and storage of gases.
Researchers Develop Technology to Produce Hydrogen from Agriculture Residue
Researchers from two Pune-based institutes today announced the development of a technique that produces hydrogen directly from agricultural residue. The generated hydrogen can be used in fuel cell-powered vehicles.
Scientists from Sentient Labs, a KPIT Technologies incubated R&D innovation lab, and Agharkar Research Institute (ARI) of Maharashtra Association for the Cultivation of Science (MACS) came together to develop this innovative technology which they claim to be the first of its kind in the world.
This hydrogen generation technology uses agricultural residue rich in cellulose and hemicellulose content – in paddy, wheat, or maize residue. The process uses microbial culture for the direct generation of hydrogen from agricultural residues. It further generates methane, which is utilized for producing additional hydrogen by steam methane reformation. This process can avoid the burning of biomass generated in large measure in the Indian countryside and generate organic manure and CO2, which find applications in various industries.
"Our technology is 25% more efficient as compared to conventional anaerobic digestion processes used today. The innovative two-stage process eliminates the pre-treatment of the biomass, thus making the process economical and environment friendly. This biologically benign process generates digestate rich in nutrients which can be used as organic fertilizer, said Dr. Prashant Dhakephalkar, Director at Agharkar Research Institute.
He further added, "Its by-products can be used as soil conditioners while undigested solids for briquetting can be sold as solid fuel. I thank the scientists and engineers at Agharkar Research Institute &Sentient Labs for this achievement."
Indian scientists have created a redox flow battery based on zinc and iron, which showed strong storage characteristics and no signs of degradation over 30 chargedischarge cycles. Additionally, the battery did not show any signs of dendrite formation, overcoming one of the key challenges for redox-flow batteries based on these low-cost, abundant materials.
The researchers described their invention in the paper "A Dendrite Free Zn-Fe Hybrid Redox Flow Battery for Renewable Energy Storage," published in the journal Energy Storage. The full paper can be accessed here. About two thirds of global greenhouse emissions is caused by burning of fossil fuels for energy purposes and this has spurred great research interest to develop renewable energy technologies based on wind, solar power etc. Redox Flow Batteries (RFB) are receiving wide attention as scalable energystorage systems to address the intermittency issues of renewable energy sources.
However, for widespread commercialization, the redox flow batteries should be economically viable and environmentally friendly. Zinc based batteries are good choice for energy storage devices because zinc is earth abundant and zinc metal has a moderate specific capacity of 820 mA hg−1 and high volumetric capacity of 5851 mA h cm−3. In their paper, the scientists demonstrate a zinc-iron (Zn-Fe) hybrid RFB employing Zn/Zn(II) and Fe(II)/Fe(III) redox couples as positive and negative redox systems, respectively, separated by a selfmade anion exchange membrane (AEM).
The battery, say the scientists, delivers a good discharge voltage of approximately 1.34 V at 25 mA cm−2, with a coulombic efficiency (CE) of 92%, voltage efficiency (VE) of 85% and energy efficiency (EE) of ~78% for 30 charge-discharge cycles. Repeated galvanostatic charge/discharge cycles show no degradation in performance, confirming the excellent stability of the system.
A key advancement in the present Zn-Fe hybrid redox flow battery with AEM separator is that no dendrite growth was observed on zinc electrode on repeated charge-discharge cycles, which was the serious drawback of many previously reported zinc based redox flow batteries.
This study's results show that the operating conditions are crucial impact factors for the cell performance and the Zn-Fe RFB can exhibit good performance at low concentration (1 M) and at low current density (15 mA cm-2). "Thus, we have successfully demonstrated working of a high efficiency and stable Zn-Fe hybrid redox flow battery with no dendrite growth during zinc deposition by optimizing charge-discharge conditions and employing an anion exchange membrane as separator," conclude the scientists.
Solar Cells with Ferroelectric Crystal Lattice Produce 1,000 Times More Power
Researchers from Martin Luther University HalleWittenberg (MLU), Germany, have developed a lattice arrangement of three different layers of ferroelectric crystals that induced a powerful effect in solar cells.
The researchers believe that on integration with the ferroelectric crystal lattice, the solar cells can become thousand times more powerful. They say that combining ultra-thin layers of different materials can raise the PV effect of solar cells by a factor of 1,000. They achieved this by creating crystalline layers of barium titanate (BaTiO3), strontium titanate (SrTiO3), and calcium titanate (CaTiO3) which they alternately placed on top of one another.
Most solar cells are currently silicon-based however, their efficiency is limited. This has inspired researchers to examine new materials, such as ferroelectrics like barium titanate, a mixed oxide made of barium and titanium. However, pure barium titanate does not absorb much sunlight and consequently generates a comparatively low photocurrent.
Ferroelectricity is a characteristic of certain materials that have a spontaneous electric polarization that can be reversed by the application of an external electric field. According to the physicist Dr. Akash Bhatnagar from MLU's Centre for Innovation Competence SiLinano, Ferroelectric means that the material has spatially separated positive and negative charges, the charge separation leads to an asymmetric structure that enables electricity to be generated from light.
Studies of these researchers from MLU were published in the journal Science Advances.
Unlike silicon, ferroelectric crystals do not require a so-called pn-junction to create the PV effect, in other words, no positively and negatively doped layers. This makes it much easier to produce solar panels, explains Dr. Bhatnagar. He explains that the important thing here is that a ferroelectric material alternated with a paraelectric material. Although the latter does not have separated charges, it can become ferroelectric under certain conditions, like low temperatures or when its chemical structure is slightly modified.
